Topic: C4.2 lesson 1 Testing for Gases
Spec link: OCR (Kerboodle) C4.2.1 / C3.1.6
Collins C4.7 / C3.5
Time: 70 min
Recorded Assessment: : Self evaluation tasks
Review:
Knowledge about ‘Formula of gases’
Apply To Demonstrate:
1. Hands on practical session to demonstrate
understanding
2. Quiz and Plenary task
Agree Learning Outcomes:
1. Recall tests for the four common
gases (oxygen, hydrogen, carbon
dioxide, chlorine)
2. Identify the four common gases
using the tests
3. Explain why limewater can be
used to test for carbon dioxide
Present New Knowledge:
Powerpoint slides
Videos
Construct Meaning:
Observe demonstrations and discuss to construct
meaning
Bell
Match up the words with their descriptions
Test for Oxygen
Test for Hydrogen
Electrolyte
The substance being broken down
Positive electrode
Makes a ‘popping’ noise when lit
Anode
Splitting a substance using electricity
Cathode
Relights a glowing splint
Anion
Negative electrode
Cation
Positive ion
Electrolysis
Negative ion
Match up the words with their descriptions
Test for Oxygen
Test for Hydrogen
Electrolyte
The substance being broken down
Positive electrode
Makes a ‘popping’ noise when lit
Anode
Splitting a substance using electricity
Cathode
Relights a glowing splint
Anion
Negative electrode
Cation
Positive ion
Electrolysis
Negative ion
LO
Learning objectives:
•Describe the tests to identify the four common
gases (Oxygen, Hydrogen, Carbon dioxide and
Chlorine)
•Identify the four common gases using these
tests
•Explain why limewater can be used for testing
CO2.
LO
Learning Outcomes:
• Distinguish gases using chemical tests.
• Describe how each test works.
• Recognise that carbon dioxide reacts with
lime water to form an insoluble carbonate.
CM
Video link for testing gases
https://www.youtube.com/watch?v=LiAvDpl5aJA
https://www.youtube.com/watch?v=uE_XSjGIDw4
CM
Test for Hydrogen gas
The test for hydrogen uses a burning splint held at the open
end of a test tube of the gas. Hydrogen burns rapidly with a
‘pop’ sound. The basis for this test is that hydrogen is
reacting rapidly as a fuel by burning in oxygen. The product is
water.
Demo or Student Practical:
● Take 20 ml of 1M HCl in a test tube
● Add 2cm strip of Mg ribbon to the test tube with the HCl
● Invert an empty tube to collect the Hydrogen gas liberated during the reaction
by the downward displacement of air
● Use a bung to prevent escape of gas
Test for Oxygen gas
CM
The test for oxygen uses a glowing splint inserted into a test tube of the gas. The
glowing splint relights in oxygen.
Demo: Wear Eye Protection
● In the 250ml Buchner Flask add 0.1g manganese (IV) oxide powder or 1g of
granules
● Fill a 250ml measuring cylinder with water to collect the gas, this allows you
to flush out the apparatus before collecting gas in boiling tubes.
● Ensure the delivery tube goes from the flask to under the Beehive. The
beehive should be covered in water.
● Add about 20 ml of 20 vol Hydrogen Peroxide to the buchner flask
● Invert a boiling tube filled with water above the beehive shelf whilst still under
water to collect the gas.
● Hydrogen peroxide breaks down to release Oxygen gas which is collected by
the downward displacement of water
CM
Test for Chlorine gas
The test for chlorine uses litmus paper. When damp litmus paper is put into
chlorine gas the litmus paper is bleached and turns white. Chlorine can also be
bubbled into water and tested with litmus paper, which bleaches.
Demo:
● Take a test tube half filled with freshly prepared Chlorine
water solution
● Dip indicator paper and see it getting bleached.
CM
Test for Carbon dioxide gas
The test for carbon dioxide uses an aqueous solution of
calcium hydroxide (which is often called ‘limewater’). When
carbon dioxide is shaken with or bubbled through limewater
the limewater turns milky (it looks cloudy).
What is happening with this test?
Limewater is calcium hydroxide. When carbon dioxide is
passed through limewater, the product formed is calcium
carbonate. This white chalky substance (calcium carbonate)
gives a milky appearance to the solution.
Calcium hydroxide + Carbon dioxide → Calcium carbonate +
Water
ATD
Test for Carbon dioxide - Student Practical
1. Take about 20ml 1M HCl solution in one boiling
tube/conical flask
2. Add about 20ml of limewater to another boiling tube
3. Add a spatula full of Calcium Carbonate or 2 to 3 medium
sized marble chips to the HCl solution and seal the end
with the bung on the delivery tube.
4. Insert the other open end of the delivery tube into the
boiling tube containing limewater solution
5. Observe the limewater go from colourless to cloudy/milky
Plenary: Match the images with the names of the
listed gases
1
3
2
4
●
●
●
●
Chlorine
Oxygen
Hydrogen
Carbon dioxide
ATD
Revision Link and Task list
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/chemicalre
actions/preparinggasesrev1.shtml
Tasks:
1. Use the revision link above to explain the three ‘Methods of collecting gases’.
(use pages 1 and 2 of the link)
2. Copy the table and complete the blank cells given on page 3 of the link
3. Write detailed notes for testing Oxygen, Hydrogen, Carbon dioxide and
Chlorine. (page 4 of the link)
4. Take the bitesize test
5. Extension: Collins quiz at the end of topic 4.7
Answers to Collins Quiz
1. Definitely oxygen;
2. Definitely chlorine;
3. Possibly carbon dioxide; other gases will also put out a lighted splint;
4. Definitely carbon dioxide;
5. Possibly hydrogen; other gases (e.g. methane) react explosively with oxygen,
but only hydrogen burns with a squeaky pop