Question
The elements shown are gases at room temperature and pressure.
hydrogen
nitrogen
oxygen
chlorine
(a) State which one of these gases is green.
(b) The gases shown exist as diatomic molecules.
State the name of another element which has diatomic molecules and is a gas at room
temperature and pressure.
(c) When separate samples of each of these gases are placed in a container they will diffuse.
(i) Describe why these gases diffuse.
(ii) State which of these four gases has the highest rate of diffusion.
Explain your answer.
gas ……………………………………………………………………………………………………………………..
explanation ………………………………………………………………………………………………………….
(d) Nitrogen, oxygen and other substances are found in clean, dry air.
(i) State the percentage of nitrogen in clean, dry air.
(ii) Other than nitrogen and oxygen, identify another element found in clean, dry air.
(iii) Identify a compound found in clean, dry air.
(iv) Nitrogen and oxygen can be separated from liquid air.
State the name of this process.
Answer/Explanation
Answer:
(a) chlorine
(b) fluorine
(c) (i) random motion of molecules/particles
(ii) hydrogen
lowest (relative) molecular mass
(d) (i) 78
(ii) argon/Ar
(iv) fractional (1)
distillation (1)
Question
Air is a mixture of gases.
(a) State the percentage of clean dry air which is oxygen. Give your answer to the nearest whole number.
$\%[1]$
(b) Oxygen and nitrogen are useful gases that can be obtained from air.
(i) Name the process used to separate oxygen and nitrogen from liquid air.[5]
(ii) State the property of oxygen and nitrogen that allows these gases to be separated using this process.[1]
(c) Carbon dioxide, $\mathrm{CO}_2$, is a covalent molecule. Complete the diagram to show the electron arrangement in one molecule of $\mathrm{CO}_2$.
Show only the outer electrons.
(d) The graph shows the concentration of carbon dioxide in the atmosphere over a 60‐year period, measured in parts per million (ppm).
The data shown in the graph is of global concern.
Explain why…………………………………………………………………………………………………………………………….. [3]
(e) Name the process in the carbon cycle by which plants remove carbon dioxide from the
atmosphere…………………………………………………………………………………………………………………………….. [1] [Total: 10]
▶️Answer/Explanation
Ans:
4(a) 21
4(b)(i) fractional (1)
distillation (1)
4(b)(ii) (different) boiling point 1
4(c) 2 double bonds (1)
whole molecule correct (2 pairs of lone pairs on each O) (1)
4(d) increase in (concentrations of) carbon dioxide
(carbon dioxide is) greenhouse gas/greenhouse effect
contributes to climate change/global warming
4(e) photosynthesis
Question
This question is about gases.
(a) The following substances are gases at room temperature.
Identify, by letter:
(i) a gas which combines with water to form acid rain [1]
(ii) two gases which exist as diatomic molecules [2]
(iii) a gas which bleaches damp litmus paper [1]
(iv) a gas which is used as an inert atmosphere in lamps [1]
(v) two gases which are found in clean dry air [2]
(vi) two gases which are found in refinery gas. [2]
(b) NF3 has covalent bonds.
(i) What is a covalent bond?[2]
(ii) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of NF3. Show outer shell electrons only.[3]
(c) Air is a mixture. Nitrogen and oxygen are the two most common gases in air.
(i) What is meant by the term mixture?[1]
(ii) State the percentage of oxygen, to the nearest whole number, in clean dry air. [1]
(iii) Describe the steps in the industrial process which enables nitrogen and oxygen to be separated from clean dry air.
Use scientific terms in your answer. [3]
(iv) Which physical property of nitrogen and oxygen allows them to be separated?[1] [Total: 20]
Answer/Explanation
Ans:
1(a)(i) A
1(a)(ii) M1 C
M2 D
1(a)(iii) D
1(a)(iv) B
1(a)(v) M1 F
M2 B
1(a)(vi) M1 G
M2 H
1(b)(i) a shared pair of electrons (between two atoms)
M1 shared electrons
M2 pair of / two electrons
1(b)(ii) M1 three correct bonding pairs from one N atom to each of three F atoms
M2 (3 pairs of) non-bonding electrons on each of three F atoms to complete an octet
M3 (1 pair of) non-bonding electrons on N atom to complete an octet
1(c)(i) two (or more) substances not chemically combined
1(c)(ii) 21(%)
1(c)(iii) fractional distillation of liquid air
M1 air is made into a liquid
M2 (allow air to) boil or evaporate
M3 condense the vapours / collect the vapours in order (of evaporation)
fractional distillation gets M2 and M3
1(c)(iv) boiling points