Food and other products are tested for purity and safety by chemicals. There are two main types:
Qualitative analysis: investigates the kind of substances present in a sample.
Quantitative analysis: measures the amount of each substance present.
Water often contains ionic compounds, to identify these ions tests must be carried out.
One of these tests are flame tests, each ion gives off different colours to detect them.
Calcium creates a brick red colour.
Sodium a yellow colour
Potassium creates lilac colour.
Copper creates a greeny bluey colour.
To test for other cations, sodium hydroxide is added to the solution and a precipitate reaction occurs.
Aluminium creates a white precipitate
Calcium creates a white precipitate
Copper creates a pale blue precipitate
Iron 2 creates a green precipitate
Iron 3 creates a brown, rust precipitate
determine between aluminium and calcium
Aluminium and calcium can be determined by adding excess sodium hydroxide.
The calcium will remain unchanged.
The aluminium ion dissolves into a cloudless solution.