Knowledge Organiser: Flame Tests
Flame Colours
- Li⁺ = Crimson red
- Na⁺ = Orange-yellow
- K⁺ = Lilac/purple
- Ca²⁺ = Orange-red (brick red)
- Cu²⁺ = Blue-green
- Ba²⁺ = Yellow-green (apple green), not required by AQA or Edexcel
Method Steps
- Dip wire in dilute HCl
- Heat until no colour
- Dip in HCl then sample
- Hold in blue flame
- Observe colour immediately
Science Behind It
- Heat excites electrons to higher levels
- Electrons fall back to ground state
- Energy released as coloured light
- Each element has unique energy gaps → unique colour
Limitations
- Not all metals give colours
- Similar colours can be confused
- Sodium contamination common
- Blue glass needed for potassium
Key Equations
- No calculation equations — identification topic
- Li⁺ = crimson, Na⁺ = orange-yellow, K⁺ = lilac, Ca²⁺ = orange-red, Cu²⁺ = blue-green
- Mnemonic: Little Naughty Kids Can Be (Li Na K Ca Ba — in colour order)
Common Mistakes
- Confusing calcium and sodium flame colours: Calcium = orange-red (brick red); sodium = orange-yellow — they look similar but the yellow is much brighter for sodium
- Forgetting to clean the wire between tests: The wire must be cleaned with dilute HCl and heated until no colour appears — old sample contamination gives false results
- Saying potassium gives a purple flame: Potassium gives LILAC — it is a pale purple/violet; a strong purple is not the correct observation
- Thinking flame tests identify the anion: Flame tests only identify METAL CATIONS — they give no information about the anion (e.g. Cl⁻, SO₄²⁻)
Memory Aid
Learn the first letter of each metal and its colour: "Little Naughty Kids Catch Cats, Bright Ones!" Li = Red | Na = Yellow | K = Lilac | Ca = Orange-red | Cu = Green | Ba = Yellow-green Or remember it as: "LiRed, NaYellow, KLilac, CaOrange-red, CuGreen, BaYellow-green" For the method: "Dip, Heat, Dip, Sample, Flame" — always clean before and after. Quick Check: A flame test on an unknown compound produces an orange-yellow colour. Name the metal ion present. Show Answer Sodium ion (Na⁺). The orange-yellow colour is the characteristic flame colour for sodium.