Q: A student heats 100 cm³ of air with copper filings and finds the final volume is 79 cm³. What percentage of oxygen was present in the original air sample?

$$\frac{21}{100} \times 100 = 21\%$$

Question 1

Which gas makes up the largest proportion of dry air by volume?

Accepted Answer

Nitrogen

Question 2

In the copper experiment for determining the percentage of oxygen in air, what is the balanced chemical equation for the reaction between copper and oxygen?

Accepted Answer

$$2Cu(s) + O_2(g) \rightarrow 2CuO(s)$$

Question 3

A student heats 100 cm³ of air with copper filings and finds the final volume is 79 cm³. What percentage of oxygen was present in the original air sample?

Accepted Answer

$$\frac{21}{100} 	imes 100 = 21\%$$

Question 4

Which of the following is a reason why the iron rusting experiment might give a value less than 21% for oxygen in air?

Accepted Answer

The experiment was not left for long enough for all the oxygen to react.

Question 5

What is the main observation when magnesium burns in oxygen?

Accepted Answer

An intense white flame and a white powder is produced.

Question 6

Which oxide is formed when sulfur combusts in oxygen, and what is its reaction with water?

Accepted Answer

Sulfur dioxide ($$SO_2$$), which reacts with water to form sulfurous acid ($$H_2SO_3)$$

Question 7

Which of the following best describes why carbon dioxide is a greenhouse gas but nitrogen is not?

Accepted Answer

CO$$_2$$ can absorb IR radiation because its polarity changes during vibration, while N$$_2$$ remains non-polar.

Question 8

Which process is used to produce carbon dioxide in the laboratory by heating a solid compound?

Accepted Answer

Thermal decomposition of copper(II) carbonate

Question 9

What is the balanced equation for the thermal decomposition of copper(II) carbonate?

Accepted Answer

$$CuCO_3(s) \rightarrow CuO(s) + CO_2(g)$$

Question 10

Which of the following is a real-world consequence of increased atmospheric CO$$_2$$ due to the greenhouse effect?

Accepted Answer

Melting of polar ice caps

Question 11

Which of the following best explains why water vapor is a greenhouse gas?

Accepted Answer

Its polarity changes as it vibrates, allowing it to absorb IR radiation.

Question 12

Which of the following is a property of metal oxides?

Accepted Answer

They are usually basic and react with acids to form salts.

Question 13

A student wants to test for the presence of carbon dioxide gas. Which method should they use?

Accepted Answer

Bubble the gas through limewater and observe if it turns milky.

Question 14

Which equation represents the combustion of hydrogen in oxygen?

Accepted Answer

$$2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$$

Question 15

Which of the following is a correct statement about the greenhouse effect?

Accepted Answer

It is caused by greenhouse gases absorbing and re-emitting IR radiation.

Question 16

Which of the following is a reason why noble gases are present in only trace amounts in the atmosphere?

Accepted Answer

They are chemically unreactive and do not form compounds easily.

Question 17

Which of the following best describes the difference between metal and non-metal oxides?

Accepted Answer

Metal oxides are usually basic and non-metal oxides are usually acidic.

Question 18

Which reaction is used industrially to produce quicklime (calcium oxide)?

Accepted Answer

$$CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$$

Question 19

Which of the following is a correct observation when sulfur burns in oxygen?

Accepted Answer

A blue flame and a colorless, poisonous gas are produced.

Question 20

Why is it important to use excess phosphorus in the experiment to determine the percentage of oxygen in air?

Accepted Answer

To ensure all the oxygen reacts and none is left unreacted.

Gases in the Atmosphere and Their Chemical Properties

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