3.06 Making soluble salts

Question 1

STate two ways in which you can make soluble salts

Answer 1

1. By reacitng an acid with a metal or an insoluble base [i.e. a metal oxide/hydroxide/carbonate)
2. By reacting an acid with an alkali

Question 2

Give an equation to show how you can make copper chloride from copper oxide

Answer 2

2HCl (aq) + CuO (s) —-> CuCl2 (aq) + H2O (l)

Question 3

Give an equation to show how you can make copper sulfate from copper oxide

Answer 3

H2SO4 (aq) + CuO (s) —-> CuSO4 (aq) + H2O (l)

Question 4

Describe an experiment to make copper sulfate from copper oxide

Answer 4

1. Put sulfuric acid in a beaker and gentle warm in water bath (to speed up the reaction later). DO this in a fume cupboard (so acid fumes aren’t released into the room)
2. Add copper oxid to the acid, and stir
3. Keep adding copper oxide until it is in excess (you will know this as the insoluble oxide will sink to the bottom and not disappear - this shows that all the acid has been neutralised). Note: it is important the base is in excess to ensure there is no lefover acid in the product
4. Filter out excess copper oxide (filter paper and funnel)
5. To crystallise the copper sulfate in solution, heat with a Bunsen and an evaporating dish (this makes the solution more concentrated)
6. Leave the solution to cool. Blue crystals of hydrated CuSO4 will form and they can be filtered and dried

Question 5

Describe an experiment to make a soluble salt from an acid and alkali

Answer 5

Note: this experiment is trickier as you cannot add excess alkali to the solution, as this will contaminate the product

1. Measure set amount of acid into a conical flask using pipette
2. Add a few drops of indicator and place flask on white tile (so you can see colour changes easily). Note use an indicator with a single colour change (like methyl orange or phenophthalein) - universal indicator colour change is too gradual
3. Fill a burette with alkali and record the volume
4. Slowly add alkali to the acid, and swirl the flask regularly until the indicator suggests the solution is neutral
5. Record the final volumne of alkali left in the burette, then calculate the volume of alkali required in the neutralisation
6. Repeat steps 1-5 with the exact same volumes but without adding indicator (so you can make uncontaminatied salt)
7. Slowly evaporate some of the water from the solution and leave to cool so salt can crystallise. Then filter and dry to leave pure dry salt.