The balanced chemical equation for the reaction between sodium hydroxide and sulfuric acid is:
2NaOH + H2SO4 → Na2SO4 + 2H2O
From the balanced equation, we can see that 2 moles of NaOH react with 1 mole of H2SO4.
The number of moles of NaOH used is:
0.050 L x 0.60 mol/L = 0.030 mol
Since 2 moles of NaOH react with 1 mole of H2SO4, the number of moles of H2SO4 in 20 mL of solution is:
0.030 mol NaOH x (1 mol H2SO4 / 2 mol NaOH) = 0.015 mol H2SO4
The concentration of the sulfuric acid is:
0.015 mol / 0.020 L = 0.75 M