Flame Test Worksheet
Name Class Date
Part A — Flame colours of metal ions
Complete the table with the colour each metal ion gives in a flame test.
1.
| Metal ion | Flame colour |
|---|---|
| Lithium, Li⁺ | Crimson (red) |
| Sodium, Na⁺ | Intense yellow-orange (persistent) |
| Potassium, K⁺ | Lilac (pale violet; pink-violet through cobalt-blue glass) |
| Calcium, Ca²⁺ | Brick red (orange-red) |
| Strontium, Sr²⁺ | Crimson / bright red |
| Barium, Ba²⁺ | Apple green (pale green) |
| Copper(II), Cu²⁺ | Blue-green |
Part B — Colour key
Shade each box with the flame colour (coloured pencils).
2.
Lithium, Li⁺
Sodium, Na⁺
Potassium, K⁺
Calcium, Ca²⁺
Strontium, Sr²⁺
Barium, Ba²⁺
Copper(II), Cu²⁺
Lithium, Li⁺ — Crimson (red)
Sodium, Na⁺ — Intense yellow-orange (persistent)
Potassium, K⁺ — Lilac (pale violet; pink-violet through cobalt-blue glass)
Calcium, Ca²⁺ — Brick red (orange-red)
Strontium, Sr²⁺ — Crimson / bright red
Barium, Ba²⁺ — Apple green (pale green)
Copper(II), Cu²⁺ — Blue-green
Part C — Identify the unknown
Use the flame colours (and any other information) to identify each metal ion. Give a reason.
3.
Salt W is white and gives an apple-green flame.
Ba2+ (barium) — apple-green flame. e.g. barium chloride.
4.
Salt X is blue and gives a blue-green flame.
Cu2+ (copper(II)) — blue-green flame; copper(II) salts are blue (e.g. CuSO4·5H2O).
5.
Salt Y gives a lilac flame that is only visible through cobalt-blue glass because a yellow colour is also present.
K+ (potassium) — lilac flame; the yellow is from sodium (impurity), filtered out by the blue glass.
6.
Salt Z gives a brick-red flame; its solution gives a white precipitate with ammonium oxalate.
Ca2+ (calcium) — brick-red flame, confirmed by white calcium oxalate precipitate.
7.
Two salts both give a red flame. Name the two metal ions that could be responsible and suggest how to tell them apart.
Li+ (crimson) and Sr2+ (crimson/scarlet). Distinguish with a confirmatory test — e.g. Sr2+ gives a white precipitate with ammonium sulfate, Li+ does not — or compare their line spectra with a spectroscope.
8.
Describe how to carry out a flame test, including how to clean the wire loop.
Dip a nichrome/platinum wire loop in concentrated HCl and heat in a blue (roaring) Bunsen flame until no colour is seen. Dip the clean loop in acid then the solid sample (or make a paste with conc. HCl) and hold it at the edge of the non-luminous flame. Observe the colour; clean between samples.
9.
Explain, in terms of electrons, why each metal ion produces a characteristic flame colour.
Heating excites electrons to higher energy levels. When they return to lower levels they emit photons whose energies (ΔE = hf) match the gaps between levels. Each element has unique energy levels, so it emits characteristic wavelengths — a characteristic colour.
10.
Why does the flame test fail to identify the metals in a mixture of sodium and potassium chloride without extra equipment?
The intense yellow sodium flame masks the faint lilac of potassium; cobalt-blue glass or a spectroscope is needed.
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