TEST FOR CATIONS

What are cations

Positively charged ion

What are the two groups of tests for cation

Flame test

Metal hydroxide test

What is the procedure of a flame test

Clean platinum wire loop by dipping in dilute HCL

Rinse in distilled water

Heat over Bunsen burner

Dip wire loop into sample compound

Put loop in clear blue part of Bunsen flame

See what colour flame turns as compound burns

What colour flame does Lithium produce

Crimson

What colour flame does Sodium produce

Yellow

What colour flame does Potassium produce

Lilac

What colour flame does Calcium produce

Orange-red

What colour flame does Copper produce

Green

What are the **(5)** cations tested for through flame tests

Lithium

Sodium

Potassium

Calcium

Copper

What is the limitation of flame tests

If there are 2 or more different metals, flame colours will together, confusing our results

What is the procedure of metal hydroxide tests

React metal ions w/ solution of sodium hydroxide

See what colour the solution turns

Why are metal hydroxide tests possible

Some metals ions form coloured precipitates when they react w/ hydroxide ions

Coloured precipitates determine colour of solution

What colour precipitate does Calcium form

White precipitate

What colour precipitate does Iron (II) form

Green precipitate

What colour precipitate does Iron (III) form

Brown precipitate

What colour precipitate does Magnesium form

White precipitate

What colour precipitate does Aluminium form

White at first, excess NaOH dissolves to form a colourless solution

Why is the wire loop cleaned

So there are no impurities

What properties must the wire have in flame tests

High melting point

Unreactive