Calculate the mass of LiOH that must be added to 200mL of a 0.100 M solution of HCl to bring the pH to 2.00.?

Answer 1

The concentration of the original solution is 0.100 M or 0.100mol/L. To reduce the pH of the solution to 2.00, the H+ concentration should be 0.01mol/L (remember: pH = -log H+). This means you need to neutralize 0.09 mol H+ with 0.09mol OH- from that will be coming from the LiOH. To simplify the solution, let us first assume a L solution.

Computing for the weight of LiOH equivalent to 0.09 mmol:
mass = 23.95g/mol x 0.09mol = 2.1555 g

But remember this amount is needed for every L of solution. Since you only have 200mL, you need to multiply the result w/ 0.200L to give you the mass of LiOH that will neutralize only 200mL of acid. The answer is 431.1 mg (or 0.431 g)