[Maximum number: 3]

In the Periodic Table, the p block contains elements whose outer electrons are found in the p subshell.

(a)

Silicon is found in many compounds in the Earth's crust. Silicon has only three naturally occurring isotopes, ${ }^{28} \mathrm{Si},{ }^{29} \mathrm{Si}$ and ${ }^{30} \mathrm{Si}$ .

[ 3 ]

(i)

The table shows data for ${ }^{28} \mathrm{Si},{ }^{29} \mathrm{Si}$ and ${ }^{30} \mathrm{Si}$ .

A sample of silicon contains $92.2 \%{ }^{28} \mathrm{Si}$ . The total percentage abundance of ${ }^{29} \mathrm{Si}$ and ${ }^{30} \mathrm{Si}$ in the sample is 7.8 %.

The relative atomic mass, $A_{\mathrm{r}}$ , of silicon in the sample is 28.09 .
Calculate the percentage abundance of ${ }^{30} \mathrm{Si}$ .
Give your answer to one decimal place.
percentage abundance of ${ }^{30} \mathrm{Si}=$ \%

[ 3 ]

[Maximum number: 1]

Which sample contains the same number of the named species as the number of molecules in 35.5 g of chlorine?

A

atoms in 16 g of sulfur

B

atoms in 23 g of sodium

C

ions in 74.5 g of potassium chloride

D

molecules in 88 g of carbon dioxide

(a)

A sample of sulfur contains only two isotopes, ${ }^{32} \mathrm{~S}$ and ${ }^{34} \mathrm{~S}$ . The relative atomic mass of this sample is 32.09 .

Calculate the percentage abundance of the isotopes present in this sample.

\begin{aligned} & \% \text { abundance }{ }^{32} \mathrm{~S}= \\ & \% \text { abundance }{ }^{34} \mathrm{~S}= \end{aligned}

[ 3 ]

[Maximum number: 2]

Combustion data can be used to calculate the empirical formula, molecular formula and relative molecular mass of many organic compounds.

(a)

Define the term relative molecular mass.

[ 2 ]

[Maximum number: 1]

Which statement about the Avogadro constant is correct?

A

It is the mass of one mole of any element.

B

It is the mass of $6.02 \times 10^{23}$ atoms of any element.

C

It is the number of atoms in one mole of neon.

D

It is the number of atoms in 12 g of any element.

[Maximum number: 3]

Ethanedioic acid, $\mathrm{HO}_{2} \mathrm{CCO}_{2} \mathrm{H}$ , has a relative molecular mass of 90.0.

(a)

(i)

Calculate how many atoms of carbon are present in 0.18 g of ethanedioic acid, $\mathrm{HO}_{2} \mathrm{CCO}_{2} \mathrm{H}$ . Show your working.
atoms of carbon present =

[ 3 ]

(a)

(i)

The element copper has a relative atomic mass of 63.5.

Calculate how many atoms are present in 1.05 g of copper.

atoms of copper present =1]

[ 1 ]

[Maximum number: 2]

Atoms with nuclei containing an odd number of protons tend to have fewer isotopes than those with an even number of protons.

(a)

Gallium has two stable isotopes, ${ }^{69} \mathrm{Ga}$ and ${ }^{71} \mathrm{Ga}$ .

[ 2 ]

(i)

The relative atomic mass of gallium, $A_{r}$ , is 69.723.

The relative isotopic masses of ${ }^{69} \mathrm{Ga}$ and ${ }^{71} \mathrm{Ga}$ are:

{ }^{69} \mathrm{Ga}, 68.926 ;{ }^{71} \mathrm{Ga}, 70.925 .

Use this information to calculate the percentage abundance of ${ }^{69} \mathrm{Ga}$ in elemental gallium. Show your working.
Assume that the element contains only the ${ }^{69} \mathrm{Ga}$ and ${ }^{71} \mathrm{Ga}$ isotopes.
Give your answer to four significant figures.
percentage abundance of ${ }^{69} \mathrm{Ga}=$ \%

[ 2 ]

(a)

Most elements exist naturally as a mixture of isotopes, each with their own relative isotopic mass. The mass spectrum of an element reveals the abundances of these isotopes, which can be used to calculate the relative atomic mass of the element.

Magnesium has three stable isotopes. Information about two of these isotopes is given.

[ 3 ]

(i)

The relative atomic mass of magnesium is 24.3.

Calculate the percentage abundance and hence the relative isotopic mass of the third isotope of magnesium. Give your answer to three significant figures
percentage abundance =

[ 3 ]

(a)

Sodium chloride is traditionally added to a particular meat product. In response to the evidence that sodium chloride can lead to high blood pressure, the manufacturers have replaced the sodium chloride with a mixture of sodium and potassium chlorides. 100 g of the meat product usually contains about 2 g of the chloride mixture.
A particular meat product contains 1.10 g of sodium chloride and 0.90 g potassium chloride in 100 g .

(i)

Calculate the number of moles of chloride ions in 100 g of this meat product.

The amount of chloride in the meat product can be found by titration with silver nitrate solution.