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Chemistry 1011

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). 13.3 pH and pOH. YOU ARE EXPECTED TO BE ABLE TO: Define pH and pOH.

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Chemistry 1011

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  1. 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 5

  2. 13.3 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 5

  3. 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 = -log10 [H+] Chemistry 1011 Slot 5

  4. Logarithms and pH Examples • If a = bc, then logba = c • If a = 10c, then log10a = c • If [H+] = 10-1, then log10 [H+] = -1 or -log10 [H+] = 1 • What is the pH of a solution with a hydrogen ion concentration of 10-2mol/L pH = -log10 [H+] = -log10 [10-2] = 2 Chemistry 1011 Slot 5

  5. pH Examples • What is the pH of a water sample that has a hydrogen ion concentration of 4.0 x 10-5? pH = -log10 [H+] = -log10 [4.0 x 10-5] = • What is the hydrogen ion concentration of a solution with a pH of 5.6? pH = -log10 [H+] 5.6 = -log10 [H+] [H+] = Chemistry 1011 Slot 5

  6. pOH • pOH is determined in the same way as pH pOH = -log10 [OH-] • Since KW = [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 5

  7. 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 [OH-] > 1.0 x 10-7 pH 7 to 14 Chemistry 1011 Slot 5

  8. 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 5

  9. 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, H2SO4(aq)? H2SO4 is a strong acid H2SO4 2H+(aq) + SO42-(aq) [H+] = 2 x 2.5 x 10-2 mol/L pH = -log10 [H+] = -log10 [5.0 x 10-2] = Chemistry 1011 Slot 5

  10. 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 Ba2+(aq) + 2OH-(aq) [OH-] = 2 x 5.0 x 10-2 mol/L pOH = -log10 [OH-] = -log10 [1.0 x 10-1] = 1 pH = 14 - pOH = 13 Chemistry 1011 Slot 5

  11. pH of Common Materials • Lemon Juice 2.2 - 2..4 • Vinegar 3.0 • Tomato Juice 4.0 • Cheese 4.8 - 6.4 • Cow’s Milk 6.3 - 6.6 • Human Saliva 6.5 - 7.5 • Human Blood 7.3 - 7.5 • Seawater 8.3 Chemistry 1011 Slot 5

  12. 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 Chemistry 1011 Slot 5

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