This higher tier covers Higher Tier: The Blue Glass Technique within Flame Tests for GCSE Chemistry. Revise Flame Tests in Chemical Analysis for GCSE Chemistry with 22 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 10 of 13 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
🎓 Higher Tier: The Blue Glass Technique
Blue glass is used when testing for potassium because:
- Even tiny traces of sodium produce an intensely bright yellow-orange that masks the faint lilac of potassium
- Blue glass acts as a colour filter — it absorbs yellow and orange wavelengths of light
- It allows blue/violet/lilac wavelengths to pass through
- When you look through blue glass at a potassium flame, the yellow is removed and the lilac becomes visible
This is also why sodium contamination is so problematic — even fingerprints on equipment can introduce enough sodium to overwhelm other flame colours. Rigorous cleaning is essential for accurate results.
Limitations of Flame Tests
- Similar colours (calcium vs sodium) can be confused
- Mixtures of metals give mixed, hard-to-interpret colours
- Subjective — colour perception varies between observers
- Not all metals give visible colours
- Cannot quantify — only qualitative identification
Practice questions for Flame Tests
Which type of wire is used to carry out a flame test?
Explain why different metal ions produce different colours in flame tests.