Topic 16 - Inorganic Chemistry

Question 1

Precipitates

Answer 1

When two solutions are mixed, sometimes an insoluble solid is formed

Question 2

How to make soluble salts that do not contain Li+, Na+, K+ or NH4+

Answer 2

OXIDE/HYDROXIDE

1) heat tube acid in a water bath (will speed up the rate of reaction) in a time cupboard to avoid releasing acid fumes
2) mix metal oxide/hydroxide with acid, making sure to use excess to ensure all the acid has been used up
2) stir
3) filter out excess solid
4) heat filtrate gently using a Bunsen burner, to reduce the volume of the solution (as it cools, solubility drops and crystals form)
5) leave it to evaporate (if unsure, filter again to ensure no water is left)
6) dry crystals of moisture with filter paper
7) CuSO4 (aq) + 5H2O -> CuSO4•5H2O

Question 3

How to make insoluble salts

Answer 3

PRECIPITATION

1) mix the substances in a beaker
2) stir
3) filter off the precipitate (residue will still contain unwanted water and salt)
4) wash the precipitate with water to remove salt
5) dry the precipitate using filter paper to remove H2O

Question 4

How to make soluble salts that do contain Li+, Na+, K+, NH4-

Answer 4

TITRATION

1) do titration (tells you the volumes of acid and alkali needed)
2) mix these volumes of acid and alkali WITHOUT the indicator so it won’t be contaminated
3) heat (to reduce volume of solution, causing it to be saturated so that as it cools, solubility drops and crystals form)
4) leave to evaporate (if unsure, you can filter again to ensure that all of the water is gone)
5) dry moisture off crystals using filter paper

Question 5

How to choose your salts for precipitation

Answer 5

Both most be soluble

Both must contain one of the substances you want in your outcome

Question 6

Describe how to make lead sulphate

Answer 6

1) add 1 spatula of lead nitrate into a test tube. Add deionised water to dissolve it. Shake it to make sure all of the lead nitrate has dissolved. In a separate test tube, do the same with magnesium sulphate.
2) tip the two solutions into a small beaker, stir. Lead sulphate precipitates out.
3) put a folded piece of filter paper into a filter funnel and place this into a conical flask
4) pour the contents of the beaker into the middle of the filter paper, making sure the solution doesn’t go above the filter paper
5) swill out the beaker with more deionised water. And pour this into the filter paper (to make sure you get all of the precipitate from the beaker)
6) rinse the contents of the filter paper with deionised water to make sure that all of the soluble magnesium nitrate has been washed away
7) scrape the lead sulphate into fresh filter paper and leave it to dry in an oven