Conservation of mass and relative formula mass: practice

4 marksFoundation5.3.1.2 Relative formula mass

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.1.2
Original practice question
Answer and supported method checks

Relative atomic masses (

A_r

): H = 1, C = 12, O = 16, Mg = 24, Cl = 35.5

.1

Calculate the relative formula mass (

M_r

) of water,

\mathrm{H_{2}O}

.

[1 mark]

.2

Calculate the

M_r

of carbon dioxide,

\mathrm{CO_{2}}

.

[1 mark]

.3

Calculate the

M_r

of magnesium chloride,

\mathrm{MgCl_{2}}

.

[2 marks]

4 marksFoundation and Higher5.3.1.3 Mass changes when a reactant or product is a gas5.3.1.1 Conservation of mass and balanced chemical equations

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.1.3
Spec 5.3.1.1
Original practice question
Answer and supported method checks

A student heats 2.40 g of magnesium ribbon in an open crucible. It all reacts to form 4.00 g of magnesium oxide.

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

.1

Calculate the mass of oxygen that reacted with the magnesium.

[1 mark]

.2

The student says: "The mass went up, so mass was not conserved." Explain why the student is wrong.

[2 marks]

.3

The student repeats the experiment in a sealed container full of air and weighs the whole container. Predict what happens to the total mass.

[1 mark]

3 marksFoundation5.3.1.1 Conservation of mass and balanced chemical equations

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.1.1
Original practice question
Answer and supported method checks

Balanced equations show that atoms are not made or destroyed in a reaction.

.1

Balance the equation:

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

[1 mark]

.2

Balance the equation:

\mathrm{N_{2} + H_{2} \rightarrow NH_{3}}

[1 mark]

.3

Explain why you must not change the small numbers in a formula when balancing an equation.

[1 mark]

6 marksHigher5.3.1.4 Chemical measurements5.3.1.2 Relative formula mass

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.1.4
Spec 5.3.1.2
Original practice question
Answer and supported method checks

A student heats four samples of copper carbonate and measures the mass of copper oxide left each time. 4.03 g, 4.07 g, 3.59 g, 4.05 g

.1

Identify the anomalous result and give a reason.

[1 mark]

.2

Calculate the mean mass. Do not include the anomalous result.

[2 marks]

.3

Calculate the uncertainty in the mean, using the range of the three results you used.

[1 mark]

.4

Calculate the percentage by mass of copper in copper oxide, CuO. (

A_r

: Cu 63.5, O 16)

[2 marks]

4 marksFoundation and Higher5.3.1.2 Relative formula mass5.3.1.1 Conservation of mass and balanced chemical equations

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.1.2
Spec 5.3.1.1
Original practice question
Answer and supported method checks

Ammonium nitrate,

\mathrm{NH_{4}NO_{3}}

, is used as a fertiliser.

A_r

: H = 1, N = 14, O = 16

.1

Calculate the

M_r

of ammonium nitrate.

[2 marks]

.2

Calculate the percentage by mass of nitrogen in ammonium nitrate.

[2 marks]