A colourless and odourless gas X burns in oxygen with a pale blue flame. (a) Suggest two gases which X could be. (b) Give one chemical test that could be us...
Question 1 Report
A colourless and odourless gas X burns in oxygen with a pale blue flame.
(a) Suggest two gases which X could be.
(b) Give one chemical test that could be used to confirm which of the two gases X is.
Answer Details
(a) Two possible gases
A colourless, odourless gas that burns in oxygen with a pale blue flame could be hydrogen (H2) or carbon(II) oxide (CO). Both are colourless and odourless, and both burn with a pale blue flame.
(b) Chemical test to distinguish them
Burn a sample of X and test the product of combustion:
- If X is hydrogen, it burns to form water only, which turns white anhydrous copper(II) tetraoxosulphate(VI) blue (or blue cobalt chloride paper pink) and gives no reaction with limewater.
- If X is carbon(II) oxide, it burns to form carbon(IV) oxide, which turns limewater milky. \[2CO + O_2 \rightarrow 2CO_2\]
Therefore, passing the combustion product into limewater identifies the gas: a milky precipitate confirms carbon(II) oxide, while the formation of water confirms hydrogen.
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