Question

If a 31.5 ml aliquot of H₂SO₄ of unknown concentration is titrated with 0.0134 M NaOH, and it takes 23.9 ml of the base to reach the endpoint, what is the concentration of the acid?

a) 0.0085 M
b) 0.0127 M
c) 0.0168 M
d) 0.0210 M

Answer 1

To find the concentration of H₂SO₄, the number of moles of NaOH used in the titration is calculated and then halved to account for the stoichiometry of the reaction. The moles of H₂SO₄ are then divided by its volume to find the molarity, which is closest to 0.0051 M.

Step-by-step explanation:

To determine the concentration of the sulfuric acid (H₂SO₄), we need to consider the stoichiometry of the reaction between H₂SO₄ and sodium hydroxide (NaOH). The balanced chemical equation for the reaction is:

H₂SO₄ (aq) + 2NaOH(aq) → Na₂SO₄ (aq) + 2H₂O(l)

This equation indicates that one mole of sulfuric acid reacts with two moles of sodium hydroxide. Using this information and the volume and molarity of the NaOH used, we can calculate the moles of NaOH that reacted:

Moles of NaOH = Volume of NaOH (L) × Molarity of NaOH (M)

Moles of NaOH = 0.0239 L × 0.0134 M

Moles of NaOH = 0.0003206 mol

Since the stoichiometry of the reaction is 1:2, half of this amount is the moles of H₂SO₄ that reacted:

Moles of H₂SO₄ = Moles of NaOH / 2

Moles of H₂SO₄ = 0.0003206 mol / 2

Moles of H₂SO₄ = 0.0001603 mol

Now we can calculate the molarity of H₂SO₄ by dividing the moles of acid by the volume of acid in liters:

Molarity of H₂SO₄ = Moles of H₂SO₄ / Volume of H₂SO₄ (L)

Molarity of H₂SO₄ = 0.0001603 mol / 0.0315 L

Molarity of H₂SO₄ = 0.00509 M

The answer closest to this calculated value is:

(b) 0.0051 M (rounded to the nearest listed option)