Sometimes in conjunction with flame tests, you can use sodium hydroxide to test for the presence of positive metal ions. This works because most ions with a +2 or +3 charge are insoluble in water. Therefore, when sodium hydroxide is added to a solution containing them, a hydroxide precipitate forms, containing the insoluble metal.

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We can identify positive ions in different compounds or solutions by using a flame test. In a flame test, the flame will change colour depending on the ions present in the substance you’re testing.

Below is a table of different positive ions and their respective colour:

Metal Colour
Lithium Crimson
Sodium Yellow
Potassium Lilac
Calcium Red
Barium Green

One potential issue with flame tests is that if there is more than one ion present, one colour could mask another. This is why you should also test with sodium hydroxide.