Group 0, Group 1 & Group 7 – GCSE Chemistry exam questions with mark scheme

1Grade 6–75 marks

Lithium, sodium and potassium are in Group 1 of the periodic table.

(a) Potassium reacts with water to produce potassium hydroxide and hydrogen.

Write a balanced symbol equation for this reaction. [2]

(b) Explain why potassium is more reactive than sodium. [3]

(a) $\text{K} + \text{H}_2\text{O} \rightarrow \text{KOH} + \text{H}_2$ (all formulae correct)(1)
(a) balanced: $2\text{K} + 2\text{H}_2\text{O} \rightarrow 2\text{KOH} + \text{H}_2$ allow multiples; ignore state symbols(1)
(b) potassium’s outer electron is further from the nucleus / potassium has more (electron) shells answers must be comparative; ignore ‘potassium has more electrons’(1)
(b) so there is less (electrostatic) attraction between the nucleus and the outer electron allow more shielding(1)
(b) so the outer electron is lost more easily(1)
Answer: (a) 2K + 2H₂O → 2KOH + H₂ (b) outer electron further from nucleus, weaker attraction, lost more easily
Examiner tip: Group 1 metals lose an electron — saying the atom “gains” electrons or that potassium has “more electrons to lose” will cost you the final mark in (b), and every point must be comparative (further, weaker, more easily).

2Grade 6–75 marks

A student added chlorine water to potassium bromide solution.

(a) Give the colour of the solution at the end of the reaction. [1]

(b) Complete the word equation for the reaction. [1]

chlorine + potassium bromide → ________ + ________

Explain why. Refer to electrons in your answer. [3]

(a) orange allow yellow / orange-brown / brown(1)
(b) potassium chloride + bromine (both needed)(1)
(c) iodine is less reactive than chlorine (so cannot displace it) allow chlorine is more reactive than iodine(1)
(c) iodine’s outer shell is further from the nucleus (than chlorine’s) / iodine has more shells allow iodine atoms are larger / more shielding; answer must be comparative(1)
(c) so it is harder for iodine to gain an electron allow less attraction for an incoming electron; allow converse statements about chlorine throughout (c), e.g. chlorine's outer shell is closer to the nucleus so it gains an electron more easily(1)
Answer: (a) orange (b) potassium chloride + bromine (c) iodine less reactive; outer shell further from nucleus so gains an electron less easily
Examiner tip: Halogens gain electrons — the trend is the reverse of Group 1, so reactivity decreases down the group.

3Grade 4–54 marks

The table shows the boiling points of some Group 0 elements.

Element	Boiling point in °C
neon	−246
argon	−186
krypton	−153
xenon	?

(a) Predict the boiling point of xenon. [1]

(b) Explain why the Group 0 elements are unreactive. [2]

(a) any value between −140 °C and −90 °C (actual −108 °C)(1)
(b) they have a full / stable outer shell (of electrons) allow stable arrangement of electrons / 8 electrons in the outer shell (2 for helium); ignore 'full shells' without reference to outer shell or electrons(1)
(b) so they do not easily gain, lose or share electrons allow do not need to gain or lose electrons(1)
(c) argon is unreactive / inert so the hot filament does not react with it allow oxygen in air would react with / burn / oxidise the filament(1)
Answer: (a) about −110 °C (any value from −140 to −90 °C) (b) full outer shell, so do not readily lose/gain/share electrons (c) argon is unreactive so the hot filament does not burn / oxidise
Examiner tip: Your prediction must continue the trend (increasing) — check it is higher than krypton’s boiling point.

4Grade 1–3Foundation4 marks

The diagram shows the electronic structures of three atoms, X, Y and Z.

(a) Which atom, X, Y or Z, is an atom of a Group 0 element? [1]

(b) Which atom, X, Y or Z, is an atom of an alkali metal? [1]

Give the formula of a chlorine molecule. [1]

(d) Atom X is an atom of sodium. Sodium reacts with chlorine.

Name the compound formed. [1]

(a) Z allow argon(1)
(b) X allow sodium(1)
(c) $\text{Cl}_2$ do not accept Cl², CL2 or Cl(1)
(d) sodium chloride do not accept sodium chlorine; ignore formula NaCl if given with the name; NaCl alone scores(1)
Answer: (a) Z (b) X (c) Cl₂ (d) sodium chloride
Examiner tip: Halogens are diatomic: writing Cl or Cl² instead of Cl₂ loses the formula mark.

5Grade 4–5Foundation5 marks

A teacher adds a small piece of sodium to a trough of water. The water contains a few drops of universal indicator.

(a) Give two observations the students would see as the sodium reacts. [2]

(b) Name the gas produced. [1]

Give the final colour of the universal indicator and explain why it changes colour. [2]

(a) any one from: fizzing / bubbles / effervescence; floats; moves (quickly) around the surface; melts into a ball; gets smaller / disappears ignore 'gas is produced'; ignore explodes(1)
(a) a second different observation from the list above allow universal indicator turns purple / blue if not credited in (c)(1)
(b) hydrogen allow H₂; do not accept H(1)
(c) purple allow blue / violet(1)
(c) (because) sodium hydroxide is formed, which is alkaline allow an alkali / hydroxide ions (OH⁻) form; allow the solution has a pH above 7(1)
Answer: (a) e.g. fizzes, floats and moves around, melts into a ball, disappears (b) hydrogen (c) purple; sodium hydroxide (an alkali) forms
Examiner tip: 'A gas is given off' is a conclusion, not an observation: write what you would see, such as fizzing.

6Grade 6–75 marks

Sodium is cut with a knife. The freshly cut surface is shiny but soon becomes dull.

(a) Explain why the cut surface becomes dull. [1]

(b) Sodium reacts with oxygen to form sodium oxide, Na₂O.

Write a balanced symbol equation for this reaction. [2]

Give the formulae of the two ions in the white solid. [1]

(d) Sodium is stored under oil.

Suggest why. [1]

(a) sodium reacts with oxygen / air (to form a layer of sodium oxide) allow sodium oxidises; ignore 'tarnishes' alone (restates the question)(1)
(b) $\text{Na} + \text{O}_2 \rightarrow \text{Na}_2\text{O}$ (correct formulae)(1)
(b) balanced: $4\text{Na} + \text{O}_2 \rightarrow 2\text{Na}_2\text{O}$ allow multiples / fractions, e.g. $2\text{Na} + \tfrac{1}{2}\text{O}_2 \rightarrow \text{Na}_2\text{O}$; ignore state symbols(1)
(c) Li⁺ and Cl⁻ (both needed, charges required) do not accept Cl₂⁻ or Cl²⁻(1)
(d) to stop it reacting with oxygen / water (vapour) in the air allow keeps air / moisture away from the sodium; ignore 'to keep it safe'(1)
Answer: (a) reacts with oxygen to form sodium oxide (b) 4Na + O₂ → 2Na₂O (c) Li⁺ and Cl⁻ (d) stops it reacting with oxygen / water vapour in air
Examiner tip: Oxygen is diatomic: write O₂, not O, then balance — a common slip is 2Na + O₂ → Na₂O, which leaves an O atom unaccounted for.

7Grade 4–55 marks

The table gives some information about the Group 1 elements.

Element	Melting point in °C	Density in g/cm³
lithium	181	0.53
sodium	98	0.97
potassium	63	0.86
rubidium	?	1.53
caesium	28	1.93

(a) Predict the melting point of rubidium. [1]

(b) Describe the trend in melting point going down Group 1. [1]

A student says: “All Group 1 metals float on water.”

Use the data to explain why the student is not correct. [2]

(d) Caesium reacts with chlorine.

Give the formula of the compound formed. [1]

(a) any value between 29 °C and 62 °C (actual value 39 °C)(1)
(b) (melting point) decreases (going down the group) allow gets lower(1)
(c) rubidium and caesium have densities greater than (1.00 g/cm³) / greater than water allow correct reference to either rubidium or caesium with its density(1)
(c) so they would sink (in water) ignore 'they would not react' / references to reactivity(1)
(d) CsCl do not accept CsCl₂ or CSCL(1)
Answer: (a) about 40 °C (any value 29–62 °C) (b) decreases (c) Rb (1.53) and Cs (1.93) are denser than water, so they would sink (d) CsCl
Examiner tip: Use the numbers: say which metals have a density above 1.00 g/cm³ — just saying 'some are heavier' does not score.

8Grade 6–75 marks

The bar chart shows the boiling points of four halogens.

(a) Calculate the relative formula mass ($M_r$) of bromine, Br₂.

Relative atomic mass ($A_r$): Br = 80 [1]

(b) Use the bar chart to give the boiling point of iodine. [1]

(d) Explain why the boiling points of the halogens increase going down Group 7. [2]

(a) 160(1)
(b) any value from 180 °C to 190 °C (chart drawn at 184 °C)(1)
(c) fluorine and chlorine (both needed) allow F₂ and Cl₂(1)
(d) the molecules get larger / relative formula mass increases (going down the group) allow more electrons / more shells(1)
(d) so the intermolecular forces are stronger and more energy is needed to overcome them do not accept covalent bonds broken (max 1 if covalent bonds are said to break)(1)
Answer: (a) 160 (b) about 184 °C (c) fluorine and chlorine (d) larger molecules, so stronger intermolecular forces need more energy to overcome
Examiner tip: Boiling a halogen separates molecules — it never breaks the covalent bond inside Br₂; mentioning covalent bonds breaking loses the second mark in (d).

9Grade 8–9Higher7 marks

Chlorine reacts with potassium iodide solution.

$$\text{Cl}_2(\text{aq}) + 2\text{KI}(\text{aq}) \rightarrow 2\text{KCl}(\text{aq}) + \text{I}_2(\text{aq})$$

(a) Write the ionic equation for this reaction. [2]

(b) Complete the half equation for the chlorine in this reaction.

$\text{Cl}_2 + \ldots\ldots \rightarrow \ldots\ldots$ [1]

(d) A student adds excess chlorine to a solution containing 3.32 g of potassium iodide.

Calculate the maximum mass of iodine that could be produced.

Relative atomic masses ($A_r$): K = 39, I = 127 [3]

(a) $\text{Cl}_2 + \text{I}^- \rightarrow \text{Cl}^- + \text{I}_2$ (correct species, with no K⁺) allow K⁺ shown on both sides (spectator ions) for this mark only(1)
(a) balanced: $\text{Cl}_2 + 2\text{I}^- \rightarrow 2\text{Cl}^- + \text{I}_2$ ignore state symbols; allow multiples(1)
(b) $\text{Cl}_2 + 2\text{e}^- \rightarrow 2\text{Cl}^-$ allow e for e⁻(1)
(c) (each chlorine atom / chlorine) gains (an) electron(s) do not accept chlorine gains oxygen / loses electrons; ignore references to oxidation state(1)
(d) $M_r$ KI = 166 and moles KI = 3.32 ÷ 166 = 0.020 (mol)(1)
(d) moles I₂ = 0.020 ÷ 2 = 0.010 (mol) allow ecf from incorrect moles of KI(1)
(d) mass I₂ = 0.010 × 254 = 2.54 (g) allow ecf from incorrect moles of I₂; correct answer with no working scores 3 marks; 5.08 g scores 2 (mole ratio not used)(1)
Answer: (a) Cl₂ + 2I⁻ → 2Cl⁻ + I₂ (b) Cl₂ + 2e⁻ → 2Cl⁻ (c) chlorine gains electrons (d) 2.54 g
Examiner tip: Two moles of KI make only one mole of I₂: forgetting to halve gives 5.08 g, and using $M_r$ = 127 instead of 254 for I₂ is the other common error.

10Grade 6–76 marks

A student is given these solutions:

chlorine water
bromine water
iodine solution
potassium chloride solution
potassium bromide solution
potassium iodide solution

Plan an investigation the student could do to find the order of reactivity of chlorine, bromine and iodine.

In your answer you should describe the results you would expect and explain how they show the order of reactivity. [6]

add a few drops of each halogen solution to separate samples of each of the other potassium halide solutions (e.g. in test tubes or on a spotting tile)(1)
do not mix a halogen with its own halide (e.g. chlorine water with potassium chloride) / use the same volumes each time(1)
observe / record any colour change in a results table(1)
chlorine water + potassium bromide: solution turns orange / yellow (bromine displaced)(1)
chlorine water + potassium iodide: solution turns brown (iodine displaced)(1)
bromine water + potassium iodide: solution turns (darker) brown (iodine displaced)(1)
bromine water + potassium chloride and iodine solution + either salt: no change / no reaction(1)
a colour change shows the halogen added is more reactive than the halogen in the salt (a displacement reaction)(1)
chlorine displaces both bromine and iodine so it is the most reactive; iodine displaces neither so it is the least reactive(1)
order: chlorine > bromine > iodine(1)
safety: wear eye protection / gloves; use a fume cupboard or well-ventilated room (halogens are toxic)(1)

Level	Marks	What it looks like
Level 3	5–6	A clear, logically sequenced method that another student could follow, using all three halogens with the halide solutions they could displace, with the expected colour changes linked to a correct order of reactivity.
Level 2	3–4	A workable method with most combinations tested and some expected observations, but the link from the results to the order of reactivity is incomplete or some steps are missing.
Level 1	1–2	Isolated relevant points, e.g. mixing a halogen with a salt solution or stating that chlorine is most reactive, without a method that would give the order.
No relevant content	0	No relevant content.

Answer: Mix each halogen with the other two halide solutions and look for a colour change: Cl₂ turns KBr orange and KI brown; Br₂ turns KI brown; iodine causes no change. Order: chlorine > bromine > iodine.
Examiner tip: Colour changes are only half the story — top-level answers say what each change means (which halogen was displaced) and use it to justify the order.

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