Water gas is a mixture of:
- (a)CO₂ and H₂
- (b)CO and H₂
- (c)CO₂ and H₂O
- (d)CO and H₂O
Correct — B, CO and H₂. Water gas is made by blowing steam over a bed of white-hot coke (carbon): C + H₂O → CO + H₂. The product is therefore a mixture of carbon monoxide and hydrogen, roughly in equal proportions. Both are combustible, which is why water gas burns with a hot flame and was once used as an industrial fuel and as a feedstock (synthesis gas) for making other chemicals.
- (a)CO₂ and H₂ — Carbon dioxide (CO₂) does not burn, so a fuel gas would not be built around it. In water gas the carbon is only partially oxidised to carbon monoxide, not fully to carbon dioxide.
- (c)CO₂ and H₂O — Both carbon dioxide and water vapour are products of complete combustion and neither is a fuel. A mixture of the two would not burn at all, so it cannot be water gas.
- (d)CO and H₂O — The steam (H₂O) is the raw material passed over the coke; it is consumed in the reaction and reappears as hydrogen, not as unreacted water. Water gas is CO plus H₂, not CO plus H₂O.
Water gas is a manufactured fuel gas produced by the reaction of steam with red-hot carbon (coke). The reaction C + H₂O → CO + H₂ is endothermic, so the coke bed cools and must be periodically reheated with a blast of air. The resulting gas is an equimolar mixture of carbon monoxide and hydrogen.
The way to reason to the answer is to remember that a fuel gas must contain combustible components. Carbon monoxide and hydrogen both burn; carbon dioxide and water vapour do not. That immediately rules out any option containing CO₂ or leaving H₂O unreacted, leaving only carbon monoxide plus hydrogen. It also helps to contrast water gas with producer gas, made by passing limited air over coke, which is mainly carbon monoxide diluted with nitrogen.
- Water gas is a mixture of carbon monoxide and hydrogen, made by passing steam over white-hot coke.
- The forming reaction is C + H₂O → CO + H₂ and is endothermic, so the fuel bed needs reheating.
- A carbon-monoxide-plus-hydrogen mixture is also called synthesis gas (syngas), a feedstock for many chemicals.
- Producer gas, by contrast, is carbon monoxide mixed with nitrogen, made by passing limited air over hot coke.
Water gas is the carbon-monoxide-and-hydrogen mixture; note how it differs from producer gas (CO diluted by nitrogen).
- Confusing water gas (CO + H₂) with producer gas (CO + N₂).
- Thinking the steam stays as water vapour in the product, rather than being converted to hydrogen.
Asked as a direct 'water gas is a mixture of' question or as a match-the-list pairing fuel gases with their constituents.
Match List I (Fuel Gases) with List II (Major Constituents): (A) CNG (B) Coal gas (C) LPG (D) Water gas; 1. Carbon monoxide, Hydrogen 2. Butane, Propane 3. Methane, Ethane 4. Hydrogen, Methane, Carbon monoxide
- (a) A 2 B 1 C 3 D 4
- (b) A 3 B 4 C 2 D 1
- (c) A 2 B 4 C 3 D 1
- (d) A 3 B 1 C 2 D 4
Answer(b) A-3, B-4, C-2, D-1
Same concept and it directly corroborates the NDA answer — its key matches Water gas (D) to constituent 1, 'Carbon monoxide, Hydrogen'. The match-list also contrasts water gas with coal gas (hydrogen, methane and carbon monoxide) and CNG (methane, ethane), reinforcing the fuel-gas distinctions.
- practice — not a real PYQ
Producer gas is chiefly a mixture of:
- (a)Carbon monoxide and nitrogen
- (b)Carbon dioxide and hydrogen
- (c)Methane and ethane
- (d)Hydrogen and oxygen
Answer(a) Carbon monoxide and nitrogen — made by passing limited air over red-hot coke.
- practice — not a real PYQ
Passing steam over red-hot coke to make water gas produces which gases?
- (a)CO₂ and H₂O
- (b)CO and H₂
- (c)CH₄ and CO₂
- (d)N₂ and H₂
Answer(b) CO and H₂ — the reaction is C + H₂O → CO + H₂.