5 This question is about salts
5-1 Name the salt produced by the neutralisation of hydrochloric acid with potassium hydroxide. [1 mark]
ANSWER
Potassium chloride
5-2 Write an ionic equation for the neutralisation of hydrochloric acid with potassium hydroxide. [1 mark]
ANSWER
H+ + OH− → H2O
5-3 Soluble salts can be produced by reacting dilute hydrochloric acid with an insoluble solid.
Copper, copper carbonate and copper oxide are insoluble solids.
5-4 Which of these insoluble solids can be used to make a copper salt by reacting the solid with dilute hydrochloric acid? [1 mark]
ANSWER
Copper carbonate and copper oxide only
A student makes crystals of magnesium sulfate.
This is the method used.
1. Add sulfuric acid to a beaker.
2. Warm the sulfuric acid.
3. Add a spatula of magnesium oxide to the beaker.
4. Stir the mixture.
5. Repeat steps 3 and 4 until there is magnesium oxide remaining in the beaker.
6. Filter the mixture.
7. Evaporate the filtrate gently until crystals start to form.
8. Leave the solution to finish crystallising.
5-5 Give one reason for:
step 2
step 5
Step 6. [3 marks]
ANSWER
Step 2: to speed up the reaction;
Step 5: to make sure all the HCl acid reacts;
Step 6: to remove the excess magnesium oxide
5-6 How should the filtrate be evaporated gently in step 7? [1 mark]
ANSWER
Using a boiling water bath or using an electric heater.
5-6 Iron chloride is produced by heating iron in chlorine gas. The equation for the reaction is:
2 Fe + 3 Cl2 → 2 FeCl3
Calculate the volume of chlorine needed to react with 14 g of iron. You should calculate:
the number of moles of iron used
the number of moles of chlorine that react with 14 g of iron
the volume of chlorine needed.
Relative atomic mass (Ar): Fe = 56
The volume of 1 mole of gas = 24 dm3 [3 marks]
ANSWER
Now by seeing the equation, the molar ratio of Fe:Cl2 = 2:3
Therefore one mole of iron reacts with
Therefore, 0.25 mol. of Fe will react with
