Making Salts

Question 1

Solubility Rule: Sodium, Potassium, Ammonium Salts

Answer 1

All common sodium, potassium, and ammonium salts are soluble.

Question 2

Solubility Rule: Nitrates

Answer 2

All nitrates are soluble.

Question 3

Solubility Rule: Chlorides

Answer 3

Most chlorides are soluble, except silver chloride and lead(II) chloride.

Question 4

Solubility Rule: Sulfates

Answer 4

Most sulfates are soluble, except barium sulfate, calcium sulfate, and lead(II) sulfate.

Question 5

Solubility Rule: Carbonates

Answer 5

Most carbonates are insoluble, except those of sodium, potassium, and ammonium.

Question 6

Solubility Rule: Hydroxides

Answer 6

Most hydroxides are insoluble, except those of sodium, potassium, and ammonium.

Question 7

What is a precipitation reaction?

Answer 7

A reaction where two soluble salts react to form an insoluble salt (a precipitate).

Question 8

How to make an insoluble salt?

Answer 8

React two soluble salts to form an insoluble salt and a soluble by-product.

Question 9

Example of making an insoluble salt

Answer 9

Mix lead nitrate and magnesium sulfate to make lead sulfate (insoluble).
Equation: Pb(NO₃)₂ + MgSO₄ → PbSO₄ (s) + Mg(NO₃)₂

Question 10

How to make a soluble salt using an acid and an insoluble base

Answer 10

React an acid with an insoluble base (e.g. a metal oxide or hydroxide).
Example: CuO + H₂SO₄ → CuSO₄ + H₂O

Question 11

How to make a soluble salt using a titration?

Answer 11

React an acid with an alkali using a titration to avoid excess reactants.

Question 12

Why use titration for soluble salts (acid + alkali)?

Answer 12

You can’t see when the reaction is finished and can’t add excess alkali — so titration ensures no contamination.

Question 13

Making Insoluble Salts (Example: Lead Sulfate)

Answer 13

1. Add 1 spatula of lead nitrate to a test tube, add deionised water, and shake to dissolve.
2. In another test tube, dissolve 1 spatula of magnesium sulfate in deionised water.
3. Mix the two solutions in a small beaker and stir; lead sulfate will precipitate out.
4. Fold filter paper, place in a funnel over a conical flask.
5. Pour the mixture into the filter paper carefully to avoid solids running down the sides.
6. Rinse the beaker with deionised water and pour into the funnel to collect all precipitate.
7. Rinse the precipitate with deionised water to wash away soluble magnesium nitrate.
8. Scrape the lead sulfate onto fresh filter paper and dry it in an oven or desiccator.

Question 14

Making Soluble Salts Using Acid and Insoluble Base

Answer 14

1. Heat the acid gently in a water bath (in a fume cupboard).
2. Add an insoluble base (metal oxide/hydroxide) to the acid until excess solid sinks (base is in excess).
3. Filter off excess solid to get a solution of salt and water.
4. Heat the solution gently to evaporate some water.
5. Leave solution to cool and crystallise.
6. Filter off the crystals and dry them.

Question 15

Making Soluble Salts Using Acid and Alkali (Titration Method)

Answer 15

1. Use a pipette to measure a set volume of acid into a conical flask.
2. Add a few drops of indicator (phenolphthalein or methyl orange).
3. Slowly add alkali from a burette until the indicator shows the endpoint (colour change).
4. Repeat the reaction using the exact volumes but no indicator to avoid contamination.
5. The resulting solution contains pure salt and water.
6. Gently evaporate some water and allow the salt to crystallise.
7. Filter and dry the pure salt crystals.