Question

How many grams of pure NaOH must be used to prepare 10.0 L of a solution that has a pH of 13?

Answer 1

First step is to determine the concentration to do this you use the formula
pH=-log[H+]
13=-log[H+]
10^-13=[H+]
That'll give you the concentration of H+ ions

Answer 2

Now you have to find the mass of NaOH to do this you have to use the formula
m=cv
m is mass which is your unknown
c is the concentration which you found in the previous step
v is the volume which is the 10L