pH Worksheet 2 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 9.8 x 10-4 M HI solution. pH = -log (9.8 x 10-4) = 3.01 2) Find the pH of a 2.76 x 10-4 M NaOH solution. pOH = -log (2.76 x 10-4) = 3.559 pH = 14.000 – 3.559 = 10.441 3) Find the pH of a solution made by diluting 35 mL of 4.5 M HNO3 to a final volume of 2.25 L. M1V1 = M2V2 M2 = M1V1 = (4.5 M)(35 mL) = 0.070 M V2 (2250 mL) pH = -log (0.070) = 1.15 4) Find the pH of 4.75 L of an aqueous solution that contains 3.20 grams of HCl and 1.85 grams of nitrous acid. 3.20 g HCl x 1 mole HCl = 0.0878 mole HCl 36.45 g HCl 1.85 g HNO2 x 1 mole HNO2 = 0.0394 mole HNO2 47 g HNO2 0.0878 mole HCl + 0.0394 mole HNO2 = 0.1272 moles acid 0.1272 moles acid = 0.0268 M acid solution 4.75 L H2O pH = -log (0.0268) = 1.572 5) Find the pOHs for the solutions in problems 1 – 4 above: #1) pOH = 14.00 – 3.01 = 10.99 #2) pOH = 3.559 #3) pOH = 14.00 – 1.15 = 12.85 #4) pOH = 14.000 – 1.572 = 12.428