Question

Question 1 a chemist dissolves 154.mg of pure hydrochloric acid in enough water to make up 170.ml of solution. calculate the ph of the solution. be sure your answer has the correct number of significant digits

Answer 1

HCl is a strong acid and completely dissociates to give out H⁺ ions
Therefore [HCl] = [H⁺] 
number of HCl moles - 154 x 10⁻³ g/ 36.5 g/mol = 4.22 mmol 
[HCl] = 4.22 x 10⁻³ mol / 0.170 L = 0.025 M
therefore [H⁺] = 0.025 M
by knowing the H⁺ concentration, pH can be calculated
pH = -log[H⁺]
pH = -log (0.025 M)
pH = 1.60