3.1 Introducing Chemical Reactions

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.

[4]

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

[1]

Higher Only

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

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.

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.

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.