Explanation:
Example pH Calculations:
(1) What is the pH of (a) human blood, in which the hydronium ion concentration is 4.0 x 10-8 M; (b) 0.020 M HCl(aq); (c) 0.040 M KOH (aq); (d) household ammonia in which the [OH¯]= 3 x 10-3 M; (e) 6.0 x 10-5M HClO4(aq)
Answers: (a) pH = -log(4.0 x 10-8 M ) = 7.4; (b) pH = -log(0.020 M ) = 1.7; (c) pOH = -log(0.040) = 1.4 so pH = 14-1.4 = 12.6; (d) pOH = -log(3 x 10-3 M) = 2.5 so pH = 14-2.5 = 11.5; (e) pH = -log(6.0 x 10-5? M ) = 4.2
(2) Find the hydronium ion concentration in a solution with pH = 4.83
Answer: [H+] = 10-pH = 10-4.83 =1.5 x 10-5 M
(3)The pH of a solution of Ba(OH)2 10.66 at 25ºC. What is the hydroxide ion concentration in the solution? If the solution volume is 125 mL, how many grams of Ba(OH)2 must have been dissolved?
Answer:
14 – 10.66 = 3.34= pOH [OH-] = 10-pOH = 10-3.34 = 4.6 x 10-4 M
1 mole of Ba(OH)2 for every two moles of OH- so 4.6 x 10-4 mol OH x 1 Ba(OH)2/2 OH- = 2.3 x 10-4M Ba(OH)2
0.125 L x 2.3 x 10-4 M Ba(OH)2 = 2.9 x 10-5 moles Ba(OH)2 x 171g/mol = 4.9 x 10-3 g
