Salt preparation

Question 1

When to use precipitation?

Answer 1

Making insoluble salts.

Question 2

How to conduct precipitation?

Answer 2

1. Add 25.0cm3 of an appropriate soluble salt into a beaker, then add the other appropriate soluble salt into the beaker slowly.
2. Stir to mix the mixture and stop adding the second salt when reaction ceases (no more precipitation forms).
3. Filter the precipitate, rinse and dry with filter paper.

Question 3

When to use titration?

Answer 3

Making Group 1 / ammonium salts (SPA)

Question 4

How to conduct titration?

Answer 4

1. Pipette 25.0cm3 of an appropriate alkali into a conical flask. Add 2 drops of an appropriate pH indicator.
2. Titrate the alkali and indicator mixture with an appropriate acid from a burette, until end point is reached.
3. Repeat the titration with the same volume of the same acid and alkali, but without the pH indicator.
4. Heat the solution to evaporate off most of the water, until the solution becomes saturated. Cool the hot saturated solution to room temperature for crystals to form.
5. Filter the mixture, rinse the crystals and dry with filter paper.

Question 5

When to react acid with excess metal?

Answer 5

Ca - Pb salts

Question 6

When to react acid with excess insoluble bases (oxides / hydroxides) or carbonates?

Answer 6

Ca - Pt salts
Particularly from H+ onwards, cannot directly react acid with excess metal.

Question 7

Describe procedure of mixing dilute acid with excess metal to form salt.

Answer 7

1. Add dilute ___ acid to excess powder (metal).
2. When reaction ceases, filter off the excess metal.
3. Heat the filtrate to evaporate off most of the water, then cool the hot saturated solution to room temperature for crystals to form.
4. Filter the mixture, rinse the crystals and dry with filter paper.

Question 8

Describe procedure of mixing dilute acid with excess insoluble metal oxide / hydroxide to form salt.

Answer 8

1. Add dilute ___ acid to excess (metal base).
2. When reaction ceases, filter off the excess insoluble (metal base).
3. Heat the filtrate to evaporate off most of the water, then cool the hot saturated solution to room temperature for crystals to form.
4. Filter the mixture, rinse the crystals and dry with filter paper.

metal oxide / hydroxide + acid —> salt + water

Question 9

Describe the procedure of reacting acid with excess insoluble metal carbonate to form salt.

Answer 9

1. Add dilute ___ acid to excess (metal carbonate).
2. When reaction ceases, filter off the excess insoluble (metal carbonate).
3. Heat the filtrate to evaporate off most of the water, then cool the hot saturated solution to room temperature for crystals to form.
4. Filter the mixture, rinse the crystals and dry with filter paper.

Metal carbonate + acid —> salt + water + carbon dioxide

Question 10

Solubility of nitrates

Answer 10

All soluble

Question 11

Solubility of grp I metal salts

Answer 11

All soluble

Question 12

Solubility of ammonium salts

Answer 12

All soluble

Question 13

Solubility of sulfates

Answer 13

All soluble except Ca2+, Ba2+, Pb2+ and Ag+

Ag+ is debatable, only slightly soluble

Question 14

Solubility of chlorides, bromides, iodides

Answer 14

All soluble except Pb2+ & Ag+

Question 15

Solubility of carbonates

Answer 15

All insoluble (except Group 1 Metals & ammonium)

Question 16

Solubility of oxides & hydroxides

Answer 16

All insoluble except Ca2+, Ba2+, Sr2+ (and Group 1 Metals & ammonium)