Question

A carbon compound 'P' on heating with excess conc. H2SO4 forms another carbon compound 'Q' which on addition of hydrogen in the presence of nickel catalyst forms a saturated carbon compound 'R'. One molecule of 'R' on combustion forms two molecules of carbon dioxide and three molecules of water. Identify P, Q, R and write chemical equations for the reactions involved.

Answer 1

Compound 'P' is ethanol (C2H5OH), which dehydrates to form ethene ('Q', C2H4). Ethene is hydrogenated to form ethane ('R', C2H6), and the complete combustion of ethane produces two molecules of carbon dioxide and three molecules of water.

Step-by-step explanation:

The question relates to the identification of organic compounds and their reactions involved in converting one compound to another, particularly through dehydration and hydrogenation processes. Given that the final combustion product of the saturated compound ('R') yields two molecules of carbon dioxide and three molecules of water, we can deduce that 'R' has two carbon atoms and likely three hydrogen atoms on each carbon.

Working backwards, 'Q' would be the alkene with two carbon atoms since its hydrogenation yields 'R', the saturated hydrocarbon. 'P,' being the precursor to 'Q', must then be an alcohol since its dehydration with concentrated sulfuric acid produces the alkene 'Q'.

The alcohol 'P' is likely ethanol (C2H5OH), which dehydrates to ethene (C2H4) 'Q'. Hydrogenation of ethene with a nickel catalyst produces ethane (C2H6) 'R'. The reaction equations are:

• Dehydration of ethanol: C2H5OH (l) → C2H4 (g) + H2O (l)
• Hydrogenation of ethene: C2H4 (g) + H2 (g) → C2H6 (g)
• Combustion of ethane: C2H6 (g) + 7/2 O2 (g) → 2 CO2 (g) + 3 H2O (g)