in your question formulation, you have forgotten to take into account $\ce{H2O2}$ is a weak acid. The title should rather be: **Neutralisation between calcium hydroxide and 30% hydrogen peroxide"** Unless $\ce{Ca(OH)2}$ is in excess over a weak acid as $\ce{H2O2}$ - and it was said it was not - $\mathrm{pH}$ would be always lower than pH of the hydroxide. $$\mathrm{pH}=\mathrm{p}K_ \mathrm{a} + \log \frac{[\ce{HO2-}]}{[\ce{H2O2}]}$$ The hydroxide forms from $\ce{H2O2}$ the $\mathrm{pH}$ buffer solution of a weak acid and it's salt. $$\ce{H2O2 <<=> H+ + HO2-}$$ $$\ce{H+ + OH- <=>> H2O}$$ Additionally, if $\ce{HO2-}$ is partially eliminated by precipitation, the ratio $ \frac{[\ce{HO2-}]}{[\ce{H2O2}]}$ is kept low and so does $\mathrm{pH}$. $$\ce{CaOH+ + HO2- + 7 H2O <=>> CaO2 \cdot 8 H2O}$$ $\ce{Ca(OH)2}$: $\mathrm{p}K_\mathrm{b2} =2.43$ ( Wikipedia ) Note also the hydrogen peroxide is weakly acidic even without addition of sulphuric acid and that it's $ \mathrm{p}K_ \mathrm{a}$ depends on $\ce{H2O2}$ concentration. [H2O2 pH-and-Ionization-Constant][1] [The solubility constant of calcium peroxide octahydrate in relation to temperature; its influence on radiolysis in cement-based materials][2] [1]: http://www.h2o2.com/technical-library/physical-chemical-properties/thermodynamic-properties/default.aspx?pid=51&name=pH-and-Ionization-Constant [2]: https://www.sciencedirect.com/science/article/pii/S0022311511008440