1. CHAPTER 16 Acids and Bases The pH Scale

2. 2 13.2 The pH Scale Soil at a high pH makes hydrangea flowers pink Soil at a low pH makes hydrangea flowers blue

3. 3 13.2 The pH Scale Household chemical Acid or basepH ammoniabase11 bar soapbase10 baking sodabase8.5 soda wateracid4 vinegaracid3 lemon juiceacid2 pH range pH can be less than 0 for stronger acids greater than 14 for stronger bases

4. 4 13.2 The pH Scale p H doesn’t just tell us if a solution is neutral, an acid or a base It also tells us: the concentration of H + ions in the solution in moles/L Water is neutral: [H + ] = 1 x 10 -7 M and pH = 7 pH and [H + ]

5. 5 13.2 The pH Scale p H doesn’t just tell us if a solution is neutral, an acid or a base It also tells us: the concentration of H + ions in the solution in moles/L which is expressed as a p ower of 10 Water is neutral: [H + ] = 1 x 10 -7 M and pH = 7 pH and [H + ]

6. 6 13.2 The pH Scale Power of 10 A negative exponent means the number is less than 1

7. 7 13.2 The pH Scale Definition of pH: pH = –log[H + ] Water is neutral: [H + ] = 1 x 10 -7 M and pH = 7 Do not forget the “–” sign! logarithm: in base 10, a number A derived from another number B such that 10 B =A. The number 7 is the logarithm of 0.000 000 1 pH and [H + ]

8. 8 13.2 The pH Scale [H + ] = 1 MpH = –log(1) = 0 [H + ] = 0.05 MpH = –log(0.05) = 1.3 Examples: Definition of pH: pH = –log[H + ] Water is neutral: [H + ] = 1 x 10 -7 M and pH = 7 The number 7 is the logarithm of 0.000 000 1 pH and [H + ]

9. 9 13.2 The pH Scale [H + ] = 1 MpH = –log(1) = 0[H+] = 10 –pH = 10 –0 = 1 M [H + ] = 0.05 MpH = –log(0.05) = 1.3[H+] = 10 –pH = 10 –1.3 = 0.05 M Examples: Check: Definition of pH: pH = –log[H + ] Water is neutral: [H + ] = 1 x 10 -7 M and pH = 7 The number 7 is the logarithm of 0.000 000 1 pH and [H + ]

10. 10 13.2 The pH Scale A solution of acetic acid (HCH 3 O 2 ) has an H + concentration of 5 x 10 –5 M. What is the pH of the solution? pH and [H + ]

11. 11 13.2 The pH Scale A solution of acetic acid (HCH 3 O 2 ) has an H + concentration of 5 x 10 –5 M. What is the pH of the solution? Asked: pH of a solution Given: [H + ] = 5 x 10 –5 M Relationships:pH = –log[H + ] pH and [H + ]

12. 12 13.2 The pH Scale A solution of acetic acid (HCH 3 O 2 ) has an H + concentration of 5 x 10 –5 M. What is the pH of the solution? Asked: pH of a solution Given: [H + ] = 5 x 10 –5 M Relationships:pH = –log[H + ] Solve: pH = –log[H + ] pH = –log(5 x 10 –5 ) pH = 4.3 Answer: This solution has a pH of 4.3, a relatively weak acid. pH and [H + ]

13. 13 13.2 The pH Scale A solution of nitric acid (HNO 3 ) has a pH of 3. What will the pH be if you add 10 mL of the solution to 90 mL of pure water? pH and [H + ]

14. 14 13.2 The pH Scale A solution of nitric acid (HNO 3 ) has a pH of 3. What will the pH be if you add 10 mL of the solution to 90 mL of pure water? Asked: pH of the new solution Given: old pH = 3 100 mL of the new solution contains 10 mL of the old solution Relationships:A pH value is a power of 10. A change in 1 pH unit means the concentration changes by a factor of 10. pH and [H + ]

15. 15 13.2 The pH Scale A solution of nitric acid (HNO 3 ) has a pH of 3. What will the pH be if you add 10 mL of the solution to 90 mL of pure water? Asked: pH of the new solution Given: old pH = 3 100 mL of the new solution contains 10 mL of the old solution Relationships:A pH value is a power of 10. A change in 1 pH unit means the concentration changes by a factor of 10. Solve:Diluting an acidic solution means the pH increases (fewer H + ) The new pH is 4 (not 2). Answer:The new solution has a pH of 4. pH and [H + ]

16. 16 13.2 The pH Scale Dissociation of water: H 2 O(l) H + (aq) + OH – (aq) [H + ] and [OH – ] are related pH for bases [H + ][OH - ] = 1 x 10 -14 Becomes: pH + pOH = 14

17. 17 13.2 The pH Scale Find the pH of a 0.012 M sodium hydroxide (NaOH) solution. pH for bases

18. 18 13.2 The pH Scale Find the pH of a 0.012 M sodium hydroxide (NaOH) solution. Asked: pH of the solution Given: NaOH is a strong base that dissociates 100% in aqueous solution [OH – ] = 0.012 M Relationships: 14 = pH + pOH pH for bases

19. 19 13.2 The pH Scale Find the pH of a 0.012 M sodium hydroxide (NaOH) solution. Asked: pH of the solution Given: NaOH is a strong base that dissociates 100% in aqueous solution [OH – ] = 0.012 M Relationships: 14 = pH + pOH Solve:pH = 14 – (-log(0.012)) = 14.00 – 1.92 = 12.08 Answer:The solution has a pH of 12.08 and is a strong base. pH for bases

20. 20 13.2 The pH Scale Measuring pH You can’t measure pH by just looking at a solution, or measuring its density or temperature, but you can measure pH indirectly by: - performing a chemical reaction with a solution of known pH

21. 21 13.2 The pH Scale Measuring pH The color of red cabbage juice at different pH You can’t measure pH by just looking at a solution, or measuring its density or temperature, but you can measure pH indirectly by: - performing a chemical reaction with a solution of known pH - using a chemical that changes color at different pH values (pH indicators)

22. 22 13.2 The pH Scale Measuring pH You can’t measure pH by just looking at a solution, or measuring its density or temperature, but you can measure pH indirectly by: - performing a chemical reaction with a solution of known pH - using a chemical that changes color at different pH values (pH indicators)

23. 23 13.2 The pH Scale You can’t measure pH by just looking at a solution, or measuring its density or temperature, but you can measure pH indirectly by: - performing a chemical reaction with a solution of known pH - using a chemical that changes color at different pH values (pH indicators) - measuring the electrical properties of the solution Measuring pH Acids and bases conduct electricity pH and conductivity (flow of electricity) are related a pH meter

24. 24 13.2 The pH Scale pH = –log[H + ] pOH = -log[OH – ] pH = 14 - pOH Finding the pH in acids: Finding the pH in bases: Measuring the pH involves indirect methods Most acids and bases have a pH between 0 and 14

25. 25 13.2 The pH Scale [H + ] = 10 -pH K w = [H + ] [OH – ] [H + ] [OH – ] = 1 x 10 -14 Finding the [H + ] in acids: Finding the [OH - ] in bases: All of the values, pH, pOH, [H + ] and [OH – ] can be calculated using our formulas: