pH of solution after adding SiCl4
Silicon is very oxophilic and $\ce{SiCl4}$ irreversibly hydrolyzes in water as follows:
$$\ce{SiCl4_{(l)} + 4 H2O_{(l)} -&gt; 4 HCl_{(aq)} + Si(OH)4_{(s)}} $$

The release of $\ce{HCl}$ creates hydrochloric acid and lowers the pH.