Calculate the molarity of an unknown sulfuric acid (H₂SO₄) solution if a 25.0 mL sample of the acid solution consumes 27.2 mL of 0.138 M NaOH solution in a titration. Assume the reaction is: H₂SO₄ + 2 NaOH → Na₂SO₄ + 2 H₂O.

• A. 0.138 M
• B. 0.069 M
• C. 0.0756 M
• D. 0.150 M

Answer: (C)

Verified step by step guidance

1. Start by writing the balanced chemical equation for the reaction: ${H2}_{\mathrm{SO}4}+2{\mathrm{NaOH}}_{}\to {\mathrm{Na}2}_{\mathrm{SO}4}+2{H2}_O$. This shows that one mole of ${H2}_{\mathrm{SO}4}$ reacts with two moles of ${\mathrm{NaOH}}_{}$.
2. Calculate the moles of ${\mathrm{NaOH}}_{}$ used in the titration. Use the formula: $\mathrm{moles}=\mathrm{molarity}\times \mathrm{volume}$. Convert the volume from mL to L by dividing by 1000: $27.2\times 0.138\times 0.001$.
3. Determine the moles of ${H2}_{\mathrm{SO}4}$ that reacted. Since the balanced equation shows a 1:2 ratio between ${H2}_{\mathrm{SO}4}$ and ${\mathrm{NaOH}}_{}$, divide the moles of ${\mathrm{NaOH}}_{}$ by 2.
4. Calculate the molarity of the ${H2}_{\mathrm{SO}4}$ solution using the formula: $\mathrm{molarity}=\frac{\mathrm{moles}}{\mathrm{volume}}$. Use the moles calculated in the previous step and the volume of the ${H2}_{\mathrm{SO}4}$ solution in liters (25.0 mL converted to 0.025 L).
5. Review the calculation steps to ensure accuracy and consistency with the balanced chemical equation and the stoichiometry involved. This will help verify the molarity of the sulfuric acid solution.