Test for cations

An unknown salt produces a red flame during in a flame test. What cation does it contain?

• chloride

• lithium

• copper

• calcium

Why is a luminous flame not suitable for a flame test

• It is not hot enough

• It is too hot

• The colour may hide the flame colour from the salt

• It will only heat up the wire

Magnesium chloride is given a flame test what colour flame will you see?

Two salts have been accidentally mixed together. They contain potassium cations and copper cations. What colours will the flame show?

• Green and lilac

• Lilac and red

• Green and brick red

• Lilac and orange

• Green and Orange

A solution containing Iron(II) cations forms what colour precipitate when sodium hydroxide is added.

Some sodium hydroxide solution is accidentally spilt onto to some copper(II)sulphate solution. What would you expect to see?

• The copper(II)sulphate solution goes from blue to colourless

• A blue precipitate forms

• A green precipitate forms

• No change

A pupil suspects an unknown salt contains ammonium NH₄⁺ ions. They place some red litmus paper at the top of a test tube to test for ammonia gas but see no change. What steps did they forget for the test?

• Add some sodium hydroxide solution

• Heat the tube gently

• Putting the red litmus paper into the solid

• Nothing, the unknown salt must not have ammonium ions

An unknown salt produces an orange/yellow flame. What cation does it contain?

• sodium

• lithium

• potassium

• calcium

• copper

After adding sodium hydroxide to an unknown solution a red precipitate is formed. The solution contains which cation?

• Fe(II)

• Fe(III)

• Fe(V)

• Cu(II)

Why do we dip our wire into acid and then heat it when we are conducting flame test?

• To remove previous chemicals

• To stop contamination of colour from other chemicals

• To clean the wire

• To find out if the acid contains a metal cation