Sodium reacts with water to give hydrogen gas and sodium hydroxide solution - HSC - SSCE Chemistry - Question 14 - 2013 - Paper 1

From the balanced chemical equation for the reaction of sodium with water:

$2\,Na + 2\,H_2O \rightarrow 2\,NaOH + H_2$

According to the equation, 2 moles of sodium produce 1 mole of hydrogen gas. Therefore, 1 mole of sodium will produce:

$\frac{1}{2} \cdot 1\,mol = 0.5\,mol \, H_2$

Using the Ideal Gas Law, which states:

$PV = nRT$

Where:

• P is pressure (100 kPa = 100,000 Pa)
• V is volume (in m³)
• n is the number of moles (0.5 mol)
• R is the gas constant (8.314 J/(mol·K))
• T is temperature (25°C = 298 K)

Rearranging for V gives:

$V = \frac{nRT}{P} = \frac{0.5\,mol \cdot 8.314\,J/(mol\cdot K) \cdot 298\,K}{100,000\,Pa}$

Calculating this:

$V = \frac{0.5 \cdot 8.314 \cdot 298}{100,000} \approx 0.0124\,m^3$

Converting to liters (1 m³ = 1000 L):

$V \approx 12.40\,L$

The calculated volume of hydrogen gas produced from the reaction is approximately 12.40 L, thus the answer is (B) 12.40 L.