making salts

Acids react with metals, bases and carbonates to produce salts. In this practical, you will react sulfuric acid with insoluble copper (II) oxide to prepare an aqueous solution of the salt copper sulfate. You will separate unreacted copper (II) oxide by filtration and follow steps to evaporate the solvent to obtain a pure dry sample of copper sulfate crystals.

aim

prepare a pure, dry sample of a soluble salt from an insoluble oxide or carbonate

equipment

• copper oxide base

• sulfuric acid

steps

1. take a measured amount e.g. 40cm³ of acid using measuring cylinder

2. pour into beaker

3. gently heat using a tripod, gauze and bunsen burner for a short period of time

4. remove beaker from heat and add excess copper oxide

5. once copper oxide is in excess, must remove this from copper sulfate so crystals are pure - filter using filter paper and funnel, pour beaker contents into paper

6. pure, blue copper sulfate solution passes through to conical flask

7. evaporate the water using an evaporating basin

8. heat evaporating basin - place it on a beaker of boiling water on the tripod above a bunsen burner

9. as crystals begin to form, stop heating and leave crytals to cool so more form

10. scrape crystals out, leave to dry in warm oven/dab with filter paper

how do you know when copper oxide is in excess?

no more colour changes (here, mixture is blue when not in excess and black in excess as there is black unreacted copper oxide present)

no more bubbling/effervescence occurs