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
This question is about chlorine and compounds of chlorine.
(a) Chlorine is an element in Group VII of the Periodic Table.
State the meaning of the term element.[1]
(b) State one use of chlorine.[1]
(c) Chlorine reacts with phosphorus to produce phosphorus(V) chloride.
(i) Balance the equation for this reaction.
…..P + …..Cl2 → 2PCl5 [2]
(ii) This reaction is exothermic.
State the meaning of the term exothermic.[1]
(d) Chlorine reacts with aqueous sodium bromide.
(i) Complete the word equation for this reaction.
(ii) Describe a test for bromide ions.[2]
test
observations
(iii) When bromine is mixed with aqueous sodium chloride there is no reaction.
Suggest in terms of chemical reactivity why there is no reaction.[1]
(e) A compound of chlorine has the formula C3H6Cl2.
Complete the table to calculate the relative molecular mass of C3H6Cl2.
relative molecular mass = [2] [Total: 12]
Answer/Explanation
Ans:
(a) substance containing only one type of atom / substance where the atoms have the same proton number
(b) water treatment / water purification / killing bacteria
c)(i) 2 (P) (1)
5 (Cl2) (1)
c)(ii) releases thermal energy / releases heat
(d)(i) bromine (1)
sodium chloride (1)
(d)(ii) (add nitric acid and aqueous) silver nitrate (1)
cream precipitate / cream solid (1)
(d)(iii) bromine is less reactive than chlorine / chlorine more reactive than bromine 1
(e) 113 (2)
If two marks not scored, allow 1 mark for H = 6 × 1 / 6 OR Cl = 2 × 35.5 / 71
Question
This question is about halogens and halogen compounds.
(a) Deduce the number of electrons, neutrons and protons in one atom of the isotope of chlorine shown.[3]
\(_{17}^{37}\textrm{Cl }\)
number of electrons
number of neutrons
number of protons
(b) State why chlorine is used in water treatment.[1]
(c) Aqueous chlorine reacts with aqueous potassium iodide.
(i) Complete the chemical equation for this reaction. [2]
Cl2 + …..KI → …..KCl + I2
(ii) Explain in terms of the reactivity of the halogens why aqueous iodine does not react with aqueous potassium chloride.[1]
(d) The table shows some properties of four halogens.
(i) Complete the table by predicting:
-
- the boiling point of fluorine
- the density of liquid chlorine at its boiling point. [2]
(ii) Predict the physical state of chlorine at –105°C.
Give a reason for your answer.[2] [Total: 11]
Answer/Explanation
Ans:
(a) electrons: 17 (1)
neutrons: 20 (1)
protons: 17 (1)
(b) to kill bacteria (1)
(c)(i) 2 (KI) (1)
2 (KCl) (1)
(c)(ii) chlorine is more reactive than iodine / iodine is less reactive than chlorine
(d)(i) boiling point of fluorine:
values between – 40 and – 210 (inclusive of these values) (1)
density of chlorine:
values between 1.6 and 3.0 (inclusive of these values) (1)
(d)(ii) solid (1)
–105 °C is lower than the melting point / the melting point is above –105 °C (1)