2.1 Purity and separating mixtures

This question is about relative formula masses and formulae.

A model of a molecule of compound X has four carbon atoms, eight hydrogen atoms and two oxygen atoms.

Write the molecular formula and the empirical formula of compound X.

[2]

Compound Y has the empirical formula $C2H5\mathrm{C_{2}H_{5}}$ . The relative formula mass ( $M_{r}$ ) of Y is 58.0.

Deduce the molecular formula of Y.

Relative atomic masses ( $A_{r}$ ): C = 12.0, H = 1.0

[2]

c.i.

A metal carbonate has the formula $MCO3\mathrm{MCO_{3}}$ , where M is a metal. When it is heated, it decomposes.

\mathrm{MCO_{3} \rightarrow MO + CO_{2}}

The $M_{r}$ of $MCO3\mathrm{MCO_{3}}$ is 197.3.

Identify metal M.

[2]

c.ii.

Calculate the $M_{r}$ of MO.

[1]

Magnesium burns in oxygen.

\mathrm{2Mg + O_{2} \rightarrow 2MgO}

A student says, "The total $M_{r}$ of the reactants is 56.3, so the total $M_{r}$ of the products must also be 56.3."

Evaluate the student's statement.

Relative atomic masses ( $A_{r}$ ): Mg = 24.3, O = 16.0

[3]

2.1 Purity and separating mixtures Questions