CP 3 ‐ Preparing Copper Sulfate

Question 1

How could you prepare pure, dry copper sulfate

crystals from copper oxide?

Answer 1

• React sulfuric acid with excess copper oxide
• Filter to remove the excess copper oxide
• Heat the filtrate to start evaporation
• Turn off the heat and leave until all the water has
  evaporated
• Left with copper sulfate crystals

Question 2

Why shouldn’t you evaporate all the water from the

copper sulfate solution using a Bunsen burner?

Answer 2

• The copper sulfate crystals would start
  to decompose if continually heated
• Hot copper sulfate crystals would spit
  out, this could damage skin and eyes

Question 3

Sulfuric acid is warmed in a water bath before the

copper oxide is added. Why?

Answer 3

The reaction is faster with warm acid.

This ensures all the acid reacts.

Question 4

Why is copper oxide added in excess to the sulfuric

acid when preparing pure copper sulfate crystals?

Answer 4

To ensure all the sulfuric acid reacts

Any excess copper oxide can be filtered out

Question 5

What is a base?

Answer 5

Any substance which reacts with an acid

to form salt and water only

Question 6

Write the chemical equation for the reaction between

CuO and H2SO4

Answer 6

CuO + H2SO4 → CuSO4

+ H2O

Question 7

What colour is CuSO4

(aq)?

Answer 7

Blue

Question 8

During filtration, what is the filtrate and what is the

residue?

Answer 8

Filtrate - the liquid that has passed
through the filter

Residue - the solid which remains in the
filter paper

Question 9

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

Answer 9

• Bunsen burner should be turned off or put on
  the safety flame when not in use,
• tie hair back,
• keep flammable chemicals away from the flame
• Sulfuric acid is corrosive so wear eye protection

Question 10

What are two methods of separating mixtures?

Answer 10

Any two from:

Filtration

Crystallisation

Evaporation

Question 11

How can you separate an insoluble

product from a solution?

Answer 11

Filtration:

• Place filter paper in a funnel over a conical flask
• Pour mixture through the funnel
• Insoluble product left on the filter paper

Question 12

How can you separate soluble solids from solutions?

Answer 12

Evaporation:

• Pour mixture into an evaporating basin
• Slowly heat the solution
• As the solvent evaporates, the solution becomes more
  concentrated so crystals start to form
• Keep heating the evaporating basin until you have dry
  crystals

Question 13

How could you separate a soluble solid from a

solution, if the solid decomposes when heated?

Answer 13

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.