[Maximum number: 2]

Two groups of students (Group A and Group B) carried out a project* on the chemistry of some group 7 elements (the halogens) and their compounds.

(a)

In this project the students explored several aspects of the chemistry of the halogens. In the original preparation of $\operatorname{ICl}(1)$ , they observed the yellow-green colour of chlorine gas, $\mathrm{Cl}_{2}(\mathrm{~g})$ , reacting with solid iodine, $\mathrm{I}_{2}(\mathrm{~s})$ .

[ 2 ]

(i)

One important use of chlorine is in the synthesis of poly(chloroethene), PVC. Identify the monomer used to make PVC and state one of the uses of PVC.

Monomer:

Use:

[ 2 ]

[Maximum number: 2]

Alloys containing at least 60 % copper reduce the presence of bacteria on their surface. The percentage of copper in brass, an alloy of copper and zinc, can be determined by UV-vis spectrometry.

A sample of brass is dissolved in concentrated nitric acid and then made up to $250.0 \mathrm{~cm}^{3}$ with water before analysis.

\begin{aligned} & \mathrm{Cu}(\mathrm{~s})+4 \mathrm{HNO}_{3}(\mathrm{aq}) \rightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{NO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \\ & 3 \mathrm{Zn}(\mathrm{~s})+8 \mathrm{HNO}_{3}(\mathrm{aq}) \rightarrow 3 \mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{NO}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \end{aligned}

The concentration of copper(II) ions in the resulting solution is then determined from a calibration curve, which is plotted by measuring the light absorbance of standard solutions.

Calibration curve

(a)

(i)

Comment on the suitability of using brass of this composition for door handles in hospitals.

If you did not obtain an answer to (d)(i), use 70 % but this is not the correct answer.

[ 1 ]

(ii)

Suggest another property of brass that makes it suitable for door handles.

[ 1 ]

[Maximum number: 1]

Alloys containing at least 60 % copper reduce the presence of bacteria on their surface. The percentage of copper in brass, an alloy of copper and zinc, can be determined by UV-vis spectrometry.

A sample of brass is dissolved in concentrated nitric acid and then made up to $250.0 \mathrm{~cm}^{3}$ with water before analysis.

\begin{aligned} & \mathrm{Cu}(\mathrm{~s})+4 \mathrm{HNO}_{3}(\mathrm{aq}) \rightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{NO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \\ & 3 \mathrm{Zn}(\mathrm{~s})+8 \mathrm{HNO}_{3}(\mathrm{aq}) \rightarrow 3 \mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{NO}(\mathrm{~g})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \end{aligned}

The concentration of copper(II) ions in the resulting solution is then determined from a calibration curve, which is plotted by measuring the light absorbance of standard solutions.

Calibration curve

You may find the following chart and diagram helpful.

The electromagnetic spectrum energy

(a)

(i)

Suggest another property of brass that makes it suitable for door handles.

[ 1 ]

[Maximum number: 1]

Iron may be extracted from iron (II) sulfide, FeS.

(a)

Iron (II) sulfide, FeS , is ionically bonded.

[ 1 ]

(i)

Suggest why chemists find it convenient to classify bonding into ionic, covalent and metallic.

[ 1 ]

[Maximum number: 3]

Iron may be extracted from iron (II) sulfide, FeS.

(a)

Iron (II) sulfide, FeS, is ionically bonded.

[ 1 ]

(i)

Suggest why chemists find it convenient to classify bonding into ionic, covalent and metallic.

[ 1 ]

(b)

Explain why the addition of small amounts of carbon to iron makes the metal harder.

[ 2 ]

[Maximum number: 1]

Iron(II) sulfide can be produced by heating powdered iron and sulfur together.

(a)

Outline why solid iron(II) sulfide is a polar covalent compound. Use sections 9 and 17 of the data booklet.

[ 1 ]

[Maximum number: 2]

Titanium is a transition metal.

(a)

(i)

Explain why an aluminium-titanium alloy is harder than pure aluminium.

[ 2 ]

[Maximum number: 2]

Titanium and vanadium are consecutive elements in the first transition metal series.

(a)

(i)

Explain why an aluminium-titanium alloy is harder than pure aluminium.

[ 2 ]

[Maximum number: 1]

The electronegativities of four elements are given in the table.

Which statement is correct?

A

W and X form an ionic compound.

B

W and X form a covalent compound.

C

Y and Z form an ionic compound.

D

Y and Z form a covalent compound.

[Maximum number: 1]

Which compound is predominantly covalent?

A

LiCl

B

$\mathrm{Al}_{2} \mathrm{O}_{3}$

C

ClF

D

$\mathrm{ZnCl}_{2}$