Magnetite nanoparticles with particle size ~ 10 and 16 nm are synthesized by varying pH of the initial solution during chemical co-precipitation method. The X-ray diffraction patterns confirm the formation of spinel phase; however, the Raman spectra show an impure phase of antiferromagnetic Fe2O3 in the sample of smaller nanoparticles (10 nm). The cation distribution of these nanoparticles is estimated using the lattice parameter. Lower saturation magnetization of these samples, as compared to bulk, has been attributed to larger surface area of these samples. Same aspect has also been investigated from the optical band gap variation of these nanoparticles. Almost one third value of magnetization of smaller nanoparticles compared to larger one is due to the presence of Fe2O3 phase. The motive of the present study is to correlate the properties of magnetite nanoparticles with the synthesis parameters like pH and hence to tune them according to particular applications.