pH Worksheet Solutions Note: The significant figures in the concentration of [H+] or [OH -] is equal to the number of decimal places in the pH or pOH and vice versa. 1) Find the pH of a solution that contains 85 grams of hydrochloric acid (HCl) dissolved in 2.5 L of water. 85 g HCl x 1 mole HCl = 2.3 mole HCl 36.5 g HCl 2.3 mole HCl = 0.92 M HCl 2.5 L H2O pH = - log (0.92) = 0.03 2) Find the pH of a solution that contains 2.95 grams of nitrous acid (HNO2) dissolved in 550 mL of water. 2.95 g HNO2 x 1 mole HNO2 = 0.0628 mole HNO2 47 g HNO2 0.0628 mole HNO2 = 0.11 M HNO2 0.55 L H2O pH = - log (0.11) = 0.96 3) Find the pH of a solution that contains 2.5 moles of hydrochloric acid (HCl) and 1.4 moles of acetic acid (HC2H3O2) dissolved in 110 L of water. 2.5 mole HCl + 1.4 mole HC2H3O2 = 3.9 mole acid 3.9 mole acid = 0.035 M solution 110 L H2O pH = -log (0.035) = 1.46 4) A solution has a [H+] concentration of 5.3 x 10-6 M. Is this an acidic or basic solution? Why? pH = -log (5.3 x 10-6) = 5.28 This solution is slightly acidic because its pH < 7. 5) If an acidic solution having a pH of 3.95 is diluted from 15 mL to a final volume of 100. mL, what would be the pH of the resulting solution? 3.95 = -log x 3.95 = log x-1 3.95 log x-1 10 = 10 8912.5 = x-1 x= 1 = 1.1 x 10-4 M 8912.5 M1V1 = M2V2 M2 = M1V1 = (1.1 x 10-4 M)(15 mL) = 1.7 x 10-5 M V2 (100. mL) pH = -log (1.7 x 10-5) = 4.77