Adapting a multistep chemical procedure for making a pure dry salt | Combined science

Starter quiz

What is a pure salt formed in a chemical reaction?

two reactants of the reaction

two products of the reaction

the salt that has been made dissolved in water

a solid sample of the salt that has been made ✓
The chemical reaction between an acid and a metal oxide, which makes a salt and water, is an example of a ______ reaction.

'neutralisation' ✓
How do we know for sure that the reaction between an acid and an insoluble metal oxide is complete?

there is no fizzing

there is some insoluble metal oxide on the bottom of the reaction vessel

pH paper dipped into the solution shows pH7 ✓

the colour of solution does not change when more insoluble metal oxide is added
What is the general name given to a solid caught in filter paper after a filtration?

'residue' ✓
Evaporating water from a salt solution to leave a pure salt is called ______.

'crystallisation' ✓
Match the following words, used to describe how to make pure salt samples, to their definitions.

crystallisation

⇔

forming solid crystals from saturated solution by evaporating solvent ✓

filtration

⇔

a technique to separate insoluble solids from a liquid mixture ✓

insoluble

⇔

when a substance does not dissolve in a particular solvent ✓

neutralisation

⇔

reaction of acid and base, producing solution of metal salt and water ✓

precipitate

⇔

an insoluble solid formed when two solutions react together ✓

What is the pH of a base?

less than 7

exactly 7

close to 7

more than 7 ✓
What are the products of a reaction between a metal carbonate and an acid?

salt + water

salt + water + carbon dioxide ✓

salt + water + hydrogen carbonate

salt + water + metal
What are the main steps required to produce a pure salt when reacting a soluble base (alkali) with an acid?

crystallisation ✓

distillation

filtration

heating

neutralisation ✓
What are the main steps required to produce a pure salt when reacting an insoluble base with an acid?

crystallisation ✓

distillation

filtration ✓

heating

neutralisation ✓
Adding an insoluble base to an acid in ______ helps make sure that all of the acid has reacted to produce a neutral solution.

'excess' ✓
What helps to ensure that the salt produced in a reaction between an insoluble base and an acid is very pure?

using pH paper to confirm the solution made is neutral ✓

testing the melting point of the salt produced

washing all glassware with distilled water before use ✓

adjusting the pH by adding acid drop by drop near the neutralisation point

avoiding overfilling filter paper ✓

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Gently heating the acid speeds up the reaction, ensuring all acid reacts.
The salt should be dried using an appropriate method (using filter paper, or in the oven).
A pure sample should be prepared with equipment washed with distilled water to avoid contamination.
Reacting a metal hydroxide with an acid also produces a salt and water.
Reacting a metal carbonate with an acid can produce a desired salt with water, as well as carbon dioxide gas.

Pupils can sometimes mistake the excess base for the salt formed as it is a solid.

Emphasise at the beginning of the experiment what soluble means and that the salt will be initially obtained dissolved in water.

Method - Describes how an experiment is carried out; it is a step-by-step procedure.
Apparatus - A piece of equipment that is designed for a particular use.
Evaluate - To evaluate something is to make a judgement about it with respect to a particular purpose.
Adapt - To make suitable for use or purpose, e.g. equipment or steps in an experimental procedure.