CAIE A-Level Chemistry AS 11.3 Some Reactions of the Halide Ions Questions

Practise halide reducing-strength trends, silver-ion tests and reactions with concentrated sulfuric acid.

Exam points

rank halide reducing strength and connect it to displacement or concentrated-acid redox
identify AgCl, AgBr and AgI from precipitate colour and their different behaviour with aqueous ammonia
write acid–base and redox equations for solid halides reacting with concentrated sulfuric acid

Covered syllabus points

11.3.1—Reactivity of halide ions as reducing agents 11.3.2—Reactions of halide ions

[Maximum number: 2]

The chlorides of some of the Period 3 elements are shown in Table 2.1.

Table 2.1

An excess of $\mathrm{Cl}^{-}(\mathrm{aq})$ is added to $1 \mathrm{~cm}^{3}$ of $\mathrm{Br}_{2}(\mathrm{aq})$ .

Describe what is observed. Explain your answer.

M1 orange colour (of solution) remains / no visible reaction
bromine $/ \mathrm{Br}_{2}$ cannot oxidise chloride/Ct

OR

bromine $/ \mathrm{Br}_{2}$ is not a strong enough oxidising agent (to oxidise chloride/Cl-)

[Maximum number: 2]

The Group 17 elements are oxidising agents.

Table 1.2 shows some information about reactions of $\ce{NaCl}$ , $\ce{NaBr}$ and $\ce{NaI}$ .

Table 1.2

Suggest an identity for the species that produces each observation in the reaction of NaI with concentrated $\mathrm{H}_{2} \mathrm{SO}_{4}$ .
black solid
yellow solid
effervescence

M1 black solid = iodine / $\ce{I2}$ AND yellow solid = sulfur / $\ce{S(8)}$

M2 effervescence = hydrogen sulfide $/ \mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})$

[Maximum number: 8]

Sodium halide salts react with concentrated sulfuric acid at room temperature.

(a)

Write an equation to represent the reaction of NaCl(s) with concentrated sulfuric acid.

[ 1 ]

$\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{NaHSO}_{4}+\mathrm{HCl}$

OR
$2 \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+2 \mathrm{HCl}$

(b)

Name this type of reaction.

[ 1 ]

(c)

NaI(s) reacts with concentrated sulfuric acid, at room temperature, to form steamy fumes.

[ 3 ]

(i)

Identify the chemical responsible for the steamy fumes.

[ 1 ]

(ii)

The reaction of NaI(s) with concentrated sulfuric acid continues, forming several other products, including a dark grey solid.

Identify the chemical responsible for the dark grey solid and one other product of this further reaction.
dark grey solid
other product

[ 2 ]

dark grey solid $\mathrm{I}_{2}$ / iodine

other product S / sulfur $\mathrm{OR} \mathrm{H}_{2} \mathrm{~S}$ / hydrogen sulfide OR $\mathrm{H}_{2} \mathrm{O}$ / water / steam

(d)

Explain the differences in observations, at room temperature, when NaI(s) reacts with concentrated sulfuric acid compared to those for NaCl(s).

[ 2 ]

(e)

Complete the equation for the reaction of $\mathrm{Br}^{-}$ with excess concentrated $\mathrm{H}_{2} \mathrm{SO}_{4}$ at room temperature.

[ 1 ]

$2 \mathrm{Br}^{\leftarrow}+2 \mathrm{H}^{+}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Br}_{2}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{SO}_{2}$

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question 3

Question (a)

Question (b)

Question (c)

Question (i)

Question (ii)

Question (d)

Question (e)