25.0 mL of sulfuric acid is neutralised exactly by 20.0 mL of 0.100 M sodium hydroxide. What is the concentration of the acid?
Answer and explanation
Correct answer: B. 0.040 M
- Step 1: Moles NaOH = 0.0200 L x 0.100 M = 0.00200 mol. Step 2. H2SO4 + 2NaOH gives Na2SO4 + 2H2O, so moles acid = 0.00100 mol. Step 3. Concentration = 0.00100 / 0.0250 L = 0.040 M. Answer: 0.040 M. Why not the others: 0.080 M ignores the 1:2 ratio, 0.020 M uses a wrong ratio, and 0.125 M inverts the volumes.
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