When an electric current is passed through a solution containing dilute tetraoxosulphate (Vi) acid, 190 cm3 of…

Analyze the question: A gas is measured at 26°C and 736 mmHg. We need its volume at s.t.p. (273 K, 760 mmHg). This is a combined gas law problem.

Concept: P₁V₁/T₁ = P₂V₂/T₂

Solution:

• P₁ = 736 mmHg, V₁ = 190 cm³, T₁ = 26 + 273 = 299 K
• P₂ = 760 mmHg, T₂ = 273 K, V₂ = ?

V₂ = (P₁ V₁ T₂) / (T₁ P₂)

V₂ = (736 × 190 × 273) / (299 × 760)

Numerator: 736 × 190 = 139,840; 139,840 × 273 = 38,176,320

Denominator: 299 × 760 = 227,240

V₂ = 38,176,320 / 227,240 ≈ 168.0 cm³

Check by simplifying: 190/760 = 0.25, so V₂ = 736 × 0.25 × 273 / 299 = 184 × 273 / 299 = 50,232 / 299 ≈ 168.0 cm³.

Answer: The volume at s.t.p. is about 168 cm³, which is option B.

Tip: At the conditions given, pressure is lower than standard and temperature is higher than standard, so both changes shrink the gas when converting to s.t.p. The answer must be less than 190 cm³. That immediately rules out D and E. Also, 190/760 = 1/4 makes the arithmetic quick.