Introducing Chemical Reactions (OCR GCSE Chemistry A (Gateway))

Higher Only

An element, X, is reacted with oxygen, O₂.

• There is one product. It is the oxide of X, X oxide.

• 4.86 g of X reacts with 3.20 g of oxygen to make 8.06 g of X oxide.

i) Calculate the number of moles of X, oxygen and X oxide in the reaction. 

• Relative atomic mass of X = 24.3

• Relative formula masses: O₂ = 32.0; X oxide = 40.3.

Number of moles of X = ………………………………….

Number of moles of O₂ = ………………………………….

Number of moles of X oxide = ..................................................

[3]

ii) Use your answer to (i) to write the balanced symbol equation for the reaction between X and oxygen to make X oxide.

 [2]

Higher Only

The equation shows the reaction between sodium hydroxide and dilute sulfuric acid.  

Calculate the mass of sodium hydroxide needed to make 30.0 g of sodium sulfate.

Give your answer to 3 significant figures.

Answer = …………………………………. g

Magnesium burns in oxygen to make magnesium oxide.

The reaction involves both oxidation and reduction.

2Mg (s) + O₂ (g) → 2MgO (s)

magnesium + oxygen → magnesium oxide

Complete the sentences.

During this reaction, the oxidising agent is .....................................

The reducing agent is ........................................................

Higher Only

Magnesium has an atomic number of 12.

 Calculate the mean mass of an atom of magnesium.

 Quote your answer to 3 significant figures. 

• Avogadro constant = 6.022 × 10²³ atoms per mole

Answer = …………………………………. g

Higher Only

Copper oxide can be reduced to copper by reaction with hydrogen.

CuO + H₂ → Cu + H₂O

A reaction mixture contains 1.59 g of copper oxide and 0.20 g of hydrogen.

1.27 g of copper and 0.36 g of water are made.

Calculate the number of moles of each substance to determine the limiting reactant in this reaction.

Explain your choice.

The relative atomic mass of Cu is 63.5, of O is 16 and of H is 1.

Number of moles of CuO = ....................

Number of moles of H₂ = ....................

Number of moles of Cu = ....................

Number of moles of H₂O = ....................

The limiting reactant is .................... because ............................................................

A student investigates the thermal decomposition of copper carbonate.

copper carbonate → copper oxide + carbon dioxide

Here is the set-up of the apparatus she uses.

The student measures the mass of copper carbonate at the start of the experiment. She then measures the mass of copper oxide made.

She does the experiment five times using a different mass of copper carbonate each time.

Look at her results.

i) Plot a graph of the student’s results and draw a line of best fit.

[4]

ii) What is the mass of copper carbonate that needs to be heated to produce 2.50 g of copper oxide?

Use your graph in your answer.

Mass of copper carbonate = ....................................................... g [1]

iii) The mass of copper oxide made in the reaction is less than the mass of the copper carbonate heated.

Suggest why.

[1]

Higher Only

Calcium carbonate thermally decomposes to make calcium oxide and carbon dioxide.

 CaCO₃ → CaO + CO₂

Calculate the mass of calcium carbonate needed to make 209 g of calcium oxide.
(A_r: Ca = 40.1, C = 12.0, O = 16.0)

Give your answer to 3 significant figures.

 Mass of calcium carbonate = .................... g

Higher Only

The value of the Avogadro constant is 6.02 × 10²³.

What is meant by the Avogadro constant?

Higher Only

Calculate the number of water molecules in 72 g of water, H₂O.

Give your answer to 3 significant figures.

Higher Only

A student is reacting magnesium oxide with nitric acid.

 Look at the equation for the reaction.

 MgO + 2HNO₃ → Mg(NO₃)₂ + H₂O

 The student wants to make 14.8 g of magnesium nitrate, Mg(NO₃)₂.

 Calculate the masses of magnesium oxide and nitric acid that he needs.

 Mass of magnesium oxide needed = .................... g

 Mass of nitric acid needed = .................... g