Edexcel IGCSE Chemistry gases in the atmosphere
Practise atmosphere questions by recalling gas percentages, calculating oxygen volume and explaining combustion or carbon dioxide evidence.
- Syllabus
- First assessment 2019
- Course
- Chemistry 4CH1
Practise atmosphere questions by recalling gas percentages, calculating oxygen volume and explaining combustion or carbon dioxide evidence.
This question is about gases.
The table gives information about five gases.

Use information from the table to answer these questions.
Each gas may be used once, more than once or not at all.
Give the name of the gas that is about 79% of the atmosphere by volume.
nitrogen
ALLOW NX2
Give the name of the gas that is not normally found in the atmosphere.
hydrogen
ALLOW H2
Give the name of the gas that affects global warming.
carbon dioxide
ALLOW COX2
A student uses the reaction between iron and oxygen to find the percentage of oxygen in air.
The diagram shows the apparatus the student uses.

State why the iron powder needs to be wet.
water is needed for iron to rust / react
ALLOW reaction needs water (and oxygen)
ALLOW increases rate of reaction
State the colour of the compound formed in the reaction between iron and oxygen.
brown (coating on iron)
ALLOW red-brown /
orange-brown / orange /
orange-red
IGNORE red alone
Explain the advantage of using iron powder rather than pieces of iron.
An explanation that links the following two points M1 (the powder has) a larger surface area
M2 so the iron will rust quicker/ the reaction will be faster / the results are (obtained) more quickly
IGNORE references to the
collision theory
The syringe in the diagram shows the reading at the end of the experiment.
Complete table 1 to show the readings on the syringe.
Give both values to the nearest 1 cm3.

table 1
| Reading | Volume / cm3 |
|---|---|
| syringe reading at start | 81 |
| syringe reading at end | 16 |
| change in volume | 65 |
Allow:
- error carried forward on the syringe reading at start if the syringe reading at end is read incorrectly
Marking guidance:
- Correct volumes the wrong way round scores 1.
The student repeats the experiment and obtains a different set of results.
Table 2 shows these results.
Use the results from table 2 to calculate the percentage by volume of oxygen in the air.
percentage by volume of oxygen in air = ................................ %

Table 2
- volume of oxygen = 90 - 22 = 68 cm3
- total volume at start = 260 + 90 = 350 cm3
- percentage by volume of oxygen = 68 x 100 / 350 = 19.4%
Allow:
- error carried forward from the first two steps as long as the answer is less than 100%
- any number of significant figures except 1
Marking guidance:
- Correct answer without working scores 3.
- 26.2% scores 2.
- 25.7% scores 2.
- 75.6% scores 2.
- 34.6% scores 1.
This is a question about metals and their compounds.
Magnesium is a metal that burns in air.
State one observation made during the combustion of magnesium metal.
(bright) white flame
ALLOW white light
ACCEPT white solid/ash/powder
(formed)