Chemical Changes: Making Soluble Salts Required Practical

Question 1

How would you prepare a sample of pure, dry copper sulfate crystals from a sample of insoluble copper oxide?

Answer 1

1. Measure 25cm³ of sulfuric acid and 3 heaped spatulas of copper oxide into a beaker. Ensure copper oxide is in excess.
2. Stir with a stirrer.
3. Filter the excess copper oxide using filter paper and a funnel into a conical flask
4. Pour the filtrate (copper sulfate solution) into an evaporating basin.
5. Set up a Bunsen Burner with a tripod, gauze and heatproof mat.
6. Place a beaker of water onto the gauze and place the evaporating basin over this beaker. This removes the water from the solution and ensures it evaporates slowly allowing bigger crystals to form.
7. Pat crystals dry using a paper towel and scrape them from the dish using a spatula.

Question 2

Write the chemical equation for the reaction between CuO and H₂SO₄.

Answer 2

CuO_(s) +H₂SO_4(aq) → CuSO_4(s) + H₂O_(l)

Question 3

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

Answer 3

• Bunsen burner could burn you so should be turned off or put on the safety flame when not in use
• sulfuric acid is an irritant so wear eye protection
• using glassware which could cut you if it breaks so clean up with a dust pan and brush immediately
• copper oxide is damaging to the environment so dont pour it down the sink in raw form

Question 4

What are 2 methods of separating mixtures?

Answer 4

• filtration
• crystallisation

Question 5

How could you separate an insoluble soluble solid from a a solution if the solid decomposes when heated?

Answer 5

Crystallisation:
- pour the solution into an evaporating dish and heat gently (could heat it over a beaker of water or in a water bath)
- 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