You are given 5.00 mL of an H₂SO₄ solution of unknown concentration.You divide the 5.00-mL sample into five 1.00-mL samples and titrate each separately with 0.1000 M NaOH.In each titration the H₂SO₄ is completely neutralized.The average volume of NaOH solution used to reach the endpoint is 15.6 mL.What was the concentration of H₂SO₄ in the 5.00-mL sample?

Question

Quizplus · Accepted Answer

Since the average volume of NaOH used to reach the endpoint in each titration is 15.6 mL and the NaOH concentration is 0.1000 M, the number of moles of NaOH used in each titration is (0.1000 M) x (15.6 mL) = 0.00156 mol. In each titration, this amount of NaOH reacts with the amount of H₂SO₄ originally present in the 1.00-mL sample. Thus, the concentration of H₂SO₄ in the 1.00-mL sample is 0.00156 mol / 1.00 mL = 0.00156 M. To find the concentration in the 5.00-mL sample, we can use the fact that moles of solute is conserved between the 1.00-mL and 5.00-mL samples: (0.00156 M) x (1.00 mL) = (concentration in 5.00 mL) x (5.00 mL) Solving for the concentration in the 5.00-mL sample gives a value of 0.00780 M, which is answer choice C.

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