7.3 - Salts Preparation

Question 1

What is a salt? [3]

Answer 1

• a compound
• typically formed when a hydrogen ion of an acid
• is replaced by a metal ion or another positive ion

Question 2

How do we prepare, separate and purify soluble salts through acid with alkali titration? Outline the process. [7]

Answer 2

1. add a measured volume of alkali into a conical flask using a pipette
2. add a few drops of indicator to the alkali
3. add acid from a burette until the indicator changes colour
4. record the volume of acid used
5. heat the resulting neutralised solution in an evaporating basin to evaporate the water
6. allow the solution to cool and crystallise
7. drain the excess solution and allow the crystals to dry

Question 3

How do we prepare, separate and purify soluble salts through acid with excess metal? Outline the process. [6]

Answer 3

1. add a lot of metal to the acid in a beaker
2. metal dissolves and hydrogen gas bubble come out
3. allow the reaction to continue until no more gas is produced
4. this shows that all the acid has reacted with the metal
5. filter the mixture to remove any unreacted metal
6. evaporate the filtered solution to obtain the pure salt

Question 4

How do we prepare, separate and purify soluble salts through acid with excess insoluble base? Outline the process. [4]

Answer 4

1. add a lot of the insoluble base to the acid in a beaker
2. stir and heat the mixture until no more of the base dissolves
3. filter the mixture to remove any unreacted base
4. evaporate the filtered solution to obtain pure salt

Question 4

How do we prepare, separate and purify soluble salts through acid with excess insoluble carbonate? Outline the process. [4]

Answer 4

1. add a lot of the insoluble carbonate to the acid in a beaker
2. stir and heat the mixture until no more of the carbonate dissolves
3. filter the mixture to remove any unreacted carbonate
4. evaporate the filtered solution to obtain the pure salt

Question 5

What is the process called that we use to prepare insoluble salts? [1]

Answer 5

precipitation

Question 5

What is precipitation? [3]

Answer 5

• mixing two soluble salts in solution
• which react to form an insoluble salt
• that precipitates out of the solution

Question 5

How do we prepare, separate and purify insoluble salts through precipitation? Outline the process. [6]

Answer 5

1. separately dissolve the known amounts of the two soluble salts in distilled water in separate beakers
2. mix the two solutions together
3. the insoluble salt will precipitate out of the solution as a solid
4. filter the mixture to separate the precipitate from the liquid solution
5. wash the precipitate with distilled water to remove any remaining soluble impurities
6. dry the purified precipitate in an oven

Question 6

What are anhydrous substances? [1]

Answer 6

• a substance containing no water

Question 7

What is a hydrated substance? [1]

Answer 7

• a substance that is chemically combined with water