A student titrates a \(25.0 \text{ mL}\) sample of \(0.10 \text{ M HA(aq)}\) (a weak monoprotic acid) with \(0.10 \text{ M NaOH(aq)}\). At a point during the titration before the equivalence point is reached, the \(\text{pH}\) of the mixture is measured to be \(\text{pH} = \text{p}K_a - 1.00\), where \(\text{p}K_a\) is the negative logarithm of the acid dissociation constant of \(\text{HA}\). What fraction of the initial amount of \(\text{HA}\) remains unreacted in the solution at this point?