Chemistry 1011 Slot 51 Chemistry 1011 TOPIC Acids and Bases TEXT REFERENCE Masterton and Hurley Chapter 4.2 (Review), 13, 14.1, 15.1 (page 427), 21.2 (page589)

Chemistry 1011 Slot pH and pOH YOU ARE EXPECTED TO BE ABLE TO: Define pH and pOH. Calculate the pH and pOH of a solution given the concentration of hydrogen ions or the concentration of hydroxide ions, and vice versa. Identify strong acids and bases Calculate the pH and pOH of solutions of strong acids and bases of known concentration. Identify methods of measuring pH

Chemistry 1011 Slot 53 Defining pH The acidity or basicity of a solution can be described by the [H + ] or [OH  ] These concentrations can vary from 10  1 to 10  14 The pH scale was proposed in order to provide an easier means of describing acidity pH =  log 10 [H + ]

Chemistry 1011 Slot 54 Logarithms and pH Examples If a = b c, then log b a = c If a = 10 c, then log 10 a = c If [H + ] = 10  1, then log 10 [H + ] =  1 or  log 10 [H + ] = 1 What is the pH of a solution with a hydrogen ion concentration of 10  2 mol/L pH =  log 10 [H + ] =  log 10 [10  2 ] = 2

Chemistry 1011 Slot 55 pH Examples What is the pH of a water sample that has a hydrogen ion concentration of 4.0 x 10  5 ? pH =  log 10 [H + ] =  log 10 [4.0 x 10  5 ] = What is the hydrogen ion concentration of a solution with a pH of 5.6? pH =  log 10 [H + ] 5.6 =  log 10 [H + ] [H + ] =

Chemistry 1011 Slot 56 pOH pOH is determined in the same way as pH pOH =  log 10 [OH  ] Since K W = [H + ] x [OH  ] = 1.0 x 10  14 It follows that pH + pOH = 14 If a solution has a pH of 5.6, then the pOH will be 8.4 It will be basic

Chemistry 1011 Slot 57 Interpreting the pH Scale In an acidic solution, [H + ] > 1.0 x 10  7 [OH  ] < 1.0 x 10  7 pH 0 to 7 In a basic solution, [H + ] 1.0 x 10  7 pH 7 to 14

Chemistry 1011 Slot 58 Calculating the pH of a Strong Acid Strong acids and bases are fully ionized in dilute aqueous solution HCl (aq) H + (aq) + Cl  (aq) NaOH (aq) Na + (aq) + OH  (aq) The [H + ] or [OH  ] can be determined from the [acid] or [base]

Chemistry 1011 Slot 59 Example - Calculating the pH of a Strong Acid What is the pH of a 2.5 x 10  2 mol/L solution of sulfuric acid, H 2 SO 4(aq) ? H 2 SO 4 is a strong acid H 2 SO 4 2H + (aq) + SO 4 2  (aq) [H + ] = 2 x 2.5 x 10  2 mol/L pH =  log 10 [H + ] =  log 10 [5.0 x 10  2 ] =

Chemistry 1011 Slot 510 Example - Calculating the pH of a Strong Base What is the pH of a 5.0 x 10  2 mol/L solution of barium hydroxide, Ba(OH) 2(aq) ? Ba(OH) 2 is a strong base Ba(OH) 2 Ba 2+ (aq) + 2OH  (aq) [OH  ] = 2 x 5.0 x 10  2 mol/L pOH =  log 10 [OH  ] =  log 10 [1.0 x 10  1 ] = 1 pH = 14  pOH = 13

Chemistry 1011 Slot 511 pH of Common Materials Lemon Juice Vinegar3.0 Tomato Juice4.0 Cheese Cow’s Milk Human Saliva Human Blood Seawater8.3

Chemistry 1011 Slot 512 Measuring pH pH Meter Acid-base indicators –fruit juices –litmus –universal indicator (a mixture of different indicators that change colour at different pH’s) –indicator paper