A student titrated a solution of 25 cm3 of NaOH of concentration 0.1 mol/dm3 with H2SO4. She achieved four results; 25.8 cm3, 26.15 cm3, 26.25 cm3 and 26.45 cm3. Calculate the concentration of H2SO4 using concordant titres.

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
Concordant titres: 26.15 cm³ and 26.25 cm³
Mean titre: (26.15+26.25)/2= 26.2 cm³/1000= 0.0262 dm³
moles of NaOH: (25/1000)*0.1= 0.0025 mol
Ratio of H₂SO₄: NaOH= 1:2
Moles of H₂SO₄: 0.0025/2= 0.00125 mol
Concentration of H₂SO₄: 0.00125/0.0262= 0.0477 mol dm^-3