A fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 gm carbon dioxide, 0.69 gm of water and no other products. A volume of 10 lit (measured at STP) of this gas is found to weigh 11.6 gm.<br>(a) Calculate (i) empirical formula (ii) molecular mass of the gas (iii) molecular formula<br>(b) Write one single step preparation of the gas<br>(c) Does it react with bromine? If so what colour change do you expect?<br>(d) What do you expect the calorific value of the gas with reference to marsh gas?

PLACEHOLDER ANSWER - the question has several parts. (a) Carbon is $$\frac{3.38}{44} \approx 0.0768$$ mol and hydrogen is $$\frac{2 \times 0.69}{18} \approx 0.0767$$ mol, a ratio of $$1 \colon 1$$, so the empirical formula is CH; the molar mass is $$\frac{11.6 \times 22.4}{10} \approx 26$$, so the molecular formula is $$\text{C}_2\text{H}_2$$ (acetylene). (b) $$\text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{C}_2\text{H}_2$$. (c) Yes, it adds bromine, so the reddish-brown colour of bromine water disappears. (d) Per mole, acetylene gives more heat than marsh gas (methane), about 1300 kJ against 890 kJ, and it burns with a much hotter flame, although per gram its calorific value is slightly lower.