5.3.1 - Making Soluble Salts

Question 1

How do you make soluble salts !?

Answer 1

. We make soluble salts by neutralising acids and crystallising the resulting solution

Question 2

soluble salts equation:

Answer 2

Acid ➕ Base / Alkali ➡️ Salt ➕ Water
(Aq). (S). (Aq). (Aq). (l)

Question 3

Stage 1:
Making pure, dry crystals of a soluble salt

Answer 3

. First, you make the salt solution
- this is done using one of two methods , depending which salt you’re making

Question 4

What are the two methods used to make a salt solution !?

Answer 4

. The insoluble base method
. The titration method

Question 5

Stage 2:
Making pure, dry crystals of a soluble salt

Answer 5

. Second you crystallise the salt
- this is done in the same way regardless of method used in stage 1

Question 6

When is the insoluble base method used !?

Answer 6

. When making salts that don’t contain Na, K or NH4 ions

Question 7

Which acids are usually used in the insoluble base method !?

Answer 7

Usually one of:
. Hydrochloric acid (HCl)
. Sulfuric acid (H2SO4)
. Nitric acid (HNO3)

Question 8

Which base is usually used in the insoluble base method !?

Answer 8

. Usually a solid metal oxide

( you can also use a solid metal carbonate, the only difference is that you make some carbon dioxide, so there is fizzing during Stage 2)

Question 9

Step 1: insoluble base method

Answer 9

1. heat the acid

(Hot acid has not energy so it reacts faster with the base)

Question 10

Step 2: insoluble base method

Answer 10

2. While stirring add base until no more will dissolve

(This guarantees the base is in excess so that we know all the acid has been used up)

Question 11

Step 3: insoluble base method

Answer 11

. filter out the excess base

(Because you don’t want it)

Question 12

When is the Titration method used !?

Answer 12

. When making salts that contain Na, K or NH4 ions, as their bases are all soluble so you wouldn’t be able to filter out the excess if you used the insoluble base method

Question 13

Which acids are usually used in the Titration method !?

Answer 13

Usually one of:
. Hydrochloric acid (HCl)
. Sulfuric acid (H2SO4)
. Nitric acid (HNO3)

Question 14

Which alkali is used in the Titration method!?

Answer 14

. Usually one of:
- sodium hydroxide (NaOH)
- potassium hydroxide (KOH)
- ammonium hydroxide (NH4OH)

Question 15

Step 1: Titration method

Answer 15

. Perform a titration to measure the volumes of acid and alkali that neutralise each other

Question 16

Step 2: Titration method

Answer 16

. repeat the Titration, but this time:
- DON’T put the indicator in
- use the burette to add exactly the right volume for neutralisation

Question 17

What is the next step after you have made a salt solution !?

Answer 17

. You perform a crystallisation

Question 18

What is the purpose of performing crystallisation !?

Answer 18

. To get pure, dry salt crystals

Question 19

Step 1: Crystallisation

Answer 19

. heat the salt solution until salt crystals just start forming

(You can tell by looking at the edges)

(This causes the solution to become saturated)

Question 20

Step 2: Crystallisation

Answer 20

. Allow the solution to cool in an evaporating basin for a few days

(This lowers the solubility of the salt so that lots of solid crystals form)

Question 21

Step 3: Crystallisation

Answer 21

. filter out the crystals

(This removes them from the excess solution in the basin)

Question 22

Step 4: Crystallisation

Answer 22

. dry the crystals by dabbing them with filter paper

(This removes the last traces of water from the crystals)