If it takes 50.0 ml of 0.5 m ca(oh)2 solution to completely neutralize 125 ml of hno solution, what is the concentration of the hno3 solution?

the balanced equation for the reaction is

Ca(OH)₂ + 2HNO₃ ---> Ca(NO₃)₂ + 2H₂O

Molar ratio of Ca(OH)₂ to HNO₃ is 1:2

Number of moles of Ca(OH)₂ reacted - 0.5 moldm⁻³ x 50.0 x 10⁻³ dm³

number of Ca(OH)₂ moles  - 0.025 mol

according to the molar ratio

1 mol of Ca(OH)₂ reacts with 2 mol of HNO₃

therefore 0.025 mol of Ca(OH)₂ reacts with - 2 x 0.025 = 0.05 mol of HNO₃

there are 0.05 mol of HNO₃ in 125 mL

and concentration = number of moles / volume in 1 dm³

concentration = 0.05 mol / 125 x 10⁻³ dm

concentration of HNO₃ = 0.4 mol/dm³