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Gas Tests

Worksheet Overview

QUESTION 1 of 10

Most gases look very similar to each other. If we have some gas (maybe made in an experiment), how can we tell what the gas is?

Gas tests are four short experiments which let us decide whether or not an unknown gas is the gas we think it might be. There are tests for hydrogen, carbon dioxide, oxygen and chlorine. You need to know the experiments and what the results mean- so here they are!

The hydrogen test is called the "squeaky pop" test. 

If we have some gas, and put a flame near it, the hydrogen reacts with oxygen in the air, and we hear a distinctive "squeaky pop". If we don't hear the popping sound, there is no hydrogen present.

In this experiment, acid + metal → salt + hydrogen, and the hydrogen collects in the soap bubbles. If we put a flame near the bubbles, we will hear a squeaky pop. When the flame is in contact with the hydrogen, the reaction which happens is hydrogen + oxygen → water.

The carbon dioxide test is called the limewater test. If we bubble carbon dioxide gas through limewater, the limewater becomes cloudy and white. If this doesn't happen, there is no carbon dioxide present.

"Limewater" is calcium hydroxide dissolved in water. it's a clear, colourless solution. When it reacts with carbon dioxide, we make calcium carbonate. Calcium carbonate is not soluble in water, so we see white clouds. The reaction is calcium hydroxide + carbon dioxide → calcium carbonate + water.

The oxygen test uses a glowing (but not properly lit) splint. If we place this in oxygen, it will relight, so that it burns properly.

The chlorine test uses a piece of damp blue litmus paper. If chlorine is present, the litmus paper will first turn red, then it will bleach white.

And that's it! The best way to use these tests is to predict what you expect to happen, by thinking about the reaction equations before doing an experiment. Then you can decide which tests are worth doing, to check that the gas made is the one you expect, and that the reaction is doing what you think it should.

 

 

What are the things to do to test for hydrogen gas? Tick all the correct answers.

Put a burning flame in the gas.

Put a glowing splint in the gas.

Listen for a "squeaky pop".

Look for clouds.

Check if the splint catches fire.

What are the things to do to test for oxygen gas? Tick all the correct answers.

Put a burning flame in the gas.

Put a glowing splint in the gas.

Listen for a "squeaky pop".

Look for clouds.

Check if the splint catches fire.

What is the test for carbon dioxide? Fill the gaps in this description.

Put a burning flame in the gas.

Put a glowing splint in the gas.

Listen for a "squeaky pop".

Look for clouds.

Check if the splint catches fire.

What substance is produced to make limewater appear milky?

What is the test for oxygen gas?

Oxygen makes a squeaky pop happen.

Oxygen changes the colour of litmus paper.

Oxygen makes a glowing splint relight.

What do we use to test for chlorine gas?

dry blue litmus paper

limewater

damp blue litmus paper

a glowing splint

If we do the damp blue litmus paper test, and chlorine is present, two things happen. Pick the two things which occur, in the right order.

dry blue litmus paper

limewater

damp blue litmus paper

a glowing splint

Match up the gases with their tests.

Column A

Column B

Hydrogen
Turns damp blue litmus paper red, then white
Oxygen
Squeaky pop
Carbon dioxide
Turns limewater milky
Chlorine
Glowing splint relights

If we react zinc with sulfuric acid, which gas test would we expect to give a positive result?

Squeaky pop

Limewater

Glowing splint

Damp blue litmus paper

If we burn methane and collect the gas produced, which gas test would we expect to give a positive result?

Squeaky pop

Limewater

Glowing splint

Damp blue litmus paper

  • Question 1

What are the things to do to test for hydrogen gas? Tick all the correct answers.

CORRECT ANSWER
Put a burning flame in the gas.
Listen for a "squeaky pop".
EDDIE SAYS
For the hydrogen test, we use a burning flame, and listen for a squeaky pop. Everyone calls it a squeaky pop.
  • Question 2

What are the things to do to test for oxygen gas? Tick all the correct answers.

CORRECT ANSWER
Put a glowing splint in the gas.
Check if the splint catches fire.
EDDIE SAYS
Oxygen is very powerful for making combustion happen, so it can make a glowing splint catch fire again.
  • Question 3

What is the test for carbon dioxide? Fill the gaps in this description.

CORRECT ANSWER
EDDIE SAYS
"Limewater" is the name for a calcium hydroxide solution; this turns milky in the presence of carbon dioxide.
  • Question 4

What substance is produced to make limewater appear milky?

CORRECT ANSWER
calcium carbonate
EDDIE SAYS
The reaction is calcium hydroxide + carbon dioxide → calcium carbonate + water. Because calcium carbonate does not dissolve in water, we see milky clouds in the water.
  • Question 5

What is the test for oxygen gas?

CORRECT ANSWER
Oxygen makes a glowing splint relight.
EDDIE SAYS
The oxygen test works because oxygen is so effective at making combustion happen; that's why putting a blanket over a fire (to cut off the oxygen supply) can put a fire out.
  • Question 6

What do we use to test for chlorine gas?

CORRECT ANSWER
damp blue litmus paper
EDDIE SAYS
Litmus paper tests for acids and alkalis; this is relevant for the first part of the chlorine test. Dampening the paper helps the gas react with the solids in the litmus paper.
  • Question 7

If we do the damp blue litmus paper test, and chlorine is present, two things happen. Pick the two things which occur, in the right order.

CORRECT ANSWER
EDDIE SAYS
The chlorine test has two stages. First, the chlorine reacts with hydrogen from the water, making hydrochloric acid- that's why the indicator turns red. Later, bleach is made, which turns the paper white.
  • Question 8

Match up the gases with their tests.

CORRECT ANSWER

Column A

Column B

Hydrogen
Squeaky pop
Oxygen
Glowing splint relights
Carbon dioxide
Turns limewater milky
Chlorine
Turns damp blue litmus paper red,...
EDDIE SAYS
This question is a summary of the really key points from this activity. If you can remember this, you can probably add the details when you need them. Look back at the introduction if you need to.
  • Question 9

If we react zinc with sulfuric acid, which gas test would we expect to give a positive result?

CORRECT ANSWER
Squeaky pop
EDDIE SAYS
Acid + metal should produce hydrogen, so we should try the hydrogen test, which is the squeaky pop test.
  • Question 10

If we burn methane and collect the gas produced, which gas test would we expect to give a positive result?

CORRECT ANSWER
Limewater
EDDIE SAYS
Burning methane should produce carbon dioxide + water, so we should try the carbon dioxide test, which is the limewater test. We can use the same test to check the gas that we breathe out after respiration.
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