[Maximum number: 2]

Gallium is an element in Group 13.
A sample of gallium is analysed using a mass spectrometer. The mass spectrum produced is shown.

(a)

Calculate the relative atomic mass of gallium in this sample. Give your answer to 4 significant figures.

Show your working.
relative atomic mass =

[ 2 ]

(a)

An alkene, a carboxylic acid and a ketone, all of similar volatility, are mixed together. The mixture is then analysed by gas chromatography.

The gas chromatogram produced is shown.

The separation of the three compounds depends on their relative solubilities in the liquid stationary phase. The liquid stationary phase is an alkane.

[ 3 ]

(i)

Complete the table to suggest which compound in the mixture is responsible for each peak J, K and L. Explain your answer by reference to the intermolecular forces of each compound.

A student calculates the areas underneath the three peaks in the chromatogram.

[ 2 ]

(ii)

The area underneath each peak is proportional to the mass of the respective compound.

Calculate the percentage by mass in the original mixture of the compound responsible for peak K.
\% of mixture responsible for peak K =

[ 1 ]

[Maximum number: 1]

Copper is used in electrical equipment. It has a melting point of $1085^{\circ} \mathrm{C}$ .

(a)

The relative isotopic masses and natural abundances of the two isotopes in a sample of copper are shown in Table 1.1.

Table 1.1

(i)

Calculate the relative atomic mass, $A_{\mathrm{r}}$ , of copper in this sample using the data in Table 1.1.

Show your working.

A_{r}=

(b)

The mass spectrum of a sample of pure copper is shown in Fig. 1.1.

Fig. 1.1

Identify the ion with an abundance of 23 % in the sample.

[ 1 ]

(a)

Chloride ions can be identified using aqueous silver nitrate, $\mathrm{AgNO}_{3}(\mathrm{aq})$ .

\mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq}) \rightarrow \mathrm{AgCl}(\mathrm{~s})

0.303 g of a chloride of sulfur is completely hydrolysed with water. All the chlorine atoms present in the chloride of sulfur are converted into chloride ions. The solution is diluted to $100.0 \mathrm{~cm}^{3}$ .
A $25.00 \mathrm{~cm}^{3}$ sample of this solution is titrated with $0.0500 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{AgNO}_{3}(\mathrm{aq})$ . The titration requires $22.40 \mathrm{~cm}^{3}$ of $0.0500 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{AgNO}_{3}(\mathrm{aq})$ .

Calculate the empirical formula of the chloride of sulfur. Show all your working.

[ 3 ]

(a)

The number of moles of water of crystallisation in a hydrated ionic salt can be determined by titration using aqueous EDTA ${ }^{4-}$ ions with a suitable indicator.
- 0.255 g of hydrated chromium(III) sulfate, $\mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3} \cdot n \mathrm{H}_{2} \mathrm{O}$ , is dissolved in water and made up to $100 \mathrm{~cm}^{3}$ in a volumetric flask.
- $25.0 \mathrm{~cm}^{3}$ of this solution requires $26.2 \mathrm{~cm}^{3}$ of $0.00800 \mathrm{moldm}^{-3}$ aqueous EDTA ${ }^{4-}$ ions to reach the end-point.

The reaction occurs as shown.

\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}+\text { EDTA }^{4-} \rightarrow[\mathrm{CrEDTA}]^{-}+6 \mathrm{H}_{2} \mathrm{O}

Use the data to calculate the value of n in the formula of $\mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3} \cdot n \mathrm{H}_{2} \mathrm{O}$ .
Show your working.

n=

[ 3 ]

(a)

Bromine exists naturally as a mixture of two stable isotopes, ${ }^{79} \mathrm{Br}$ and ${ }^{81} \mathrm{Br}$ , with relative isotopic masses of 78.92 and 80.92 respectively.

[ 3 ]

(i)

Using the relative atomic mass of bromine, 79.90, calculate the relative isotopic abundances of ${ }^{79} \mathrm{Br}$ and ${ }^{81} \mathrm{Br}$ .

[ 3 ]

(a)

A sample of oxygen exists as a mixture of three isotopes. Information about two of these isotopes is given in the table.

[ 1 ]

(i)

Calculate the abundance of the third isotope.
abundance = \%

[ 1 ]

(ii)

The relative atomic mass of this sample of oxygen is 16.0044 .

Calculate the mass number of the third isotope. You must show your working.

mass number =

(a)

A sample of strontium, atomic number 38, gave the mass spectrum shown. The percentage abundances are given above each peak.

[ 1 ]

(i)

Explain why there are four different peaks in the mass spectrum of strontium.

[ 1 ]

(a)

The relative atomic mass of an element can be determined using data from its mass spectrum.

The mass spectrum of element X is shown, with the percentage abundance of each isotope labelled.

[ 2 ]

(i)

Use the data in the mass spectrum to calculate the relative atomic mass, $A_{\mathrm{r}}$ , of X. Give your answer to two decimal places and suggest the identity of X.
$A_{r}$ of X identity of X

[ 2 ]

(a)

An aldehyde, an alkane and a carboxylic acid, all of similar volatility, are mixed together. The mixture is then analysed in a gas chromatograph.

The gas chromatogram produced is shown.

The separation of the compounds depends on their relative solubilities in the stationary phase. The stationary phase is a liquid alcohol.

[ 1 ]

(i)

A student calculates the areas underneath the three peaks in the chromatogram.

The area underneath each peak is proportional to the mass of the respective compound.
Calculate the percentage by mass in the original mixture of the compound responsible for peak Z.
\% of mixture responsible for peak Z =

[ 1 ]

(b)

(i)

The mass spectrum of bromochloromethane, $\mathrm{CH}_{2} \mathrm{BrCl}$ , has a molecular ion peak, M , at an m / e value of 128. It also has M+2 and M+4 peaks.

Suggest the identity of the molecular ions that give rise to these peaks.
M peak
M+2 peak
M+4 peak

[ 2 ]

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