Why is concentrated H2SO4 not used to prepare hydrogen in the laboratory?
AIt does not react with zinc at all
BIt freezes solid below ten degrees Celsius
CIt is cheaper than the dilute acid form
DIt oxidises hydrogen back to water vapour
Answer & Solution
Correct answer: D. It oxidises hydrogen back to water vapour
1. Concentrated H2SO4 is a strong oxidising acid.
2. It oxidises the hydrogen formed back to water.
3. It also gives SO2 instead, not H2.
4. So dilute H2SO4 is preferred.
_Source: Selina Concise Chemistry Class 8, Ch on Hydrogen (Mistral OCR'd PDF), section on lab preparation precautions_
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