Making Soluble Salts

Question 1

What needs to react together to make a soluble salt?

Answer 1

An acid containing one of the ions you want in the salt, and an insoluble base that contains the other ion you need (often a metal oxide or metal hydroxide).

Question 2

What is the method for making soluble salts?

Answer 2

1) Start by heating the acid in a water bath - this speeds up the reaction between the acid and the insoluble base. Do this in a fume cupboard to avoid releasing acid fumes into the room.
2) Then add the base to the acid - the base and acid will react to produce a soluble salt (and water). You will know when the base is in excess and all the acid has been neutralised because the excess solid will sink to the bottom of the flask.
3) Filter off the excess solid to get a solution containing only the salt and water.
4) Heat the solution gently, using a Bunsen burner, to slowly evaporate off some of the water. Leave the solution to cool and allow the salt to crystallise. Filter off the solid salt and leave it to dry.

Question 3

What are soluble salts?

Answer 3

Salts that dissolve in water.

Question 4

How can you make soluble salts using acid/alkali reactions?

Answer 4

• Measure out a set amount of acid into a conical flask using a pipette. Add a few drops of indicator.
• Slowly add alkali to the acid, using a burette, until you reach the end point - this is when the acid’s been exactly neutralised and the indicator changes colour.
• Then, carry out the same using exactly the same volumes of alkali and acid but no indicator, so the salt isn’t contaminated by indicator.
• The solution that remains when the reaction is complete contains only the salt and water.
• Slowly evaporate off some of the water and then leave the solution to crystallise. Filter off the solid and dry it - you’ll be left with a pure, dry salt.