Salt Preparation

Question 1

What are the methods of salt preparation?

Answer 1

1. Ionic precipitation
2. Acids+bases/carbonates/metals (ABCM)
3. Titration

Question 2

When should ionic precipitation be used?

Answer 2

1. To produce insoluble salts
2. Both reactants aquaeous or one gas one aquaeous

Question 3

When should ABCM be used?

Answer 3

1. To produce soluble salts
2. Metal/base/carbonate added to acid must be insoluble
3. To prepare salts that are not from group I or ammonium salts

Question 4

When should titration be used?

Answer 4

1. To produced soluble salts
2. Both reactants and products must be soluble
3. To prepare group I or ammonium salts

Question 5

Why must the reactant with acid in ABCM reactions be in excess?

Answer 5

To ensure that all the acids are reacted completely and the only remaining substances are the solid reactant, and the solution containing the salt

Question 6

How can ABCM reactions be sped up and what is a precaution?

Answer 6

The acid can be warmed.
However only acids with insoluble bases/ moderately reactive metals should be warmed

Question 7

Example question:
How can you prepare a pure, dry sample of zinc nitrate salt? Acid: Nitric acid, zinc metal.

Answer 7

1. Add excess zinc metal to dilute nitric acid until no more can dissolve
2. Filter the mixture to obtain the filtrate which contains the zinc nitrate salt and to remove the excess zinc metal
3. Heat the mixture till it is saturated
4. Allow the mixture to cool and crystals to form
5. Filter the mixture to obtain the crystals
6. Wash the crystals with a small amount of cold distilled water
7. Dry the crystals between pieces of filter paper

Question 8

Why must the reactants be in exact volumes in a titration reaction?

Answer 8

Both reactants and the salt are soluble, so the end result will be contamintated with no way to separate the salt and the reactant

Question 9

Example question:
How can you prepare a pure, dry sample of sodium chloride? HCL, NaOH

Answer 9

Titration procedure
1. Fill up the burette with dilute hydrochloric acid
2. Note the initial burette volume
3. Pipette 25 cm3 of aqueous sodium hydroxide into a conical flask
4. Add a few drops of methyl orange into the conical flask. The solution turns from colourless to yellow
5. Add dilute hydrochloric acid from the burette slowly into the conical flask until one drop of the acid changes the colour of the indicator from yellow to orange which is the end-point
6. Note the volume of the burette
7. The volume of acid used is V1-V2

Preparing the salt
1. Repeat the experiment by pipetting 25 cm3 of aqueous sodium hydroxide into the conical flask and adding the calculated amount of hydrochloric acid without adding indicator
2. Evaporate the sodium chloride solution to dryness and obtain the residue left after evaporation

Question 10

Example question:
How can you prepare a pure, dry sample of lead (II) iodide salt? Lead (II) nitrate, aqueous sodium iodide

Answer 10

1. React aqueous lead (II) nitrate and aqueous sodium iodide together until no more precipitate forms
2. An insoluble precipitate, lead (II) iodide is formed
3. Filter the mixture to obtain the residue, lead (II) iodide
4. Wash the residue with large amounts of distilled water
5. Dry the residue between pieces of filter paper