Question

A solution of H2SO4 is titrated against 1.2 M KOH. It takes 345.0 mL of KOH before the 500 mL sample of H2SO4 reaches an endpoint (the universal indicator changes color). What is the concentration of the H2SO4?

Answer 1

concentration of sulphuric acid is 3.478 mol/L

Step-by-step explanation:

The sulphuric acid (H₂SO₄) is the solution in the flask. We know this from "500 mL sample of H₂SO₄". The solution in the flask is a fixed, quantitatively measured sample (or aliquot).

The potassium hydroxide (KOH) is a primary standard base solution, with concentration 1.2 mol/L. Thus, the KOH is the solution (titrant) in the burette.

To calculate the concentration (c) of H₂SO₄, we require moles (n) and volume (V).

Since in a chemical reaction, the reactants and products remain in stoichiometric ratios, we can find the number of moles of KOH used.

H₂SO₄(aq) + 2KOH(aq) → K₂SO₄(aq) + 2H₂O(l)

The ratio of H₂SO₄ to KOH is therefore, 1 : 2, and therefore,

number of moles of H₂SO₄ = 1/2 × number of moles of KOH

Number of moles can be calculated by multiplying concentration in mol/L by volume in L

n(KOH) = cV = 1.2(from the question) / 0.3450 (titre of KOH used)

= 3.47826 mol

n(H₂SO₄) = 1/2 n(KOH) = 1.73913 mol

now we have moles, as well as volume (500 mL sample), we can calculate concentration by rearranging the formula used to find moles.

c(H₂SO₄) = n/V = 1.73913 / 0.500 = 3.478 mol/L