chemistry - making salts

Question 1

how to prepare a sample of pure, dry copper sulfate crystals from a sample of insoluble copper oxide?

Answer 1

• react sulphuric acid with excess copper oxide
• filter to remove the excess copper oxide
• heat the solution to start evaporation
• turn off the heat and leave until all the water has evaporated
• you will be left with copper sulfate crystals

Question 2

write the chemical equation for the reaction between CuO and H2SO4

Answer 2

CuO + H2SO4 —> CuSO4 + H2O

Question 3

what safety precautions need to be considered when preparing a pure, dry salt from an insoluble compound?

Answer 3

• bunsen burner should be turned off or put on the safety flame when not in use
• sulphuric acid is corrosive so wear eye protection

Question 4

what are two methods of separating mixtures?

Answer 4

• filtration
• crystallisation

Question 5

how can you separate an insoluble product from a solution?

Answer 5

Filtration:
- filter paper placed in a funnel over a conical flask
- pour mixture through the funnel
- insoluble product left on the filter paper

Question 6

How to separate soluble solids from solutions?

Answer 6

evaporation:
- place the mixture in an evaporating dish
- slowly heat the dish
- the solvent evaporates and the solution becomes more concentrated so crystals will start to form
- keep heating the evaporating dish until you have dry crystals

Question 7

how can you separate a soluble solid from a solution, if the solid decomposes when heated?

Answer 7

Crystallisation:
- pour the solution into an evaporating dish and heat gently
- when the crystals start to form, remove the dish from the heat and leave to cool
- once cold, filter the crystals out of the solution and leave them in a warm place to dry