Preparation of Salts

Question 1

what is the method for preparation of INSOLUBLE salts

Answer 1

precipitation method

Question 2

what are the methods for preparation of SOLUBLE salts

Answer 2

• acid + excess metal
• acid + insoluble oxide/carbonate
• acid + alkali (titration)

Question 3

describe precipitation method

Answer 3

1. add solution A to solution B

2. filter, wash and dry b/w filter papers

Question 4

describe acid + excess metal method

Answer 4

1. add excess metal to acid
2. filter of excess
3. crystallise solution (Hot Cat Fools Donkey)
4. heat to obtain saturated solution
5. cool to allow crystals to form
6. filter, wash, dry

Question 5

describe acid + insoluble oxide/carbonate method

Answer 5

1. add insoluble oxide/carbonate to acid
2. filter of excess
3. crystallise solution (Hot Cat Fools Donkey)
4. heat to obtain saturated solution
5. cool to allow crystals to form
6. filter, wash, dry

Question 6

describe acid + alkali titration method

Answer 6

1. titrate 25cm^3 of acid with alkali using an indicator
2. record the volume of alkali used
3. repeat titration without the use of indicator, but using the same volume of alkali
4. crystallise…

Question 7

why can other methods be used for insoluble salts

Answer 7

other methods will produce a skin of insoluble salt around the solid reagent, stopping the reaction
resulting in low yield, and forming a solid mixture

Question 8

what method(s) can be used for:
NH4+
K+
Na+

Answer 8

method 3:

acid + alkali titration

Question 9

what method(s) can be used for:
Ca2+
Mg2+
Al3+
Zn2+
Fe2+, Fe3+

Answer 9

methods 1 and 2:
acid + excess metal
acid + insoluble oxide/carbonate

Question 10

what method(s) can be used for:
Sn2+
Pb2+
Cu2+
Hg2+
Ag+

Answer 10

method 2

acid + insoluble oxide/carbonate

Question 11

what method(s) cannot be used for, and why:
NH4+
K+
Na+

Answer 11

cannot mtd 1: too reactive –> explosive reaction with acid

cannot mtd 2: oxides/carbonates are soluble –> excess will dissolve to form mixture/contamination

Question 12

what method(s) cannot be used for, and why:
Ca2+
Mg2+
Al3+
Zn2+
Fe2+, Fe3+

Answer 12

cannot mtd 3: the alkali solution does not exist + hydroxides are insoluble

Question 13

what method(s) cannot be used for, and why:
Sn2+
Pb2+
Cu2+
Hg2+
Ag+

Answer 13

cannot mtd 1: too unreactive –> no/slow reaction

cannot mtd 3: the alkali solution does not exist + hydroxides are insoluble