Self-directed Learning:
Experimental Chemistry
Task
€ Read additional notes and Chapter 1 and 2 of textbook.
€ Complete Review Questions (answers will be made available in school portal on 22
Feb for self check)
€ Complete Worksheet and submit on 1 March 2010, Monday
€ A quiz will be conducted on this topic in week 9 (1 to 5 March 2010)
Overview
Chemistry is typically an experimental science and relies primarily on practical work. It is
important for students to lean the techniques of handling laboratory apparatus and to pay
special attention to safety while working in the laboratory.
In this section, students examine the appropriate use of simple apparatus and chemicals,
and the experimental techniques. Students need to be aware of the importance of purity in
the electronic, pharmaceutical, food and beverage industries. Students should be able to
appreciate the need for precision and accuracy in making readings and also value the need
for safe handing and disposing of chemicals.
Learning Outcomes
Additional notes and Chapter 1: Measurements in Chemistry
After completing this chapter, students should be able to:
• Name appropriate apparatus for the measurement of time, temperature, mass and
volume, including burettes, pipettes measuring cylinders and gas syringes
• Suggest suitable apparatus, given relevant information, for a variety of simple
experiments, including collection of gases and measurement of rates of reaction.
• State that concentrated sulfuric acid is used as a drying agent.
Chapter 2: Purification of Substances
After completing this chapter, students should be able to:
• Describe methods of separation and purification for the components of the following
types of mixtures:
(i) solid-solid
(ii) solid-liquid
(iii) liquid-liquid (miscible and immiscible)
Techniques to be covered for separations and purification include:
(i)
use of a suitable solvent, filtration and crystallisation or evaporation
(ii)
sublimation
(iii)
distillation and fractional distillation
(iv)
use of a separating funnel
(v)
paper chromatography
•
•
•
•
Describe paper chromatography and interpret chromatograms including comparison
with ‘known’ samples and use of Rf values
Explain the need to use locating agents in the chromatography of colourless
compounds
Deduce from the given melting point and boiling point the identities of substances
and their purity.
Explain that the measurement of purity in substances used in everyday life, e.g.
foodstuffs and drugs is important.
Sec3 Pure Chem/Experimental Chemistry/WLK/10
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Review Questions:
1. Complete the table.
Measurement of
Apparatus
Accuracy
SI Unit
a) Time
b) Temperature
c) Mass
°C
Weighing balance
Depends on
apparatus
d) An approximate volume of liquid
e) An accurate volume of liquid
f) A very accurate volume of liquid
g) Volume of gas
Note: 1dm3 = ___________ cm3
1 tonne = ___________ kg
2. What is the volume of the liquid in the measuring cylinder? _______________
50
SPA skill
Always place the measuring cylinder on the table and read off at eye
level to prevent parallax error
40
Think Time (answers will not be provided)
Why the apparatus in the figure on the right
cannot be a measuring cylinder?
3. Name one suitable piece of laboratory apparatus for
(a) Measuring the volume of about 80 cm3 of a liquid
__________________________
(b) Adding exactly 18.5 cm3 of liquid to a beaker
__________________________
(c) Collecting and measuring 80 cm3 of gas
__________________________
(d) Adding exactly 25.0 cm3 of a solution to a flask
__________________________
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4. What is a pure substance?
5. Is white sugar a pure substance? How do you know if a substance is pure?
6. What are some of the industries that need pure substances to make products?
7. Describe how you would obtain pure copper(II) sulfate crystals from an impure sample of
copper(II) sulfate. (State the method used and the procedure)
8. Can common salt be obtained from salt water by crystallization?
9. Name 3 substances that sublime.
10. The diagram shows the experimental setup for separating a
mixture of petrol and water. Which liquid is water?
Stopper
_______________________
Separating
funnel
11. What are miscible liquids?
____________________________________________
Liquid A
Liquid B
Tap
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12. Refer to the diagram below when answering the following questions.
Think Time
(answers will not
be provided)
How is
fractional
distillation
(a) similar to,
and
(b) different
from simple
distillation?
•
Purpose of antibumping granules
(boiling stones)
•
Direction of water
flow in the
condenser
•
Position of
thermometer
(a) Why should the bulb of the thermometer be placed near / opposite the opening of the
side arm?
(b) Why the cooling water should enter the condenser jacket through the lower tube and
leave by the upper tube?
13. Air is a mixture. The main gases in air are shown in the table. Which gas will distill first?
Which part of the fractionating column will it come out from? Label it on the diagram.
Gas
Water vapour
Carbon dioxide
Xenon
Krypton
Oxygen
Argon
Nitrogen
Boiling Point/°°C
100
-78 (sublimes)
-108
-153
-183
-186
-196
Note: Sometimes, the various fractions
collected may have to be redistilled to
effect a more complete separation.
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Applications of fractional distillation:
a. Crude oil - separated into different fractions having different boiling point ranges.
Different fractions have different uses.
b. Liquid air - Air is cooled until it is liquefied and then fractionated into nitrogen and oxygen.
c. Fermented liquor - The dilute ethanol solution obtained after fermentation is concentrated
and purified by fractional distillation.
Investigate:
How does a fractionating column work?
How can we increase the efficiency of separation?
How does paper chromatography separate the substances in a mixture?
14. The following is a chromatogram of sugars in a fruit juice
(a) How many different sugars does the fruit juice contain?
(b) What are the sugars present in the fruit juice?
______________
___________________________
(c) Sugars are colourless substances, how to make them visible on chromatogram?
_____________________________________________________________________
(d) How can you tell from the chromatogram that sucrose is a pure sugar?
___________________________________________________________________
Things to Note for chromatography:
• The starting line must be drawn in pencil and not in ink to prevent ink line from dissolving
in the solvent and interfere with the results.
•
The starting line must be above the solvent level at the start of the experiment to prevent
it from dissolving in the solvent.
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15. Identify the unknown sugar in the following chromatogram by calculating its Rf value and
compare it with the given Rf values of sugars in the table.
Sugar
fructose
glucose
maltose
Sucrose
galactose
Rf values
0.86
0.57
0.40
0.20
0.69
The unknown sugar is ____________________
16. State the technique used to carry out each of the following processes. Choose from the
options below.
Filtration
Distillation
Use of a separating funnel
Fractional distillation
Crystallisation
Paper chromatography
a) To obtain drinking water from muddy water
b) To separate chalk from a mixture of chalk and
copper(II) sulfate solution
c) To separate petrol from crude oil
d) To separate olive oil from water
e) To remove leaves from a swimming pool
f)
To obtain pure sugar from a solution
g) To determine whether the colouring in a fruit
juice is a single substance or a mixture of
coloured substances
17. Circle the correct word.
If a liquid is impure, it boils at a (higher / lower) temperature than the pure liquid.
Impurities will also (increase / lower) the melting point of solids.
18. An impure sample of substance X melts at about 113oC. The table below gives a list of
substances with a melting point near 113oC. Which of the substance(s) could be X?
Substance
Resorcinol
Catechol
Nitrophenol
Butanamide
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Melting point of pure
substance (oC)
111
105
114
115
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19. The article below is extracted from
http://www.dailymail.co.uk/news/article-1235538/AA-warning-There-salt-roads-cleardays-Britain-heads-snow.html
Snow to hit the UK tomorrow as experts warn the country only has
enough salt to keep roads clear for six days
Snow showers are due to hit parts of the UK tomorrow, with much heavier showers expected
in areas during the rest of the week, forecasters said today.
Gritters around the country have been put on high alert for the cold snap which could see
temperatures plummet to -4C.
The Met Office believes the midlands and eastern areas are likely to be hardest hit by the
arrival of snow showers over the next few days.
Weathermen have also said it is too early to
know what will happen on Christmas Day.
Shortage?: Salt for gritting the roads is
piled up at the Salt Union mine in
Winsford Cheshire last Thursday
Scotland saw lows of -5°C last night, while
the North West dropped to -4°C and East
Anglia and the South East saw temperatures
down to -2°C.
‘It’s looking cold over the next few days,’ said Forecaster Gemma Plumb from MeteoGroup
UK.
But motoring group AA warned that half of local authorities only have enough salt
ice roads for six days.
to de-
As Tuesday and Wednesday were predicted to see some of the coldest weather this winter,
the motoring organisation said town halls had a quarter of a million tonnes less road salt in
that they would have carried a decade ago.
The AA president Edmund King said he had sought assurances from the Local Government
Association there would not be a repeat of the February 2009 snow chaos on the roads.
How does salt de-ice roads?
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20. Name the common drying agent for the following gases.
Gas
Drying agent
Gas
Drying agent
Hydrogen
Ammonia
Oxygen
Carbon dioxide
21. The following is a diagram showing the apparatus and chemicals for preparing, drying
and collecting carbon dioxide. Correct the mistakes in the diagram.
Zinc carbonate
Concentrated sulfuric acid
22. Ammonium chloride reacts with aqueous sodium hydroxide to produce ammonia gas.
Draw the apparatus for the preparation of pure, dry ammonia.
23. A gas is insoluble in water and less dense than air. An impure supply of X contains water
vapour and a water-soluble impurity.
In which order should the pieces of apparatus be joined together to collect a pure, dry
sample of X?
A 1, 2, 3, 4
B 1, 2, 3, 5
C 1, 3, 2, 5
D 1, 3, 2, 4
(
)
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