Flame tests

How do you carry out a flame test

• take a platinum/nichrome wire

• Dip into concentrated hydrochloric acid and then heat in bunsen flame until no colour is seen

• Dip wire into fresh concentrated hydrochloric acid then into metal salt

• Heat wire and sample in flame

Why do you use a nichrome/platinum wire?

They’re unreactive with the air in the flame and do not have their own flame colour

Why is the wire dipped into hydrochloric acid and then heated (the first time)

To clean the wire of any other previous samples

Why is the wire dipped in concentrated HCl then in the sample

It reacts with the salts to form chlorides which are more volatile as they have lower boiling points as they need to be in the gaseous state for the tests to work.

Li+

Red/crimson

Na+

Yellow

K+

Lilac

Rb+

Red

Cs+

Blue/violet

Be2+

Colourless

Mg2+

Colourless

Ca2+

Brick red

Sr2+

Red

Ba2+

Apple green

How do flame tests work

• electrons absorb the heat energy from the flame and move to higher energy levels

• Electrons drop back down to lower energy levels

• Light in visible region is released

• Different energy gaps between levels cause different colours