Flame Test Fireworks

Why it matters

Every festival sky is a chemistry exam: the gold, the brick-red, the peacock green of fireworks are metal ions shouting their names in colour. Shrink the same trick onto a platinum wire, and you can name the metal hiding in an unknown white salt.

Predict first

A firework bursts brick-red, and the colour flickers — it comes and goes. Which metal is packed inside?

Brick-red that is fugitive — it comes and goes — is calcium's signature. Sodium burns a persistent golden-yellow, potassium lilac, and copper a peacock bluish-green.

• Sodium
• Calcium — correct
• Copper
• Potassium

What you do

Clean the platinum wire in conc. HCl, pick up a speck of each salt, and hold it in the non-luminous flame. Match each metal ion to the colour it paints.

Check yourself

Before each flame test, the platinum wire is dipped in concentrated hydrochloric acid and heated until it adds no colour to the flame. Why?

Conc. HCl converts stray salts on the wire into volatile chlorides that burn away. The wire is ready only when it imparts no colour of its own to the flame.

Why does each metal paint the flame its own colour?

Each element has its own ladder of energy levels, so the light released when excited electrons drop back has a colour unique to that metal — a fingerprint in light.

An unknown salt gives a persistent golden-yellow flame; viewed through blue glass, the colour vanishes completely. The metal in the salt is:

Persistent golden-yellow that blue glass wipes out is the textbook identification of sodium. Blue glass filters sodium's yellow, which is how chemists spot other metals hiding behind sodium's glare.

• To clean the wire, so traces of old salts cannot show false colours — correct
• To make the flame burn hotter
• Because the acid itself glows with a bright colour
• Heat excites the metal's electrons to higher energy levels; as they fall back they emit light of a fixed, characteristic colour — correct
• The metal burns into a coloured oxide that tints the flame
• The flame simply reflects the natural colour of the metal
• Potassium
• Sodium — correct
• Calcium