Question

Water gas is produced by

• A. Passing steam over red hot coke
• B. Passing steam and air over red hot coke
• C. Burning coke in excess air
• D. Burning coke in limited supply of air
• E. Both (A) and (B)

Hint:

Remember:
• Water gas = CO + H$_2$ (formed using steam only)
• Producer gas = CO + N$_2$ (formed using air)
• Key difference: presence of nitrogen indicates producer gas

Answer 1

The Correct Option is A

Concept:
Water gas is a mixture of carbon monoxide (CO) and hydrogen (H$_2$). It is an important industrial fuel and also used as a reducing agent. It is produced by passing steam over red hot carbon (coke). The key reaction involved is: \[ \text{C (s)} + \text{H}_2\text{O (g)} \rightarrow \text{CO (g)} + \text{H}_2\text{(g)} \] This is an endothermic reaction, meaning heat must be supplied continuously to maintain the process.

Step 1: Understanding the formation of water gas
When steam is passed over red hot coke (carbon), the above reaction takes place producing a mixture of CO and H$_2$, which is called water gas.

Step 2: Analyze each option
Option (A): Passing steam over red hot coke
This directly corresponds to the reaction: \[ \text{C} + \text{H}_2\text{O} \rightarrow \text{CO} + \text{H}_2 \] Hence, this produces water gas. Correct Option (B): Passing steam and air over red hot coke
This produces producer gas, not water gas. Air introduces nitrogen and oxygen: \[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2, \quad \text{CO}_2 + \text{C} \rightarrow 2\text{CO} \] Resulting gas contains CO, N$_2$, and small H$_2$. Incorrect Option (C): Burning coke in excess air
Produces mainly CO$_2$, not water gas: \[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \] Incorrect Option (D): Burning coke in limited air
Produces CO (producer gas component), but no hydrogen: \[ 2\text{C} + \text{O}_2 \rightarrow 2\text{CO} \] Incorrect Option (E): Both (A) and (B)
Since (B) is incorrect, this option is also incorrect. Final Conclusion:
Only passing steam over red hot coke produces water gas. Hence, the correct answer is: \[ \boxed{(A)} \]