First question : Auto protolysis of water : H
2O + H
2O
H
3O
+ + OH
-Write the equilibrium expression for this equation. Then find the concentration of H
3O
+.
Use pH = -log{[H
3O
+]}
Second question : In this question, not only do you need to consider the dissociation of HCl, but also the dissociation of water (as in the first question), since the concentration of HCl is extremely low. Using both these dissociation equations, find the hydronium ion concentration, and then pH.
Hope this helps