GCSE Science | Reacting Masses

• moles = mass/ Mr
• this can also be remembered as mass = MrMoles
• work out the mass, moles and Mr of one part of the equation
• use the moles ratio to work out the moles of another part of the equation

Question 1

What mass of hydrogen is produced when 192 g of magnesium is reacted with hydrochloric acid?

Mg  +  2 HCl  →  MgCl₂  +  H₂ (3 marks)

Question 2

What mass of oxygen is needed to react with 8.5 g of hydrogen sulphide (H₂S)?

2 H₂S  +   3 O₂  →  2 SO₂  +  2 H₂O (3 marks)

Question 3

What mass of potassium oxide is formed when 7.8 g of potassium is burned in oxygen?

4 K   +   O₂   →   2 K₂O (3 marks)

Question 4

Railway lines are welded together by the Thermitt reaction, which produces molten iron.  What mass of iron is formed from 1 kg of iron oxide?

Fe₂O₃  +  2 Al  →  2 Fe  +  Al₂O₃ (3 marks)

Question 5

What mass of oxygen is required to oxidise 10 g of ammonia to NO?

4 NH₃  +  5 O₂  →  4 NO  +  6 H₂O (3 marks)

Question 6

What mass of aluminium oxide is produced when 135 g of aluminium is burned in oxygen?  

2 Al  +   3 O₂  →  Al₂O₃ (3 marks)