A-LevelChemistryGroup 179701/21 · May/June 2024 · Q110 Marks

The elements of Group 17 are called halogens.

(a)Complete Table 1.1. Table 1.1 halogen | colour at 293 K chlorine | bromine | iodine | [1]
(b)State the trend in volatility of the halogens chlorine, bromine and iodine. Explain your answer.[3]
(c)(i)Iodine is made by reacting bromine with sodium iodide. Construct an ionic equation for the reaction of bromine with sodium iodide.[1]
(c)(ii)State the role of bromine in the reaction. Explain your answer.[1]
(d)Concentrated sulfuric acid is added to separate samples containing equal amounts of NaCl, NaBr and NaI. All three samples initially react to produce the hydrogen halide.
(d)(i)Write an equation to describe the acid-base reaction that occurs when concentrated sulfuric acid reacts with NaBr.[1]
(d)(ii)Deduce which sodium halide, NaCl, NaBr or NaI, produces the largest percentage yield of hydrogen halide when concentrated sulfuric acid is added. Explain your answer by considering the relative reactivity of the halide ions as reducing agents. identity of sodium halide explanation[3]

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[1] All three correct for one mark
chlorine green
bromine brown
iodine (dark) grey
[3] M1 (it/volatility) decreases
M2 more electrons in molecules
M3 (so) increased strength of instantaneous dipole – induced dipole forces (of attraction)
[1] Br2 + 2I → 2Br¯ + I2
[1] (Br2/bromine is an) oxidising agent
AND
removes electron(s) from iodide (ions) I- OR increases the oxidation number of I-/ iodide (ion)
[1] NaBr + H2SO4 → HBr + NaHSO4
OR
2NaBr + H2SO4 → 2HBr + Na2SO4
[3] M1 sodium chloride
M2 Cl- is not a strong enough reducing agent to reduce H2SO4
M3 Br- & I- are strong enough reducing agents to react (further) with (the S in) H2SO4
Alternative M2 and M3
M2 ability to behave as reducing agents increases down the group
M3 EITHER Cl- is not strong enough to reduce H2SO4 OR Br- and I react (further) with (the S in) H2SO4

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