Question
This question is about iodine and compounds of iodine.
(a) Use the kinetic particle model to describe the separation between the molecules and the type of motion of the molecules in:
- solid iodine
- iodine gas. [4]
(b) The graph shows how the volume of iodine gas changes with pressure. The temperature is kept constant.
Describe how the volume of iodine gas changes with pressure.[1]
(c) (i) Complete the word equation to show the halogen and halide compound which react to form the products iodine and potassium bromide.
(ii) Explain, in terms of the reactivity of the halogens, why aqueous iodine does not react with aqueous potassium chloride
(d) lodine reacts with aqueous sodium thiosulfate, $\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3$.
(i) Balance the chemical equation for this reaction.
$
\mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3+\mathrm{I}_2 \rightarrow \mathrm{Na}_2 \mathrm{~S}_4 \mathrm{O}_6+\ldots . . \mathrm{NaI}
$
(ii) The energy level diagram for this reaction is shown.
Explain how this diagram shows that the reaction is exothermic [1]
(e) Describe a test for iodide ions.
test
observations[2]
(f) Molten sodium iodide is electrolysed.
Predict the product at the positive electrode.[1][Total: 14]
▶️Answer/Explanation
Ans:
(a) solid:
particles touching / particles close together (1)
particles (only) vibrating / not moving from place to place (1)
gas:
particles far apart (1)
particles moving fast / particles moving randomly / particles moving in any direction (1)
4(b) increasing the pressure decreases the volume / decreasing the pressure increases the volume / the higher the volume, the lower
the pressure
4(c)(i) bromine (1)
potassium iodide (1)
Question
The table shows some properties of four Group I elements.
(a) (i) Complete the table by estimating:
-
- the boiling point of sodium
- the relative hardness of lithium. [2]
(ii) Predict the physical state of lithium at 200°C.
Give a reason for your answer. [2]
(b) Potassium reacts with water.
2K + 2H2O → 2KOH + H2
Describe two observations when potassium reacts with water.[2]
1
2
(c) Lithium is extracted by the electrolysis of molten lithium chloride.
(i) Name a non-metal used to make the electrodes.[1]
(ii) Give one property, other than the conduction of electricity, that makes this substance suitable for use as an electrode.[1]
(iii) State the products of the electrolysis of molten lithium chloride at:[2]
the negative electrode (cathode)
the positive electrode (anode)
(d) Lithium chloride conducts electricity when molten and when in aqueous solution.
Give two other physical properties of lithium chloride that show it is an ionic compound.[2]
1
2 [Total: 12]
Answer/Explanation
Ans:
(a)(i) boiling point of Na any values between 800 and 1300 (°C) (inclusive of these values) (1)
hardness of Li: any value above 0.70 (MPa) up to a maximum of 5.0 (MPa) (1)
(a)(ii) liquid (1)
200 °C is above the melting point and below the boiling point / 200 °C is between the melting and boiling points (1)
(b) 1 mark each for any 2 of:
-
- bubbles / effervescence / fizzing
- potassium disappears
- potassium moves around
- potassium floats on the surface
- (bursts into) flame / sparks / explodes
BUT
colour of flame is lilac = 2 marks
(c)(i) carbon / graphite
(c)(ii) inert / unreactive
(c)(iii) negative electrode: lithium (1)
positive electrode: chlorine (1)
(d) high boiling point / high melting point (1)
soluble in water (1)
Question
This question is about zinc and compounds of zinc.
(a) Zinc is a metal.
Give three physical properties of metals.[3]
1
2
3
(b) Zinc reacts with phosphorus to form zinc phosphide, Zn3P2.
Complete the equation for this reaction.[2]
Zn + P → Zn3P2
(c) Molten zinc chloride is electrolyzed.
The incomplete apparatus is shown.
(i) Complete the diagram by:[2]
completing the circuit to show the wires and power pack
labelling the anode.
(ii) Name the products formed at each electrode.[2]
positive electrode
negative electrode
(d) Zinc chloride reacts with water as shown. The solution formed is acidic.
\(ZnCl_{2}+2H_{2}O\rightleftharpoons Zn\left ( OH \right )_{2}+2HCl\)
(i) State the meaning \(\rightleftharpoons\) of the symbol .[1]
(ii) Choose the pH value which is acidic.
Draw a circle around your chosen answer.[1]
pH 3 pH 7 pH 9 pH 14
(e) A compound of zinc has the formula ZnC4H10.
Complete the table to calculate the relative molecular mass of ZnC4H10.
relative molecular mass = [2] [Total: 13]
Answer/Explanation
Ans:
(a) 1 mark each for any three of:
-
- conduct electricity OR conduct heat (1)
- malleable (1)
- ductile (1)
- shiny / lustrous (1)
(b) 3 (Zn) (1)
2 (P) (1)
(c)(i) wires leading from each side of power pack or battery to the electrodes (1)
positive electrode labelled anode (1)
(c)(ii) positive electrode: chlorine (1)
negative electrode: zinc (1)
d)(i) reversible reaction
(d)(ii) pH 3
(e) 123 (2)
if two marks not scored, allow 1 mark for C = 4 x 12 / 48 OR H = 1 x 10 / 10