Generated by claude-sonnet-4-6 · 2026-06-15 06:47 · grounding rag
Model Answer
(i) Two metals that react violently with cold water: Sodium (Na) and Potassium (K).
Observations:
- The metal melts and moves rapidly on the surface of water.
- A hissing sound is produced and the metal may catch fire (potassium burns with a lilac flame).
- The water turns pink/red when a few drops of phenolphthalein indicator are added, showing the solution formed is alkaline (metal hydroxide is produced).
(ii) Test for hydrogen gas: Bring a burning candle/matchstick near the mouth of the inverted test tube collecting the gas. If the gas burns with a 'pop' sound, it confirms the gas is hydrogen.
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Explanation
- For (i), the question asks for two metals + three observations — both marks depend on getting all five points. Common metals chosen are Na and K. Observations must be distinct: physical behaviour, sound/flame, and alkaline nature of solution.
- For (ii), the standard test for H₂ is the pop test — always mention the burning splint and the characteristic pop sound. This is a 1-mark point so one clear sentence is enough.
- These metals react as: $2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2\uparrow$ — knowing the equation helps justify observations.