Making a Pure Salt Flashcards

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In chemistry, what does a “pure salt” mean?

A pure salt is a sample that only contains one salt compound, with no other substances mixed in.

What type of base is often used to make a pure soluble salt from an acid, and why?

We often use an insoluble base, such as a metal oxide or carbonate. Extra base can then be removed by filtration.

Why is the acid warmed gently before adding the insoluble base when making a pure salt?

Warming the acid speeds up the reaction. It also helps the salt dissolve in the water.

Why is the base added in excess (more than needed) to the warm acid?

Extra base makes sure that all the acid has reacted. This means no acid is left in the final salt solution.

After reacting the acid with an excess insoluble base, what separation method is used and what is removed?

We use filtration. It removes the extra solid base from the salt solution.

What name is given to the clear liquid that passes through the filter paper when making a pure salt?

The clear liquid is called the filtrate. It contains the dissolved salt in water.

What do we do with the filtrate to start forming salt crystals?

We heat it gently to evaporate some of the water. This makes the solution more concentrated so crystals can form.

Why should we stop heating the salt solution before all the water has boiled away?

We stop heating so some water is left. Then crystals form as the solution cools, instead of the salt breaking down.

How are salt crystals dried after they have formed?

We remove them with a spatula and pat them dry with filter paper. They can also be left in a warm place to dry.

Why is the salt made by this method considered pure?

All the acid has reacted and the extra base has been filtered off. Only the salt and water are left before the water is removed.

Which salt is formed if copper(II) oxide reacts with dilute sulfuric acid in this method?

The reaction makes copper sulfate, a blue crystal salt.

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