The molar concentration of the potassium hydroxide solution was 0.815 mol/L.
Balanced equation: 2KOH + H_2SO_4 → K_2SO_4 + 2H_2O
Moles of H_2SO_4:
15.1 mL H_2SO_4 × (1.50 mmol H_2SO_4 /1 mL H_2SO_4)
= 22.65 mmol H_2SO_4
Moles of KOH: 22.65 mmol H_2SO_4× (2 mmol KOH/2 mmol H_2SO_4)
= 45.30 mmol KOH
Concentration of KOH: c= "moles"/"litres" = 45.30 mmol/55.6 mL
= 0.815 mol/L