Question

If 40.27 mL of 0.100 M NaOH is required to neutralize 0.314 g of an unknown monoprotic acid, what is the molecular weight of this unknown acid?

Answer 1

first you write the equation:
NaOH + HX -> NaX + H2O

now lets start with basics:

n=m/M
c=n/V

so

n(NaOH) = c(NaOH)*V(NaOH)
n(NaOH) = 40,27 * 10^-3 dm3 * 0,1 mol dm^3
n(NaOH) = ??? mol

n(HX) / n(NaOH) = 1/1 =1

so

n(HX)=n(NaOH)

M(HX) = m(HX) / n(HX)
M(HX) = 0,314 g / ???? mol