Question

what mass of H 2 O is needed to completely react with 5.10g SiCl4

Answer 1

SiCl4 + 2 H2O → SiO2 + 4 HCl

The ratio r of mass of H2O to SiCl4 is therefore
r = 2*(molar mass of water)/(molar mass of SiCl4)