Making Salts

Question 1

You can make soluble salts using a _____ or an _________ base.

Answer 1

Metal, or an insoluble base, or an alkali.

Using an alkali is different though, you’ll see why.

Question 2

Name the steps required in making a soluble salt.

Answer 2

1) Add the metal, metal oxide or hydroxide to the acid.
The solid will dissolve in the acid as it reacts.
2) Filter out the excess metal, metal oxide, or metal hydroxide to get the salt solution.
3) To get pure crystals, evaporate some of the water present (makes solution more concentrated), then evaporate the rest very slowly, this is crystallisation.

Question 3

How will you know when all of the acid has been neutralised?

Answer 3

The excess metal oxide, metal oxide or metal hydroxide will sink to the bottom of the flask.

Question 4

To recap, what is an alkali?

Answer 4

A soluble base, it’ll dissolve in water.

Question 5

When making a soluble salt using an alkali, you have to be very ________ when adding the alkali to the acid.

Answer 5

Accurate.

Question 6

Why do you have to be careful when adding the alkali to the acid you’re trying to neutralise?

Answer 6

Because if you’re adding an acid to an alkali, you can’t filter out what’s left because they’re both liquids. You need to see when the reaction takes place, using an indicator.

Question 7

After you’ve determined how much alkali will neutralise the acid, using your indicator, what do you then do?

Answer 7

Repeat the experiment again using the exact same amount of acid and alkali, but without the indicator because the indicator would contaminate your salt.

Question 8

Once you’ve got an indicator-free solution of acid & alkali, what do you do?

Answer 8

Evaporate the solution to crystallise the salt.

Question 9

To make an insoluble salt, you use which type of reaction? Remember that insoluble means that it doesn’t dissolve in water.

Answer 9

Use a precipitation reaction.

Question 10

How do you produce insoluble salts? Method.

Answer 10

1) Pick 2 solutions that contain the ions you need (example, to make lead chloride, you need lead ions and chloride ions).
2) Mix lead nitrate solution (lead ions) with sodium chloride solution (chloride ions) to make the solid precipitate of Lead Chloride and aqueous Sodium Nitrate.
3) Filter the solution to remove the sodium nitrate, this leaves you with the solid precipitate of lead chloride.

Question 11

What’s a good use of precipitation reactions?

Answer 11

To remove poisonous ions from drinking water. Calcium and Magnesium ions make water hard, so you remove them using a precipitation reaction.