AQA GCSE Combined Science (8464), Higher tier · Chemistry › Chemical analysis › Identification of common gases
Practise Test for hydrogen. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How to show that a gas is hydrogen: a burning splint held at the mouth of the tube gives a squeaky pop. Usually a 2-mark 'describe a test and give the result' question, sometimes linked to reactions that make hydrogen.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Describe the test for hydrogenHold a burning splint at the open end of a test tube of the gas.
3
State the positive result for hydrogenHydrogen burns rapidly with a pop sound (a 'squeaky pop').
4
Tell the hydrogen and oxygen tests apartHydrogen: burning splint gives a pop. Oxygen: glowing splint relights.
5
Name reactions that produce hydrogenMetals with acids, very reactive metals with water, and electrolysis of many solutions (at the negative electrode).
6
Explain the pop with an equationHydrogen reacts rapidly with oxygen in the air: 2H2 + O2 → 2H2O.
Notes
The test
Collect the gas in a test tube.
Hold a burning splint at the open end (mouth) of the test tube.
If the gas is hydrogen, it burns rapidly with a pop sound (a 'squeaky pop').
Hydrogen is much less dense than air and escapes quickly, so keep the tube stoppered until you test it.
The pop happens because hydrogen reacts rapidly with oxygen from the air to form water: 2H2 + O2 → 2H2O. grade 6+
Where hydrogen comes from
Metals such as magnesium and zinc react with dilute acids to form a salt and hydrogen, e.g. magnesium + hydrochloric acid → magnesium chloride + hydrogen.
Very reactive metals, such as sodium and lithium, react with water to form a metal hydroxide and hydrogen.
In the electrolysis of many solutions, such as sodium chloride solution, hydrogen forms at the negative electrode (cathode).
A burning splint going out does not identify a gas: many gases put out a flame.
Cheatsheet
Test: burning splint held at the open end of a test tube of the gas
Result: hydrogen burns rapidly with a (squeaky) pop
2H2 + O2 → 2H2O (the reaction that makes the pop) grade 6+
metal + acid → salt + hydrogen
reactive metal + water → metal hydroxide + hydrogen
Burning splint = hydrogen test; glowing splint = oxygen test
How to answer each type of question
Describe the test for hydrogen and give the result
2 marks3
Test (1 mark): a burning splint held at the open end of the tube.
Result (1 mark): a (squeaky) pop.
Example. A student adds zinc to dilute sulfuric acid. Bubbles of gas are produced. Describe a test to show that the gas is hydrogen. Give the result of the test.
Show the model answer
Hold a burning splint at the open end of a test tube of the gas (1). The gas burns with a (squeaky) pop (1).
Identify the gas and complete an equation
1 to 3 marks5
Look at the reactants: a metal with an acid, or a reactive metal with water, gives hydrogen.
Use the test result given: a pop with a burning splint means hydrogen.
For metal + water, the other product is the metal hydroxide; for metal + acid, it is a salt.
Example. A small piece of lithium is added to water. It fizzes. A burning splint held at the mouth of a tube of the gas gives a squeaky pop. (a) Name the gas. (b) Complete the word equation: lithium + water → .................... + ....................
Say that hydrogen reacts (burns) rapidly with oxygen in the air.
This rapid reaction makes the pop sound.
Write the balanced equation: 2H2 + O2 → 2H2O.
Example. Explain why hydrogen makes a pop sound when it is tested with a burning splint. Include a balanced equation for the reaction.
Show the model answer
Hydrogen reacts rapidly with oxygen in the air, which makes the pop (1). 2H2 + O2 → 2H2O: correct formulae (1); correctly balanced (1).
Shortcuts and memory tricks
Hydrogen is the gas that burns, so it gets the burning splint. Oxygen helps things burn, so it brings a glowing splint back to life.
'H for Hydrogen, P for Pop': hydrogen pops.
'MASH': Metal + Acid → Salt + Hydrogen.
Where marks are lost
Using a glowing splint: that is the test for oxygen.
Putting the splint into the liquid. Hold it at the open end of a test tube of the gas.
Writing 'it makes a noise' or 'it explodes'. Write 'pop' or 'squeaky pop'.
Giving 'the splint goes out' as the result for hydrogen.
Writing H instead of H2 for hydrogen gas in an equation.
Exam technique
Two marks = test + result: 'burning splint' and 'pop'.
Learn the four gas tests as a set, because questions often ask you to choose between them.
If a question asks how you know a gas is hydrogen, give the test result, not just the reaction that made it.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Name the product of the reaction between hydrogen and oxygen.
water
The squeaky pop happens because hydrogen reacts very quickly with oxygen in the air. Name the product of this reaction.
water
A student adds excess magnesium ribbon to dilute sulfuric acid in a conical flask fitted with a delivery tube, and collects the gas produced over water in an upturned test tube. Name the salt produced in this reaction.
magnesium sulfate
Complete the word equation for the reaction. zinc + hydrochloric acid → .................... + hydrogen
zinc chloride
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy3 marks
A student added magnesium ribbon to dilute hydrochloric acid in a test tube. A gas was produced.
(a) Give one observation that would show a gas is being produced.[1]
(b) The gas was hydrogen. Describe the test for hydrogen and give the result.[2]
Show the answer and mark scheme
(a)
bubbles / fizzing / effervescence
(b)
(hold a) burning / lit splint at the open end of the test tube
(the hydrogen burns rapidly with a) (squeaky) pop
Question 2Medium4 marks
Hydrogen can react rapidly with oxygen from the air. The reaction makes a squeaky pop.
(a) Name the product of the reaction between hydrogen and oxygen.[1]
(b) Balance the equation for the reaction. ....H2 + ....O2 → ....H2O[1]
(c) A student collected a test tube of an unknown gas and put a glowing splint into it. The splint did not relight. The student concluded that the gas was hydrogen. Explain why the student's conclusion is not valid.[2]
Show the answer and mark scheme
(a)Answer: water
water / water vapour / steam
(b)Answer: 2H2 + O2 → 2H2O
2H2 + O2 → 2H2O
(c)
a glowing splint is the test for oxygen / only shows that the gas is not oxygen
to show the gas is hydrogen, hold a burning splint at the mouth of the tube and listen for a (squeaky) pop
Question 3Hard7 marks
A student electrolyses dilute sulfuric acid using inert electrodes. Gas bubbles are produced at both electrodes.
(a) Predict the gas produced at the negative electrode (cathode). Explain your prediction.[2]
(b) Describe a test the student could use to confirm this gas, and give the expected result.[2]
(c) The student collects the gas from the positive electrode and tests it with a lit splint. There is no pop. The student concludes that the gas is oxygen. Explain why this result alone does not justify the conclusion, and describe the test that would confirm it.[3]
Show the answer and mark scheme
(a)Answer: hydrogen
hydrogen
hydrogen ions are attracted to the negative electrode, where they gain electrons (are reduced) to form hydrogen gas
(b)
collect a sample of the gas from the electrode and hold a lit splint at the mouth of the tube
a squeaky pop is heard
(c)
no pop only shows that the gas is not hydrogen; it does not identify the gas