This work analyzes the influence of the pH on the physical-chemical properties of calcium-deficient hydroxyapatite synthesized by the sol-gel method. The pH evolution in the course of the synthesis was followed during the drop-by-drop adding of the calcium source to the phosphorus source, for different drip rates. The structural, morphological, and textural characterizations demonstrate that increasing the drip rate up to values of 10 μl∙s−1 increases the crystallite size and the specific surface area, while the chemical and optical characterizations show that higher drip rates also increase the calcium and oxygen vacancies, related to an increase in the energy of the optical band gap. However, for the sample synthesized at a drip rate of 17 μl∙s−1, the conjunction of higher calcium and oxygen vacancies has an opposite effect in the optical properties, in comparison to the observations in the synthesized samples at lower drip rates. Finally, the thermal characterization shows that, for all cases, the thermal diffusivity values agree with the reported values elsewhere.