SC/BES/MCS/2006/10
December 2006
Original: English
ADVANCED LEARNING
PACKAGES
MICROSCIENCE ENVIRONMENTAL
EXPERIMENTS
WATER QUALITY AND
WATER TREATMENT
Manual for Learners - First Edition
Compiled by Beverly Bell, Bina Akoobhai et al.
Edited by Prof. JD Bradley
© 2006 RADMASTE Centre
µscience
United Nations Educational,
Scientific and Cultural Organization
The UNESCO-Associated Centre
for Microscience Experiments,
RADMASTE Centre
Prepared under UNESCO Contract No. 4500027737
This Booklet of Environmental Microscience
Experiments has been Prepared in Cooperation
with UNESCO, IOCD and IUPAC
UNITED NATIONS EDUCATIONAL,
SCIENTIFIC AND CULTURAL
ORGANIZATION
INTERNATIONAL ORGANIZATION
FOR CHEMICAL SCIENCES
IN DEVELOPMENT
INTERNATIONAL UNION OF PURE
AND APPLIED CHEMISTRY – IUPAC
IN COLLABORATION WITH
µscience
THE UNESCO-ASSOCIATED CENTRE FOR
MICROSCIENCE EXPERIMENTS
THE RADMASTE CENTRE
UNIVERSITY OF THE WITWATERSRAND
JOHANNESBURG, SOUTH AFRICA
THE INTERNATIONAL FOUNDATION FOR
SCIENCE EDUCATION
JOHANNESBURG, SOUTH AFRICA
SESI
SCIENCE EDUCATION SOLUTIONS
INTERNATIONAL
P.O. BOX 681, WITS 2050,
JOHANNESBURG, SOUTH AFRICA
Worksheets Prepared By :
Ms B. Bell & Ms B. Akoobhai, et al (UNESCO-Associated Centre for
Microscience Experiments, The RADMASTE Centre,
University of the Witwatersrand)
µscience
Worksheets Edited By :
Prof. J. Bradley (International Foundation for Science Education)
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
ADVANCED LEARNING PACKAGES
MICROSCIENCE ENVIRONMENTAL EXPERIMENTS
WATER QUALITY AND WATER TREATMENT
CHAPTER 1 ...........................................................................................
5
SOURCES OF SUBSTANCES IN WATER .................................................... 5
ACTION OF SOAPS AND DETERGENTS ...................................................................................7
EUTROPHICATION .....................................................................................................................8
INDUSTRIAL POLLUTION (SULPHUR DIOXIDE) .......................................................................9
FACTORS INFLUENCING WATER POLLUTION BY AIR POLLUTANTS .................................11
PART 1 WHAT IS THE FUNCTION OF A CHIMNEY IN AN INDUSTRIAL PLANT WHICH EMITS AIR
POLLUTANTS?
PART 2 CAN THE EMISSION OF AIR POLLUTANTS FROM AN INDUSTRIAL PLANT BE ELIMINATED?
SOLUBILITY OF GASES IN WATER ......................................................................................... 13
Part 1: PREPARATION OF SULPHUR DIOXIDE
Part 2: PREPARATION OF CARBON DIOXIDE
Part 3: PREPARATION OF OXYGEN
Part 4: PREPARATION OF NITROGEN
CHAPTER 2 ...........................................................................................16
WATER TESTING ..........................................................................................16
THE TEST FOR DISSOLVED OXYGEN .....................................................................................18
PART 1: HOW CAN WE TEST FOR DISSOLVED OXYGEN IN WATER?
PART 2: WHAT IS THE EFFECT OF TEMPERATURE ON THE CONCENTRATION OF
DISSOLVED OXYGEN IN WATER?
TESTING FOR THE ACIDITY/BASICITY OF DRINKING WATER .............................................21
THE TEST FOR NITRATE IN WATER ....................................................................................... 23
TESTING FOR PHOSPHATE IN DRINKING WATER ................................................................25
PART 1 DOES THE WATER SOURCE THAT YOU DRINK FROM HAVE AN ACCEPTABLE PHOSPHATE
CONTENT? (SILVER NITRATE TEST)
PART 2 DOES THE WATER SOURCE THAT YOU DRINK FROM HAVE AN ACCEPTABLE PHOSPHATE
CONTENT? (AMMONIUM MOLYBDATE TEST)
TESTING FOR THE PRESENCE OF HEAVY METAL IONS IN WATER ...................................27
TESTING THE CONDUCTIVITY OF WATER ............................................................................29
TESTING FOR HARDNESS IN WATER ....................................................................................31
CHAPTER 3 .......................................................................................... 33
WATER TREATMENT................................................................................... 33
THE INDUSTRIAL PURIFICATION OF WATER: CHLORINATION ...........................................35
WATER SOFTENERS: 1 ............................................................................................................37
WATER SOFTENERS: 2 ............................................................................................................38
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
CHAPTER 1
SOURCES OF
SUBSTANCES IN WATER
5
SOURCES OF SUBSTANCES IN WATER
ACTION OF SOAPS AND DETERGENTS ..................................................................... 10
EUTROPHICATION ........................................................................................................ 11
INDUSTRIAL POLLUTION (SULPHUR DIOXIDE) ......................................................... 12
FACTORS INFLUENCING WATER POLLUTION BY AIR POLLUTANTS ...................... 14
PART 1 WHAT IS THE FUNCTION OF A CHIMNEY IN AN INDUSTRIAL PLANT WHICH EMITS AIR
POLLUTANTS?
PART 2 CAN THE EMISSION OF AIR POLLUTANTS FROM AN INDUSTRIAL PLANT BE
ELIMINATED?
SOLUBILITY OF GASES IN WATER .............................................................................. 16
Part 1: PREPARATION OF SULPHUR DIOXIDE
Part 2: PREPARATION OF CARBON DIOXIDE
Part 3: PREPARATION OF OXYGEN
Part 4: PREPARATION OF NITROGEN
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
6
SOURCES OF SUBSTANCES IN WATER
ACTION OF SOAPS AND DETERGENTS
REQUIREMENTS
Apparatus:
Chemicals:
3 x propettes ; 1 x comboplate® ; 2 x toothpicks.
Tap water; cooking oil; dilute dishwashing liquid.
PROCEDURE
1.
Half fill wells F1 and F2 with water using a clean propette.
2.
Using a clean syringe add 5 drops of cooking oil to each of wells F1 and F2. (See Question 1)
3.
With a clean propette add 10 drops of dilute dishwashing liquid to well F1.
4.
Stir the solutions in wells F1 and F2 using clean toothpicks. (See Question 2)
QUESTIONS
Q1.
What do you observe in wells F1 and F2?
Q2.
Describe what you observe in well F1.
Q3.
Explain why there is a difference in observation in wells F1 and F2.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
7
SOURCES OF SUBSTANCES IN WATER
EUTROPHICATION
REQUIREMENTS
Apparatus: 1 x propette ; 2 x vials ; 1 x toothpick; 1 x microspatula, 1 x marking pen.
Chemicals: Pond water (containing algae and plant material); Pentasodiumtriphosphate (Na5P3O10(s)).
PROCEDURE
1.
Add pond water to both the vials using a clean propette, until each is ¾ full. Label one vial as vial 1 and the
other as vial 2.
2.
To vial 1 add 3 microspatulas of pentasodiumtriphosphate. Stir using a toothpick.
3.
Place both the vials in a place with direct sunlight. Leave the vials undisturbed and observe any changes on a
daily basis for 1 week.
QUESTIONS
Q1.
What is the purpose of vial 2?
Q2.
Describe what you observe in vials 1 and 2 after 1, 3, 5, 7 days.
Q3.
Explain why there is a difference in observation in vials 1 and 2.
Q4.
What phenomena is occurring in vial 1? Explain in detail.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
8
SOURCES OF SUBSTANCES IN WATER
INDUSTRIAL POLLUTION (SULPHUR DIOXIDE)
Focus Question: Does an industrial plant emitting sulphur dioxide acidify open water in its vicinity?
REQUIREMENTS
Apparatus: 1 x comboplate®; 1 x lid 2; 1 x 2 ml syringe; 1 x plastic microspatula; 2 x propettes; 1 x plasticine.
Chemicals: Hydrochloric acid (HCl(aq)) [5.5 M]; Anhydrous sodium sulphite powder (Na2SO3(s)); Tap water;
Universal indicator solution.
Introduction
Air pollution has become a big problem in recent years. This experiment aims to simulate an industrial plant, which
produces gaseous sulphur dioxide, and determine what factors influence the effect of the air-pollution on the water
in the vicinity. The small wells of the comboplate®, filled with water, will be used to represent the water supply.
PROCEDURE
1.
Place the comboplate under a running water tap and fill all the small wells (wells A1 to D12) with water.
2.
Use an empty propette to suck up, and then discard any water that may have got into the large wells. Use a
paper towel to gently soak up any water between the small wells on the surface of the comboplate®.
3.
Use a propette to add one drop of universal indicator solution into each of the small wells filled with water.
®
silicone tube
connector
vent
LID 2
4.
Using the spooned end of a plastic microspatula, add three spatulas of anhydrous sodium sulphite powder
into well E3. Insert lid 2 (see figure above) into well E3 in such a way that the vent is closest to the small wells
and the tube connector is pointed away from the small wells.
5.
Seal the tube connector on lid 2 with a piece of plasticine (see the figure below).
pollution source (SO2(g)
emitted from well E3)
water source (all small
wells filled with water
+ universal indicator)
lid 2 with vent hole
facing the small wells
plasticine ball to seal
tube connector on lid 2
If there are any draughts in the room, the results of the experiment may be affected slightly. If you
like, you can use a shallow container such as an empty cardboard box to prevent the effect of any
draughts on the experiment. This is, however, not a necessity.
6.
Fill the syringe with 0,2 ml of 5.5 M hydrochloric acid. Hold the nozzle of the syringe just inside the vent in
lid 2. Add all of the hydrochloric acid into well E3. Do not push the nozzle of the syringe all the way into
the vent of lid 2, because the syringe will become stuck in the lid. Be careful not to drop any of the
hydrochloric acid into the water.
7.
Wait about three to five minutes. While waiting, answer the following questions.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
9
INDUSTRIAL POLLUTION (SULPHUR DIOXIDE)
QUESTIONS
Q 1. What is the colour and pH of the aqueous solution of universal indicator at the beginning of the experiment ?
Q 2. What happens to the colour of the aqueous solution of universal indicator in the wells ? What is happening to
the pH of this solution ?
Q 3. Explain your answer to question 2 using a chemical equation to represent the reaction that could be
occurring.
Q 4. After about 1½ minutes of waiting, briefly lift the comboplate® to the light and observe the colour of the
aqueous solutions from underneath the comboplate®.
Does the colour of the aqueous solution change uniformly:
a) across the surface area of the solution in each well,
b) from top to bottom in each well ?
Q 5. Suggest a reason for your answer to question 4.
Q 6. Is the acidification of the solution the same throughout all the small wells of the comboplate® ? Explain your
answer.
Q 7. In how many wells has the water been acidified ? (Answer this no longer than 5 minutes from the time you
began the experiment.)
Q 8. Would the number of wells showing water acidification be more or less if six microspatulas of sodium sulphite
were added to well E3 instead of three, when the experiment began ? Explain your answer.
Q 9. After counting the number of acidified wells, hold the comboplate to the light once again.
How has the distribution of the acidification changed from the first time you viewed the wells from beneath the
comboplate® ? Explain your answer.
Q10. What is the answer to the focus question?
Clean the comboplate® thoroughly.
EXTENSION QUESTIONS
Q11. Use your answer to question 6 to explain why industrial areas are often located far away from residential
areas.
Q12. Adult fish can often survive in acidic water, but their eggs are killed by acidic conditions. Use your answer to
question 9 to predict the effects of acid rain on populations of living organisms, like fish, over a prolonged
period of time.
Q13. During this experiment, the solutions in the small wells were not disturbed in any way. Use your answer to
question 9 to explain why acid rain can have devastating effects on ecosystems located far downstream from
an industry, which is built near a turbulent river.
Q14. If the vent on lid 2 were sealed with plasticine and the tube connector was left open instead, predict whether
the extent of acidification would increase or decrease if the experiment was repeated? Give a reason for your
prediction.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
10
SOURCES OF SUBSTANCES IN WATER
FACTORS INFLUENCING WATER POLLUTION BY AIR POLLUTANTS
PART 1
Focus Question 1: What is the function of a chimney in an industrial plant which emits air pollutants?
Apparatus:
Chemicals:
1.
REQUIREMENTS
1 x 2 ml syringe; 2 x thin stemmed propettes; 1 x plastic microspatula; 1 x comboplate®; 1 x lid 1;
1 x piece of plasticine (5 mm x 5 mm x 5 mm); 1 x silicone tube (1.5 cm x 4 mm).
Hydrochloric acid (HCl(aq)) [5.5 M]; Anhydrous sodium sulphite powder (Na2SO3(s));
Universal indicator solution; Tap water.
PROCEDURE
Place the comboplate® under a running water tap and fill all the small wells (wells A1 to D12) with water.
2.
Use an empty propette to suck up, and then discard any water that may have got into the large wells. Use a
paper towel to gently soak up any water between the small wells on the surface of the comboplate®.
3.
Use a propette to add one drop of universal indicator solution into each of the small wells filled with water.
4.
Using the spooned end of a plastic microspatula, add three spatulas of
anhydrous sodium sulphite powder into well E3. Insert lid 1 (see figure
alongside) into well E3 in such a way that the tube connector is closest to
the small wells and the syringe inlet is pointed away from the small wells.
3.
Fit the silicone tube over the tube connector on lid 1. This will model the
chimney.
silicone tube
connector
syringe
inlet
LID 1
The remainder of the steps may be performed in a draught-free area.
4.
Fill the syringe with 0,2 ml of 5.5 M hydrochloric acid. Fit the syringe into the syringe inlet in lid 1. Add all of
the 5.5 M hydrochloric acid gently into well E3. Do not add the acid too quickly as the increase in
pressure in the well may force acid out through the silicone tube. Be careful not to drop any of the
hydrochloric acid into the water.
5.
Immediately after completing step 4, remove the syringe from lid 1 and seal the syringe inlet with a piece of
plasticine. Be careful not to drop any of the hydrochloric acid into the water.
lid 1 with tube connector
facing the small wells
pollution source (SO2(g)
emitted from well E3)
water source (all small
wells filled with water
+ universal indicator)
6.
silicone tube fitted over tube
connector to model chimney
plasticine ball to seal
syringe inlet on lid 1
Wait about 3 to 5 minutes and observe. (See Questions 1, 2)
Clean the comboplate® thoroughly before proceeding with part 2.
QUESTIONS
Q1. Is the acidification of the solution the same throughout all the small wells of the comboplate? Explain your
answer.
Q2. In how many wells has the water been acidified? (Measure this no longer than 5 minutes from the time you
began the experiment.)
Q3. Is the number of wells showing water acidification greater or smaller when a chimney is present?
Q4. What is the answer to focus question 1?
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
11
SOURCES OF SUBSTANCES IN WATER
FACTORS INFLUENCING WATER POLLUTION BY AIR POLLUTANTS
PART 2
Focus Question 2:
Apparatus:
Chemicals:
Can the emission of air pollutants from an industrial plant be eliminated?
REQUIREMENTS
1 x 2 ml syringe; 3 x thin stemmed propettes; 2 x plastic microspatulas; 1 x comboplate®; 1 x lid 1;
1 x piece of plasticine (5 mm x 5 mm x 5 mm); 1 x silicone tube (1.5 cm x 4 mm);
1 x piece of cotton wool (3 mm x 3 mm).
Hydrochloric acid (HCl(aq)) [5.5 M]; Anhydrous sodium sulphite powder (Na2SO3(s));
Calcium oxide powder (CaO(s)); Universal indicator solution; Tap water.
PROCEDURE
1.
Repeat steps 1 to 3 in part 1.
2.
Using the spooned end of a plastic microspatula, add three spatulas of anhydrous sodium sulphite powder
into well E3. Insert lid 1 into well E3 in such a way that the tube connector is closest to the small wells and
the syringe inlet is pointed away from the small wells.
3.
Insert a small piece of cotton wool into the opening of one end of
the silicone tube. Thereafter fit this end of the tube over the tube
connector on lid 1.
4.
silicone tube
Use the narrow end of a clean, plastic microspatula to add
tube connector
calcium oxide powder into the other end of the silicone tube.
Add sufficient calcium oxide powder to fill the silicone tube up.
Try to pack the calcium oxide quite tightly into the tube so that it
is not forced out of the tube when the hydrochloric acid is added
into the well. This will be the emission absorber.
CaO powder packed
cotton wool
As in part 1, the remaining steps may be performed in a draught-free area.
5.
Fill the syringe with 0,2 ml of hydrochloric acid. Fit the syringe into the syringe inlet in lid 1. Add all of the
5.5 M hydrochloric acid into well E3. Do not add the acid too quickly as the increase in pressure in the
well may force all the calcium oxide out of the silicone tube. Be careful not to drop any of the
hydrochloric acid into the water.
6.
Immediately after completing step 5, remove the syringe from the inlet in lid 1 and seal the inlet with a piece of
plasticine.
cotton wool
pollution source (SO2(g)
emitted from well E3)
plasticine ball to seal syringe
inlet on lid 1
lid 1
water source
7.
chimney filled with CaO emission
absorber
Wait about three to five minutes and observe. (See Question 1)
Clean the comboplate® thoroughly.
QUESTIONS
Q1. In how many wells has the water been acidified ? (Answer this no longer than 5 minutes from the time you
began the experiment.)
Q2. Write down a balanced chemical equation to show the reaction between the SO2(g) and the CaO(s) in the
chimney.
Q3. What is the answer to focus question 2?
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
12
SOURCES OF SUBSTANCES IN WATER
SOLUBILITY OF GASES IN WATER
There are four gases that will be tested for solubility. These are sulphur dioxide, carbon dioxide, oxygen and
nitrogen. Below is a procedure given for preparing each gas. The class can be divided so that each group can
prepare one gas and observe the solubility collectively. For best results prepare the gases and start the solubility test
on Friday with the results to be observed on Monday.
Part 1:
PREPARATION OF SULPHUR DIOXIDE
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x lid 1; 1 x lid 2; 1 x silicone tube (4 cm x 4 mm); 1 x 2 ml syringe;
1 x plastic microspatula; 1 x piece prestik; 1 x dish for water;
1 x small sample vial marked “sulphur dioxide”.
Chemicals: Hydrochloric acid (HCl(aq)) [5.5 M]; Anhydrous Sodium sulphite powder (Na2SO3(s)); Tap water;
Fridge water that has been previously boiled.
®
PROCEDURE
1.
Fill ¾ of the dish with the fridge water. Place it to one side.
2.
Insert the small sample vial into well F4.
3.
Using the spooned end of the microspatula, put 4 spatulas of solid Na2SO3(s) into well F2.
4.
Seal well F2 with lid 2. Seal the sample vial in well F4 with lid 1.
5.
Connect one end of the silicone tube to the tube connector on lid 2. Connect the remaining end of the silicone
tube to the tube connector on lid 1.
6.
Fill the syringe with 1 ml of 5.5 M HCl(aq) and insert the nozzle of the syringe into the inlet on lid 1.
7.
Inject 1-2 drops of 5.5 M HCl(aq) into well F2. After a while block the opening on lid 1 on the sample vial
with a piece of prestik. Now inject the rest of the 5.5 M HCl(aq) slowly. Wait 1-2 mins after all the 5.5 M
HCl(aq) has been added to well F2.
8.
Now remove lid 1 from the sample vial with one hand and block the opening of the sample vial with the
thumb of your other hand. Quickly invert the sample vial in the water of the dish. Place to one side.
inverted sample vial
containing sulphur dioxide
dish
fridge water
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
13
SOLUBILITY OF GASES IN WATER
Part 2:
PREPARATION OF CARBON DIOXIDE
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x lid 1; 1 x lid 2; 1 x silicone tube (4 cm x 4 mm); 1 x 2 ml syringe;
1 x plastic microspatula; 1 x piece prestik; 1 x dish for water;
1 x small sample vial marked “carbon dioxide”.
Chemicals: Hydrochloric acid (HCl(aq)) [5.5 M]; Calcium carbonate powder (CaCO3(s)); Tap water;
Fridge water that has been previously boiled.
®
PROCEDURE
1.
Fill ¾ of the dish with fridge water. Place it to one side.
2.
Insert the small sample vial into well F4.
3.
Using the spooned end of the microspatula, put 4 spatulas of solid CaCO3(s) into well F2.
4.
Seal well F2 with lid 2. Seal the sample vial in well F4 with lid 1.
5.
Connect one end of the silicone tube to the tube connector on lid 2. Connect the remaining end of the silicone
tube to the tube connector on lid 1.
6.
Fill the syringe with 1 ml of 0.1 M HCl(aq) and insert the nozzle of the syringe into the inlet on lid 1.
7.
Inject 1-2 drops of 0.1 M HCl(aq) into well F2. After a while block the opening on lid 1 on the sample vial
with a piece of prestik. Now inject the rest of the 0.1 M HCl(aq) very slowly. Wait 1-2 mins after all the 0.1 M
HCl(aq) has been added to well F2.
8.
Now remove lid 1 from the sample vial with one hand and block the opening of the sample vial with the
thumb of your other hand. Quickly invert the sample vial in the water of the dish. Place to one side.
Part 3:
PREPARATION OF OXYGEN
REQUIREMENTS
Apparatus: 1 x comboplate®; 1 x lid 1; 1 x lid 2; 1 x silicone tube (4 cm x 4 mm); 1 x 2 ml syringe;
1 x plastic microspatula; 1 x piece prestik; 1 x dish for water;
1 x small sample vial marked “oxygen”.
Chemicals: Manganese dioxide powder (MnO2(s)); Fresh hydrogen peroxide solution (H2O2(aq))[10 %];
Tap water; Fridge water that has been previously boiled.
PROCEDURE
1.
Fill ¾ of the dish with fridge water. Place it to one side.
2.
Insert the small sample vial into well F4.
3.
Using the spooned end of the microspatula, put 4 spatulas of solid MnO2(s) into well F2.
4.
Seal well F2 with lid 2. Seal the sample vial in well F4 with lid 1.
5.
Connect one end of the silicone tube to the tube connector on lid 2. Connect the remaining end of the silicone
tube to the tube connector on lid 1.
6.
Fill the syringe with 1 ml of 10% H2O2(aq) and insert the nozzle of the syringe into the inlet on lid 1.
7.
Inject 1-2 drops of 10% H2O2(aq) into well F2. After a while block the opening on lid 1 on the sample vial
with a piece of prestik. Now inject the rest of the 10% H2O2(aq) slowly. Wait 1-2 mins after all the 10%
H2O2(aq) has been added to well F2.
8.
Now remove lid 1 from the sample vial with one hand and block the opening of the sample vial with the
thumb of your other hand. Quickly invert the sample vial in the water of the dish. Place to one side.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
14
SOLUBILITY OF GASES IN WATER
Part 4:
PREPARATION OF NITROGEN
REQUIREMENTS
Apparatus: 1 x dish for water; 1 x small sample vial marked “nitrogen”.
Chemicals: Fridge water that has been previously boiled.
PROCEDURE
1.
Fill ¾ of the dish with fridge water.
2.
Since the air is made up of 78 % nitrogen, the air in the sample vial will be used as a sample of nitrogen gas.
Invert the sample vial in the water of the dish. Place to one side.
QUESTIONS
1.
Why does the water rise in some of the tubes and not in others?
2.
Compare the extent to which the water has risen in each vial.
3.
What does this tell you about the solubility of each of the gases?
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
15
CHAPTER 2
WATER TESTING
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
16
WATER TESTING
THE TEST FOR DISSOLVED OXYGEN ......................................................................... 22
PART 1: HOW CAN WE TEST FOR DISSOLVED OXYGEN IN WATER?
PART 2: WHAT IS THE EFFECT OF TEMPERATURE ON THE CONCENTRATION OF
DISSOLVED OXYGEN IN WATER?
TESTING FOR THE ACIDITY/BASICITY OF DRINKING WATER ................................. 25
THE TEST FOR NITRATE IN WATER ............................................................................ 27
TESTING FOR PHOSPHATE IN DRINKING WATER .................................................... 29
PART 1 DOES THE WATER SOURCE THAT YOU DRINK FROM HAVE AN ACCEPTABLE
PHOSPHATE CONTENT? (SILVER NITRATE TEST)
PART 2 DOES THE WATER SOURCE THAT YOU DRINK FROM HAVE AN ACCEPTABLE
PHOSPHATE CONTENT? (AMMONIUM MOLYBDATE TEST)
TESTING FOR THE PRESENCE OF HEAVY METAL IONS IN WATER ....................... 31
TESTING THE CONDUCTIVITY OF WATER ................................................................. 33
TESTING FOR HARDNESS IN WATER ......................................................................... 35
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
17
WATER TESTING
THE TEST FOR DISSOLVED OXYGEN
Part 1:
How can we test for dissolved oxygen (O2(aq)) in water?
REQUIREMENTS
Apparatus: 1 x comboplate®; 1 x glass sample vial; 1 x stopper to fit glass vial; 1 x 2 ml syringe;
3 x thin stemmed propettes; 1 x plastic microspatula; 1 x thermometer.
Chemicals: Manganese(II) sulphate solution (MnSO4(aq));
Sodium hydroxide-potassium iodide solution (NaOH/KI(aq)); Hydrochloric acid (HCl(aq)) [11M];
Soluble starch powder; Tap water.
INTRODUCTION
Dissolved oxygen in the water is very important for organisms that live in the water, such as fish, frogs, and water
insects. If the level of dissolved oxygen (DO) changes, the water ecosystems can be affected, eg. a decrease in the DO
concentration can cause the death of one or more life stages of certain water insects.
PROCEDURE
Record the location of the test site and the temperature of the water below:
Place where water was collected:
Temperature of water:
1.
Immerse the sample vial into the water, which you are going to test. Allow the vial to fill until it is overflowing. If
you are collecting water from a tap, gently fill the sample vial with the water from the tap until the vial is
overflowing. Make sure that there are no air bubbles trapped in the sample vial. Do not place the stopper into
the vial.
2.
Carefully place the sample vial on a surface upon which you can work without upsetting the water sample.
Insert the 2 ml syringe into the solution of manganese(II) sulphate (MnSO4(aq)) and remove 0,5 ml of the
solution. There must not be any air bubbles in the syringe!
3.
Place the tip of the syringe containing the MnSO4(aq) about halfway into the sample vial. Carefully push in the
plunger of the syringe and add all of the MnSO4(aq) to the water sample.
Some of the sample will flow out of the vial. Do not be concerned about this.
4.
Rinse the syringe with clean tap water and dry it. Insert the cleaned syringe into the sodium hydroxidepotassium iodide solution (NaOH/KI(aq)) and remove 0,5 ml of this solution. Make sure that you do not have
any air bubbles in the syringe.
5.
Insert the syringe about halfway into the sample vial as before and carefully add all of the NaOH/KI(aq) to the
water sample. (See Question 1)
6.
Once you have completed step 5, push the stopper into the sample vial. This must be done in such a way that
some of the water is pushed out of the vial. This will prevent any air bubbles from entering the sample vial.
7.
When the stopper is firmly in place, invert the sample vial (turn it upside down) a few times to mix the
contents of the vial.
8.
Allow the precipitate to settle about halfway down the sample vial and then invert the vial again to remix the
contents. Allow the precipitate to settle as before.
9.
Rinse the 2 ml syringe with clean tap water and dry it. Fill the syringe with 1 ml of 11 M hydrochloric acid
(HCl(aq)), making sure that no air bubbles are present in the syringe.
Be very careful with the hydrochloric acid. If any acid drops onto the skin, rinse
immediately with water.
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18
10.
Carefully remove the stopper from the sample vial so that no air enters the water sample. Insert the tip of
the 2 ml syringe about halfway into the sample vial and add all of the 11 M HCl(aq) to the sample. (See
Question 2)
11.
Replace the stopper in the sample vial in the same way as you did before. Carefully invert the sample vial a
few times to mix the contents of the sample vial. (See Question 3)
12.
Continue to mix the contents of the vial until all of the precipitate is dissolved. There should be no visible solid
particles floating in the sample.
The oxygen in the sample is now "fixed". The sample can be exposed to air at this stage. (If the
sample has not been collected in the classroom, it can now be transported back there.)
13.
Rinse the 2 ml syringe again with tap water and dry it. Insert the syringe into the sample vial and remove
2 ml of the sample from the vial.
14.
Dispense the 2 ml sample from the syringe into well F1 of the comboplate®.
15.
Pick up the plastic microspatula. Insert the narrow end of the microspatula into the soluble starch powder
and remove a little powder. The powder must not be heaped on the microspatula. Tap the microspatula
gently to remove excess powder.
small quantity of starch powder
at end of microspatula
16.
Add the starch powder to the water sample in well F1. Stir the contents of well F1 to mix in the starch
indicator. (See Question 4)
17.
Put the comboplate® to one side. Do not throw away the sample in well F1 because you need it for Part 2.
QUESTIONS
Q1.
What do you notice in the sample vial after adding both the MnSO4(aq) and the NaOH/KI(aq) to the water?
Q2.
What happens inside the sample vial when the HCl(aq) is added?
Q3.
What happens while the contents of the vial are being mixed?
Q4.
What happens in well F1 when the starch indicator is added?
Q5.
What is the answer to the focus question?
Q6.
Do you think more or less oxygen dissolves in warm water than in cold water?
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19
THE TEST FOR DISSOLVED OXYGEN
Part 2:
What is the effect of temperature on the concentration of dissolved oxygen in water?
The temperature of the water can affect how much oxygen from the atmosphere will dissolve in the water. To determine the concentration of oxygen dissolved in the water, one can observe how dark the blue black colour of the starch
indicator becomes when it is added to the water sample. If the concentration of dissolved oxygen is small, the indicator
is more purple in colour and if there is a larger concentration of dissolved oxygen, the starch indicator will be more black
in colour.
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x glass sample vial; 1 x stopper to fit glass vial; 1 x 2 ml syringe;
3 x thin stemmed propettes; 1 x plastic microspatula.
Chemicals: Manganese(II) sulphate solution (MnSO4(aq));
Sodium hydroxide-potassium iodide solution (NaOH/KI(aq)); Hydrochloric acid (HCl(aq)) [11M];
Soluble starch powder; Tap water; Boiled water cooled to 300C - 400C.
®
PROCEDURE
1.
Collect the water sample provided (30 - 40°C) in the same way as instructed in step 1 of Part 1. Repeat steps
2 to 7 in Part 1 using the warm water sample. (See Question 1)
2.
Repeat steps 8 to 12 in Part 1 with the warm water sample.
3.
Once the oxygen has been "fixed", remove the stopper from the sample vial. Clean the 2 ml syringe and
use it to withdraw 2 ml of the sample from the vial.
4.
Transfer the sample from the syringe into well F2 of the comboplate®.
5.
The sample should already be pale yellow in colour. Use the narrow end of a clean microspatula to add the
same quantity of starch indicator powder to the sample in well F2 as you did to well F1 (see step 15 in Part 1).
Stir the contents of well F2 with the microspatula.
QUESTIONS
Q1.
What is the difference between the precipitate formed with the water sample in Part 1 and that formed with
the warm water sample here, after the addition of the MnSO4(aq) and the NaOH/KI(aq)?
Q2.
Compare the colour of the solution you obtained with the warm water in well F2 with that from Part 1 in well
F1, after the starch has settled at the bottom of the well. What is the difference between the two solutions?
Q3.
Examine the colour of the solid indicator at the bottom of each well by looking directly down into wells F1 and
F2. What is the difference between the two solids?
Q4.
Is the concentration of oxygen dissolved in the water sample lower or higher at the higher temperature? Give
a reason for your answer.
Q5.
What is the answer to the focus question?
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RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
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20
WATER TESTING
TESTING FOR THE ACIDITY/BASICITY OF DRINKING WATER
Focus Question:
What is the acidity/basicity of the water source that you drink from?
REQUIREMENTS
Apparatus: 1 x comboplate®; 5 x thin stemmed propettes; 1 x plastic microspatula; 1 x filter funnel;
1 x filter paper.
Chemicals: Sodium hydroxide solution (NaOH(aq)) [0.10 M]; Hydrochloric acid (HCl(aq)) [0.10 M];
Universal indicator solution; Tap water.
PROCEDURE
1.
Dispense 10 drops of HCl (0.10 M) into well A1.
2.
Dispense 10 drops of tap water into well A2.
3.
Dispense 10 drops of NaOH (0.10 M) into well A3.
4.
Add 1 drop of universal indicator solution into each well.
Note the colour of the solution in each well and write this down in Table 2. (See Question 1)
**
Stir the solution in each well with a cleaned plastic microspatula if you are uncertain of the colour
change.
5.
Dispense 10 drops of sample water into well A4. (This sample can be obtained from a river, a pond, or any
other source that you'd like to test. However, make sure to filter off any solid particles (mud, sticks, grass etc.)
that may interfere with this test. Use the filter funnel and filter paper for this purpose.)
6.
Add 1 drop of universal indicator solution into well A4.
Note the colour of this solution and write this down in Table 2. (See Question 2)
**
Stir the solution in well A4 with a cleaned plastic microspatula if you are uncertain of the colour
change.
Rinse the wells with tap water, and then shake them dry.
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RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
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21
TESTING FOR THE ACIDITY/BASICITY OF DRINKING WATER
QUESTIONS
Q1.
Construct a table like Table 2 in your books.
Use Table 1 to describe the acidity/basicity of the solutions in wells A1, A2 and A3 i.e. whether the solutions
are very acidic, slightly acidic, neutral, slightly basic or very basic.
Record your observations in the space provided in Table 2.
TABLE 1
Colour of Universal Indicator Solution in Sample Tested
Description
Dark Red to Light Red
Very acidic
Dark Orange to Yellow
Slightly acidic
Light Green
Neutral
Dark Green to Dark Blue
Slightly basic
Light Purple to Dark Purple
Very basic
TABLE 2
Well Number
Colour of Universal Indicator Solution
Description
A1
A2
A3
A4 (water sample)
Q2.
Use Table 1 to describe the acidity/basicity of the water sample in well A4. Record your observation in Table
2 as before.
The acidity/basicity of each sample tested may be different. Thus the answers obtained for well
A4 may vary.
Q3.
What is the answer to the focus question?
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RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
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22
WATER TESTING
THE TEST FOR NITRATE IN WATER
Focus Question: Does the water source that you test have an acceptable * nitrate (NO3-(aq)) concentration
for drinking?
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 1 x thin stemmed propette; 1 x plastic microspatula; 1 x lid 1;
1 x lid 2; 1 x silicone tube; 1 x filter funnel; 1 x filter paper.
Chemicals: Sodium hydroxide solution (NaOH(aq)) [5.0 M]; Devarda's alloy (5%Zn: 50%Cu: 45%Al);
Magnesium nitrate solution (Mg(NO3)2(aq)) [0.001 M]; Universal indicator solution.
®
syringe
inlet
tube connectors
vent
syringe
LID 1
silicone tube
LID 2
0.2 ml 5.0 M NaOH(aq)
0.5 ml 0.001 M Mg(NO3)2(aq)
tap water
2 spatulas Devarda’s Alloy
PROCEDURE
1.
Fill ¾ of well F1 with water from the tap. Add one drop of universal indicator solution into the water, with a
propette. Note the colour of the universal indicator. (See Question 1)
2.
Using the spooned end of the microspatula, put 2 microspatulas of Devarda's alloy into well F2.
3.
Use the syringe to add 0.5 ml of magnesium nitrate solution into well F2. Thoroughly clean the syringe with
water before proceeding with the next step.
4.
Seal well F1 with lid 2. Make sure the vent hole faces inwards (see figure above). Seal well F2 with lid 1.
5.
Connect one end of the silicone tube to the silicone tube connector on lid 1. Connect the remaining end of the
silicone tube to the silicone tube connector on lid 2.
6.
Refill the cleaned syringe with 0.2 ml of sodium hydroxide solution (5.0 M) and connect the nozzle of the
syringe into the syringe inlet on lid 1 (see the figure above for the complete set-up).
7.
Inject the 0.2 ml of sodium hydroxide solution (5.0 M) very slowly into well F2. Shake the comboplate®
gently back and forth a couple of times to thoroughly mix the contents in well F2.
Make sure the appropriate lids are placed in wells F1 and F2 or the base may be forced
up through the silicone tube, making it necessary to restart the experiment.
8.
Wait about 1 minute, from the time you added the sodium hydroxide, and observe what happens. (See
Questions 2 - 5)
9.
After about 5 minutes, remove the lid from well F1 and smell the contents as before to confirm your previous
observation. Note the colour of the universal indicator solution. (See Question 6)
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23
10.
Clean the comboplate® thoroughly, then repeat steps 1 to 9. This time use a water sample of unknown
composition in step 3. (This sample may be obtained from a river, a pond, or any other water source that
you'd like to test. However, make sure to filter off any solid particles (mud, sticks, grass etc.) that may prevent
you from detecting a pH change. Do this first with the filter funnel and filter paper supplied.)
11.
Answer Question 7.
QUESTIONS
Q1.
Is the water acidic, basic or neutral?
Q2.
What do you observe happening in well F2?
Q3.
Can you smell anything from the vent in well F1?
(Wave your hand across the vent bringing your nose close to the vent, but not directly over it.)
If you can smell something, describe what you smell.
Q4.
What gas do you think this is?
Q5.
Write down a chemical formula for the gas formed in well F2.
Q6.
What is the colour of the indicator?
Is the solution in the well acidic, basic or neutral? What do you deduce from this observation?
Q7.
What is the answer to the focus question?
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RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
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24
WATER TESTING
TESTING FOR PHOSPHATE IN DRINKING WATER
Part 1
Focus Question: Does the water source that you drink from have an acceptable phosphate (PO43- (aq))
content?
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 3 x thin stemmed propettes; 1x plastic microspatula;
1 x filter funnel; 1 x filter paper.
Chemicals: Disodium hydrogenphosphate solution (Na2HPO4(aq)) [0.001 M]; Silver nitrate (AgNO3(aq)) [0.10 M];
Dilute nitric acid (HNO3(aq)) [2.0 M]
®
PROCEDURE
1.
Use a propette to half fill well F1 with the solution of disodium hydrogenphosphate (0.001 M).
2.
Add 10 drops of silver nitrate solution (0.10 M) into well F1. (See Question 1)
3.
Add 10 drops of dilute nitric acid (2.0 M) to well F1. (See Question 2)
4.
Repeat steps 1 to 3 in well F2, with a water sample of your choice. This sample may be obtained from a river,
a pond, or any other water source that you'd like to test, from which you drink. However, make sure to filter off
any solid particles (mud, sticks, grass etc.) that may prevent you from detecting a colour change. Do this first
with the filter funnel and paper supplied. (See Question 3)
Rinse the wells with tap water, and then shake them dry.
QUESTIONS: Part 1
Q1.
Note what happens as the silver nitrate is added to F1.
Q2.
Note what happens as the nitric acid is added to F1.
Q3.
Observe what happens when the test is repeated with your water sample in F2.
If there is no colour change when testing your sample this could mean a number of things:
Q4.
1.
The concentration of phosphates present in the water is lower than this test can detect.
2.
No phosphates are present.
What is the answer to the focus question?
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
25
WATER TESTING
TESTING FOR PHOSPHATE IN DRINKING WATER
Part 2
Focus Question: Does the water source that you drink from have an acceptable phosphate (PO43- (aq))
content?
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 3 x thin stemmed propettes; 1x plastic microspatula;
1 x filter paper; 1 x filter funnel.
Chemicals: Disodium hydrogenphosphate solution (Na2HPO4(aq)) [0.001 M]; Dilute nitric acid (HNO3(aq)) [2.0 M];
Ammonium molybdate reagent ((NH4)2MoO4(aq)).
®
PROCEDURE
1.
Use the 2 ml syringe to dispense 0,5 ml of the disodium hydrogenphosphate solution (0.001 M) into well F1.
2.
Rinse the syringe with tap water. Use the cleaned syringe to add 0,3 ml of the nitric acid to the Na2HPO4(aq)
in well F1.
3.
Rinse the syringe again and use it to add 1,5 ml of the ammonium molybdate reagent to the solution in well
F1. (See Question 1)
4.
Repeat steps 1 to 3 in well F2, with a water sample of your choice. This sample may be obtained from a river,
a pond, or any other water source that you'd like to test, from which you drink. However, make sure to filter off
any solid particles (mud, sticks, grass etc.) that may prevent you from detecting a colour change. Do this first
with the filter funnel and paper supplied. (See Questions 2, 3)
Rinse the wells with tap water, and then shake them dry.
QUESTIONS: Part 2
Q1.
Note what happens as the ammonium molybdate reagent is added to F1.
Q2.
Observe what happens when the test is repeated with your water sample in F2.
If there is no colour change when testing your sample this could mean:
Q3.
1.
The concentration of phosphates present in the water is lower than this test can detect.
2.
No phosphates are present.
What is the answer to the focus question?
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
26
WATER TESTING
TESTING FOR THE PRESENCE OF HEAVY METAL IONS IN WATER
Focus Question: Does the water source that you test have any heavy metal ions (e.g. Cu2+(aq), Zn2+(aq),
Pb2+(aq)) present?
REQUIREMENTS
Apparatus: 1 x comboplate®; 1 x 2 ml syringe; 5 x thin stemmed propette; 3 x plastic microspatula; 1 x lid 1;
1 x lid 2; 1 x silicone tube; 1 x filter funnel; 1 x filter paper.
Chemicals: Hydrochloric acid (HCl(aq)) [5.5 M]; Iron sulphide powder (FeS(s));
Copper nitrate solution (Cu(N03)2(aq)) [0.1 M]; Zinc nitrate solution (Zn(N03)2 (aq)) [0.1 M];
Lead nitrate solution (Pb(N03)2(aq)) [0.1 M]; Tap water; Water sample.
If any acid is spilt on the skin thoroughly rinse the affected area with water.
tube connectors
syringe
inlet
vent
syringe
LID 1
silicone tube
LID 2
0.5 ml 5.5 M HCl (aq)
1 level spatula
of FeS(s)
tap water
F1
F2
PROCEDURE
1.
Fill ¾ of well F1 with water from the tap.
2.
Put 1 level microspatula of solid iron sulphide (FeS(s)) into well F2, using the spooned end of the
microspatula.
3.
Seal well F1 with lid 2. Make sure the vent hole faces inwards (see figure). Seal well F2 with lid 1.
4.
Connect one end of the silicone tube to the silicone tube connector on lid 1. Connect the remaining end of the
silicone tube to the silicone tube connector on lid 2.
5.
Fill the syringe with 0.5 ml of 5.5 M HCl and connect the nozzle of the syringe into the syringe inlet on lid 1
(see figure above for complete set-up).
6.
Inject the 0.5 ml of 5.5 M HCl very slowly into well F2.
Make sure the appropriate lids are placed in wells F1 and F2 or the acid may be forced
up through the silicone tube, making it necessary to restart the experiment.
7.
Wait about 3 minutes, from the time you added the hydrochloric acid. Answer Questions 1 - 3 while you wait.
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27
8.
After 3 minutes has elapsed, use the empty propette provided to suck up most of the aqueous hydrogen
sulphide solution in well F1.
9.
Add 8 drops of aqueous hydrogen sulphide (H2S(aq)) solution into wells A1, A2 and A3.
10.
Add 5 drops of the copper nitrate solution (0.1 M) into well A1. Stir the solution with a clean microspatula. (See
Question 4)
11.
Add 5 drops of lead nitrate solution (0.1 M) into well A2. Stir the solution with a different microspatula. (See
Question 5)
12.
Add 5 drops of zinc nitrate solution (0.1 M) into well A3. Stir the solution with a different microspatula. (See
Question 6)
13.
Add 8 drops of sample water of unknown composition in wells B1, B2, B3. This sample may be obtained from
a river, a pond, or any other water source that you'd like to test. However, make sure to filter off any solid
particles (mud, sticks, grass etc.) that may prevent you from detecting a colour change. Use the filter funnel
and filter paper provided to do this.
14.
Add 5 drops of the remaining aqueous hydrogen sulphide solution into each well. (See Question 7)
QUESTIONS
Q1.
What do you observe happening in well F1?
Q2.
Can you smell anything from the vent in well F1? If so, what do you think this smell is due to?
Q3.
Write down a chemical formula for the gas formed in well F2.
Gaseous hydrogen sulphide is a weak acid. When it dissolves in water the following reaction
H2S(g) + H2O(l)
HS-(aq) + H3O+(aq)
occurs:
Thus well F1 contains an aqueous solution of hydrogen sulphide.
Q4.
Note the appearance of the mixture in well A1. Explain what you observe.
Q5.
Note the appearance of the mixture in well A2. Explain what you observe.
Q6.
Note the appearance of the mixture in well A3. Explain what you observe.
We see from these observations that aqueous hydrogen sulphide reacts with heavy metal ions in solution
to form insoluble metal sulphides.
Q7.
What is the answer to the focus question?
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RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
28
WATER TESTING
TESTING THE CONDUCTIVITY OF WATER
Focus Question: What can testing the conductivity of a water sample, tell us about that sample?
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 1 x thin stemmed propette; 1x plastic microspatula;
1 x LED current indicator with connections; 1 x filter funnel; 1 x filter paper; 1 x 9V battery.
(or Bar LED Conductivity Meter)
Chemicals: Hydrochloric acid (HCl(aq)) [0.1 M]; Tap water; Water sample.
®
INTRODUCTION
In this experiment hydrochloric acid will be diluted in a series dilution. The aim of this experiment is to determine
what effect diluting this solution will have on the conductivity, and then to compare this conductivity with a sample of
water of unknown composition.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
PROCEDURE
Use the syringe to add 0.1 ml of hydrochloric acid (0.10 M) into well E1.
Rinse the syringe with tap water to clean it. Add 1.9 ml of tap water into well E1.
Stir the solution in well E1 with the spooned end of the microspatula to mix the contents.
Make sure that the syringe is dry inside, then suck up 0.1 ml of the solution in well E1 with the syringe. Place
this into well E2. Rinse the syringe with tap water to clean it. Dispense 1.9 ml of tap water into well E2.
Stir the solution in well E2 with the spooned end of the cleaned microspatula to mix the contents.
Make sure that the syringe is dry inside, then suck up 0.1 ml of the solution in well E2 with the syringe. Place
this into well E3. Rinse the syringe with tap water to clean it. Dispense 1.9 ml of tap water into well E3.
Stir the solution in well E3 with the spooned end of the cleaned microspatula to mix the contents.
Make sure that the syringe is dry inside, then suck up 0.1 ml of the solution in well E3 with the syringe. Place
this into well E4. Rinse the syringe with tap water to clean it. Dispense 1.9 ml of tap water into well E4.
Stir the solution in well E4 with the spooned end of the cleaned microspatula to mix the contents.
Push the lid with the current indicator into well E6.
Connect the current indicator to the terminals of the 9 V battery, as shown in the diagram.
Connect each of the crocodile clips to a carbon rod (pencil lead) as shown in the diagram.
Insert the carbon rod connected to the long black wire into the solution in well E1. Insert the carbon rod
connected to the long end of the red wire into the same solution in well E1. Take care that the carbon rods do
not touch in the solution.
crocodile clips connecting
wires of the LED to the
carbon rods
carbon rods
immersed in the
HCl(aq) in well E1
black wire connected to positive
terminal of the battery
red wire connected to
negative terminal of
the battery
light emitting
diode (LED) in E6
_
+
9V
BATTERY
E1
E6
14. Observe what happens to the red light emitting diode (LED) in the current indicator. (See Questions 1, 2)
15. Wipe the carbon rods clean and then test the conductivity of the solutions in wells E2, E3 and E4 in the same
way. (See Question 3)
16. Use the clean syringe to add 2.0 ml of sample water into well E5. This water sample may be obtained from a
river, a pond, or any other water source that you'd like to test. However, make sure to filter off any solid
particles (mud, sticks, grass etc.) that may interfere with this test. Test the conductivity of the sample as before.
(See Questions 4, 5)
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RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
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29
TESTING THE CONDUCTIVITY OF WATER
QUESTIONS
Q1.
Prepare a table like Table 1 below.
Table 1. Experimental observations
Well
Concentration
HCl(aq)/M
E1
0.10
E2
0.010
E3
0.0010
E4
0.00010
LED glow: very dull, dull, bright, very
bright?
E5 (sample water)
Q2.
Enter your observations from step 14.
Q3.
Enter your observations from step 15.
Q4.
Record your results for your water sample in the table. (Note: Your answers may vary according to the
water source that you tested.)
Q5.
What is the answer to the focus question?
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
30
WATER TESTING
TESTING FOR HARDNESS IN WATER
Focus Question:
How can soap be used to test for hardness in water?
INTRODUCTION
As water flows over rocks and soil, it dissolves a large number of chemicals present in the soil and making up the
composition of the rock (eg. limestone, chalk etc.) If water contains large concentrations of dissolved calcium and/or
magnesium ions (Ca2+(aq) and Mg2+(aq)), it is commonly called "hard water". Other ions, such as iron(III) ions, can
also contribute to the hardness of water. In natural waters, however, the concentrations of the Ca2+(aq) and Mg2+(aq)
ions exceed that of any other metal ion. As a result, when we refer to the hardness of water, we mean the total
concentration of calcium and magnesium dissolved in the water. This is expressed as mg/l of calcium carbonate
(CaCO3).
The main household problem associated with hard water is that it interferes with the cleaning action of soaps and
detergents. When soap is mixed with normal, "soft" water (i.e. water containing low concentrations of Ca2+(aq) and
Mg2+(aq)), it dissolves and forms a solution with a foam, or sudsy layer, on top. In contrast, a mixture of soap and
hard water forms very little or no foam. The hard water cleans poorly, depositing a scum on clothes, skin and hair.
If the water contains very high concentrations of calcium and magnesium ions, solid deposits of scale form inside
water pipes. These deposits can become so thick that nearly all of the water flow through the pipe is cut off. Such
deposits inside hot water heaters produce rock-like scales that act as thermal insulators. The heat flowing from the
flame in a gas heater or from a heating element in an electric heater, is partially blocked. The heater can waste up to
25% of its energy because it requires more time to produce hot water.
Extreme water hardness can also affect the metabolism of certain organisms. In our homes, we use a solution
called a softener to remove the calcium and magnesium ions in the water used for washing clothes. Water supplied
by wells is often very hard, and the calcium and magnesium ions are removed from the water with an ion exchange
resin. The resin consists of polymer beads with sodium ions (Na+) attached to them. When hard water flows through
the resin, the calcium ions become attracted to the polymer beads while the sodium ions leave the resin and mix
with the water. The ions are exchanged because the polymer beads have a greater attraction for the calcium ions
than for the sodium ions.
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 6 x thin stemmed propettes.
Chemicals: Soap Solution [0.025%];
Calcium chloride solution (CaCl2(aq)) [0.1 M], [0.01 M], [0.001 M], [1 x 10-4 M]; * 'Soft' tap water.
®
PROCEDURE
1.
2.
3.
4.
5.
6.
7.
Using the 2 ml syringe, dispense 0,5 ml of the 0.025% soap solution into each of wells F1, F2, F3, F4 and
F5.
Rinse the syringe thoroughly with clean tap water. Use the clean syringe to add 0,5 ml of "soft" water to the
soap solution in well F1.
Rinse the syringe again with tap water. Use the clean syringe to add 0,5 ml of the 1 x 10-4 M calcium
chloride solution to the soap solution in well F5. Similarly, add 0,5 ml of the 0.001 M calcium chloride
solution to the soap solution in well F4. Add 0,5 ml of the 0.01 M calcium chloride to the soap solution in well
F3. Add 0,5 ml of the 0.1 M CaCl2(aq) to the soap solution in well F2.
If the calcium chloride solutions are added as set out in step 3, from least concentrated to most
concentrated, then the syringe does not need to be rinsed between solutions.
Use a propette to suck up all of the solution (1 ml) in well F1.
Using 4 more clean propettes, repeat step 4 with the solutions in wells F2 to F5.
Shake each propette for about 30 seconds. Note what happens to the solution inside each propette while
you are shaking it.
Stand the propettes in the comboplate for about 15 minutes by placing the bulb of each propette into one of
the empty, large wells of the comboplate®.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
31
TESTING FOR HARDNESS IN WATER
QUESTIONS
Q 1. What do you notice after 15 minutes about the foam in the propette which contains the "soft" water and soap?
Q 2. What has happened to the foam in the propettes which contained the 0.1 M and the 0.01 M CaCl2(aq)
solutions after 15 minutes?
Q 3. Have the foams of the 0.001 M and 1 x 10-4 M CaCl2(aq) solutions changed in appearance after 15 minutes?
Explain the changes, if any, in each foam.
Q 4. Use your answers to questions 1 to 3 to explain how hard water affects the ability of soap to form a foam.
Q 5. What is the answer to the focus question?
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
32
CHAPTER 3
WATER TREATMENT
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
33
WATER TREATMENT
THE INDUSTRIAL PURIFICATION OF WATER: CHLORINATION ................................ 41
WATER SOFTENERS: 1 ................................................................................................ 43
WATER SOFTENERS: 2 ................................................................................................ 44
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
34
WATER TREATMENT
THE INDUSTRIAL PURIFICATION OF WATER: CHLORINATION
Focus Question:
How can we chlorinate water?
INTRODUCTION
Before water can be used for human consumption, it must be purified at a water treatment plant. A combination of
several procedures are used in the purification process. Some of these procedures include:
Screening: A metal screen is used to prevent fish, sticks, weeds and other large objects from entering the treatment
plant.
Sand filtration: The screened water is passed through a number of sand filters to remove any suspended wastes.
Chlorination: Chlorine has been used for decades to purify water. It has powerful disinfecting properties and kills
bacteria, cysts, algae and viruses which are pathogenic (disease-causing). It also reacts with dissolved organic
substances, such as phenols, to help decompose these. Sometimes, industrial wastes are chlorinated to destroy
cyanides, to oxidise iron, or to reduce undesirable qualities in effluents such as colour and odour. Chlorine is added
to the water at two steps in the water purification process. The pre-chlorination step involves adding chlorine to the
sand filtered water. The post-chlorination step involves adjusting the chlorine concentration in the water just before it
leaves the treatment plant, so that there is a small excess (residual) of chlorine in the water to destroy any bacteria
that may enter the water supply after it leaves the plant.
Chlorine may be added to water in three different ways. If a large quantity of water must be purified, chlorine gas
(Cl2(g)) is used. It is stored in tanks at high pressure as a liquid. As the liquid is released from the tank, the
pressure is reduced and it changes to chlorine gas, which is bubbled into the water at controlled concentrations. At
smaller water treatment plants, a cheaper alternative is to introduce an aqueous solution of sodium hypochlorite
(NaOCl(aq)) into the water. Dilute sodium hypochlorite solutions are available as laundry bleaches. The simplest
method of chlorinating water is to add a solid substance, calcium- or sodium hypochlorite (Ca(OCl)2(s) or
NaOCl(s)), to the water. It is available as pellets or a powder, and is commonly used to chlorinate swimming pool
water.
The purification of water is due to the hypochlorous acid molecule, HOCl. When either chlorine gas, aqueous
sodium hypochlorite or solid calcium hypochlorite is dissolved in water, the hypochlorous acid molecule is formed.
This molecule is responsible for killing the pathogenic organisms in the water.
REQUIREMENTS
Apparatus: 1 x comboplate ; 1 x 2 ml syringe; 1x plastic microspatula; 1 x lid 1; 1 x lid 2; 1 x silicone tube;
2 x pieces blue litmus paper; 1 x felt-tip pen.
Chemicals: Hydrochloric acid (HCl(aq)) [5.5 M]; Potassium permanganate powder (KMnO4(s)); Tap water.
®
tube connectors
syringe inlet
syringe
vent
LID 1
LID 2
silicone tube
1.0 ml 2.75 M HCl(aq)
1 microspatula KMnO4(s)
tap water
F1
F2
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
35
THE INDUSTRIAL PURIFICATION OF WATER: CHLORINATION
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
PROCEDURE
Using the spooned end of the microspatula, place 1 level spatula of solid potassium permanganate into well
F1.
Place lid 1 on well F1.
Dilute the 5.5 M hydrochloric acid to 2.75 M hydrochloric acid by filling the syringe with 0.5 ml of tap water
and dispensing it into well F6. Refill the syringe with 0.5 ml of 5.5 M HCl(aq) and add this dropwise to the
water in well F6. You now have 2.75 M HCl(aq). Use this acid in step 4.
Fill the syringe with 1.0 ml of the 2.75 M HCl(aq) from well F6 and fit the syringe into the inlet in lid 1 covering well F1.
Fill ¾ of well F2 with tap water. Test the effect of the water on a piece of indicator paper. (See Question 1)
Cover well F2 with lid 2.
Join well F1 to well F2 by means of the silicone tubing.
Inject the solution of hydrochloric acid [2.75 M] dropwise into well F1 from the syringe. (See Questions 2-4)
After about 7 – 8 minutes, remove the lid from well F2. Using another piece of indicator paper, test the
effect of the solution in well F2 on the paper. (See Question 5)
Write your initials on a strip of white paper using a koki pen. Place the paper into the solution in well F2.
(See Question 6)
AS SOON AS YOU HAVE COMPLETED THE TEST FOR THE EFFECT OF THE SOLUTION ON THE INK, RINSE THE COMBOPLATE®
THOROUGHLY OR THE BROWN SOLUTION WILL STAIN THE WELLS. IF THIS HAPPENS, ADD A FEW DROPS OF 10% H2O2(aq) TO
THE STAINED WELLS AND SCRAPE THE WELLS CLEAN WITH A TOOTHPICK OR MATCHSTICK.
QUESTIONS
Q 1.
Q 2.
Q 3.
Q 4.
Q 5.
Q 6.
Q 7.
Q 8.
Q 9.
Q10.
Q11.
Q12.
Q13.
Record the colour of the indicator paper with tap water.
What happened in well F1 when you added hydrochloric acid to the potassium permanganate?
What do you observe in the water in well F2 after HCl(aq) is added to the KMnO4(s)?
Can you smell anything coming from the vent in the lid of well F2? (If you are unsure, wave your hand across
the vent towards your nose.) Identify the smell.
What is the colour of this second piece of indicator paper?
What happens to the ink on the white paper?
Explain the observations you made with the indicator paper and the ink writing on the white paper.
Name the gas formed in well F1 and write its chemical formula.
Write a chemical equation for the reaction occurring between the gas formed in well F1 and the water in well
F2.
What type of reaction occurred in well F1? (Hint: Think about the oxidation states of the different species in
the reactants and the products.)
Justify your answer to question 10.
From your answers to questions 10 and 11, what kind of substances are required to obtain chlorine from
hydrochloric acid?
Examine the chemical equation you have written for question 9, as well as the following equation showing the
reaction of aqueous sodium hypochlorite (bleach) with water. Identify and name the species in these
equations that are responsible for the purification of water.
NaOCl(aq) + H2O(l) → NaOH(aq) + HOCl(aq)
Q14. What is the answer to the focus question?
EXTENSION QUESTIONS
Q15. Which of the following substances would you use to produce chlorine (Cl2(g)) from hydrochloric acid
(HCl(aq))? Explain your choice.
1. Sodium chloride (NaCl(s))
2. Manganese dioxide (MnO2(s))
3. Potassium chloride (KCl(s))
Q16. Write down a balanced chemical equation to show the reaction involved when solid calcium hypochlorite
(Ca(OCl)2(s)) is added to swimming pool water. Use the equation to explain why it is used in pool water.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
36
WATER TREATMENT
WATER SOFTENERS: 1
REQUIREMENTS
Apparatus: 1 x propette; 1 x comboplate®; 1 x plastic retort stand ; 1 x plastic arm; 1 x microspatula;
2 x 2 ml syringes.
Chemicals: Calcium chloride solution (CaCl2.2H2O(aq)) [0.01 M];
Ammonium oxalate solution (COONH4)2.H2O(aq)) [1.0 M];
Amberlite (cross-linked polystyrene-divinyl benzene matrix) resin; Tap water.
1.
2.
3.
4.
5.
6.
7.
8.
PROCEDURE
Push the plastic retort stand into well D12 of the comboplate. Push the plastic arm onto the retort stand and
orient the arms on the central stem of the retort stand so that one arm is directly above well F6.
Remove the plunger from the syringe. Using a microspatula add Amberlite to the syringe until it is threequarters full. Place the syringe in the arm that is directly above well F6.
Using a clean propette, add tap water to the syringe. If the syringe is not three-quarters full, add more
Amberlite. Continue adding water until the water coming out at the bottom of the syringe into well F6, is clear.
Remove the plastic retort stand (with the syringe) from well D12 and push it into well D1. Orient the arm so
that the arm with the syringe is directly above well F1. (See diagram below.)
Using a clean syringe, dispense 2 ml calcium chloride solution [0.01 M] into well F2.
Add 1 drop of ammonium oxalate solution to well F2. (See Question 1)
Using the syringe, slowly dispense 1,5 ml of calcium chloride solution [0.01 M] into the syringe containing
the Amberlite.
Add 1 drop of ammonium oxalate solution to well F1. (See Question 2)
retort stand
syringe
plastic arm
QUESTIONS
Q 1. What do you observe in well F2 ?
Q 2. Describe what you observe in well F1.
Q 3. Explain the difference in observation in wells F1 and F2.
Q 4. Write a chemical equation for any chemical reactions you propose.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
37
WATER TREATMENT
WATER SOFTENERS: 2
REQUIREMENTS
Apparatus: 2 x propettes; 1 x comboplate®; 1 x glass rod; 1 x microspatula.
Chemicals: Calcium chloride solution (CaCl2.2H2O(aq)) [0.01 M];
Ammonium oxalate solution (COONH4)2.H2O(aq)) [1.0 M];
Pentasodiumtriphosphate (Na P O (s)).
5
3
10
PROCEDURE
1.
Using a clean propette, dispense calcium chloride solution [0.01 M] into well F1 and F2 until each is half full.
2.
Add 1 drop of ammonium oxalate solution to both wells F1 and F2. (See Question 1)
3.
To well F2, add half a microspatula of pentasodiumtriphosphate. Use the glass rod to stir the solution in well
F2. (See Question 2)
4.
Add a further half a microspatula of pentasodiumtriphosphate to well F2. Stir the solution again. (See
Question 3)
5.
Continue with step 4 until the solution in well F2 is clear. (See Question 4)
pentasodiumtriphosphate
calcium chloride solution + one
drop ammonium oxalate solution
QUESTIONS
Q 1. What do you observe in both wells F1 and F2 ?
Q 2. Describe what you observe in well F2.
Q 3. Describe any further change in well F2.
Q 4. Explain what you observe and write a chemical equation for any chemical reactions you propose.
The UNESCO-Associated Centre for Microscience Experiments
RADMASTE Centre, University of the Witwatersrand, Johannesburg, South Africa
Tel: (+) 27 11 717 4802 Fax: (+) 27 11 403 8733 email: [email protected] website: www.microsci.org.za
38
The UNESCO-associated Centre
for Microscience Experiments
RADMASTE Centre
University of the Witwatersrand
19th Floor, University Corner
Corner Jorissen and Bertha Street
Braamfontein, Johannesburg
South Africa
Private Bag 3
WITS 2050
Tel: (+) 27 11 717 4802
Fax: (+) 27 11 403 8733
email: [email protected]
website: www.microsci.org.za