Rules Of Solubility + Salt Preparation

Question 1

Soluble ionic compounds in water

Answer 1

• all nitrates
• common chlorides are soluble, except those of silver and lead(II)
• common sulphates are soluble, except those of barium, calcium and lead (II)

Question 2

Insoluble ionic compounds

Answer 2

• common carbonates, except sodium, potassium and ammonium
• common hydroxides, except sodium, potassium and calcium (calcium hydroxide is slightly soluble)

Question 3

Are nitrates soluble or insoluble?

Answer 3

Soluble

Question 4

Are chlorides soluble or insoluble?

Answer 4

Soluble (except silver and lead (II)

Question 5

Are sulphates soluble or insoluble?

Answer 5

Soluble (except those of barium, calcium, lead (II)

Question 6

Are carbonates soluble or insoluble?

Answer 6

Insoluble (except sodium, potassium and ammonium)

Question 7

Are hydroxides soluble or insoluble?

Answer 7

Insoluble (except sodium, potassium and calcium), calcium hydroxide is slightly soluble

Question 8

How to make an insoluble salt?

Answer 8

• to make a pure, dry sample of an insoluble salt, you can use a precipitation reaction
• react the right two soluble salts to get an insoluble salt

e.g. to make lead sulphate (insoluble), mix lead nitrate and magnesium sulphate (both soluble)

Question 9

Lead sulphate reaction

Answer 9

Lead nitrate + magnesium sulphate —> lead sulphate + magnesium nitrate

Question 10

Lead sulphate balanced equation

Answer 10

Pb(NO3)2 +MgSO —> PbSO4 +Mg(NO3)2
(aq) (aq) (s) (aq)

Question 11

Lead sulphate practical (paper 2)

Answer 11

1) add 1 spatula of lead nitrate to a test tube. Add water to dissolve it ( use deionised water to make sure there is no other ions about).
2) Shake thoroughly to ensure that all the lead nitrate has dissolved. Then in a separate test tube repeat the process with 1 spatula of magnesium sulphate
3) tip the two solution into a small beaker, and give it a stir to mix. The lead sulphate should precipitate out
4) still a filter funnel with filter paper in into a conical flask
5) pour the contents of the beaker into the middle of the filter paper
6) swill out the beaker with more deionised water, and top this into the filter paper to make sure you get all the precipitate from the beaker
7) scrape the lead sulphate onto fresh filter paper + leave it out to dry in an oven or desiccator

Question 12

How to make a soluble salt

Answer 12

• by reacting an acid that contains one of the ions you want in the salt with an insoluble base that contains the other ion you need (often a metal oxide or metal hydroxide)

Question 13

Making soluble salts experiment

Answer 13

1) heat acid in water bath - speeds up the reaction. Do this in a fume cupboard to avoid releasing acid fumes into the room
2) add base to acid - the base and acid will react to produce a soluble salt (and water). You will know when the base is in excess and all that acid has neutralised because the excess solid will just sink to the bottom of the flask
3) filter off the excess solid to get a solution containing only the salt and water
4) heat the solution gently, using a Bunsen burner, to slowly evaporate off some of the water
5) leave the solution to cool and allow the salt to crystallise
6) filter of the solid and leave it dry

Question 14

Example of a soluble salt experiment

Answer 14

• you can add copper oxide to warm sulphuric acid to make a solution of copper sulphate
• if you evaporate off some of the water and leave this solution to crystallise, you should get blue crystals of hydrated copper sulphate which you can filter off and dry

Question 15

Make copper sulphate equation

Answer 15

CuO + H2SO4 —> CuSO4 +H20
(s) (aq) (aq) (l)

Question 16

Why does the base need to be in excess?

Answer 16

So that there is no leftover acid in the product as then the final product would be simply a soluble salt and water

Question 17

How can soluble salts be made using acid/alkali reactions?

Answer 17

• soluble salts can be made by reacting an acid with an alkali
• however you can’t tell whether the reaction is finished - there’s no signal that all the acid has been neutralised. You can’t add excess alkali because the salt is soluble and would be contaminated
• titration with an indicator can be used to find the exact amount of alkali needed to neutralise the acid

Question 18

Making soluble salts with acids/alkalis experiment

Answer 18

1) measure out a set amount of acid into a conical flask using a pipette
2) add a few drops of indicator. For a titration you need a indicator with a single, clear colour change (like phenolphthalein or methyl orange). Universal indicators colour change is too gradual
3) slowly add alkali to the acid using a burette, until you reach the end point when the indicator changes colour + the acid is neutralised
4) then carry out the experiment using the exact same volumes of acid and alkali without an indicator so the salt won’t be contaminated
5) the solution that remains when the experiment is complete is only salt and water
6) slowly evaporate some of the water and leave solution to crystallise. Filter of the solid and dry it - you are left with a pure, dry salt