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Hydrogen gives a squeaky pop with a lighted splint. Oxygen relights a glowing splint. Carbon dioxide turns limewater cloudy. Chlorine bleaches damp litmus paper. Give the correct test material and result; observing bubbles proves gas formation but not gas identity. Use laboratory instructions for safe testing and do not smell an unknown gas directly.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Describe gas and ion tests
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Which test identifies carbon dioxide?
Limewater turns cloudy. A calcium carbonate precipitate forms.
After watching 2: What does a flame-emission line pattern help identify?
Metal ions. Different atoms give characteristic emissions.
What you'll be able to do
Hydrogen gives a squeaky pop with a lighted splint. Oxygen relights a glowing splint. Carbon dioxide turns limewater cloudy. Chlorine bleaches damp litmus paper. Give the correct test material and result; observing bubbles proves gas formation but not gas identity. Use laboratory instructions for safe testing and do not smell an unknown gas directly.
Flame tests can identify selected metal ions by characteristic colours. Sodium hydroxide precipitates some metal hydroxides with distinctive colours or behaviour in excess. Carbonate produces carbon dioxide with acid; sulfate forms a white precipitate with suitable acidified barium reagent; halides form silver-halide precipitates after nitric-acid treatment. Separate samples prevent test reagents contaminating later tests. One shared colour may not uniquely identify an ion, so use the full observation pattern.
A pure substance has a characteristic melting point under stated conditions; impurities commonly broaden or depress melting. Chromatography can reveal multiple components, but co-elution limits a purity claim. Flame-emission spectroscopy can detect metal ions sensitively by characteristic spectral lines. Instrumental methods can be rapid and use small samples, though instruments need calibration and reference data. Compare actual evidence rather than assuming every machine result is automatically correct.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Why use a fresh portion for a sulfate test after testing carbonate?
It reduces contamination and ambiguous results.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.