1. Chapter 16 pH and Titration

2. I. Concentration Units for Acids and Bases A. Chemical Equivalents A. Chemical Equivalents 1. Definition: The number of acidic H + or the number of OH - 1. Definition: The number of acidic H + or the number of OH - a. Acid: mass of one equivalent is numerically equal to the mass of one mole of the acid divided by the number of protons( H 3 O + ) that one mole of the acid can provide a. Acid: mass of one equivalent is numerically equal to the mass of one mole of the acid divided by the number of protons( H 3 O + ) that one mole of the acid can provide Example: Example: HCl 36 g/mol; 1 eq = 1 H 3 O + ; 36 g/mol H 3 O + HCl 36 g/mol; 1 eq = 1 H 3 O + ; 36 g/mol H 3 O + H 2 SO 4 98g/mol; 2 eq = 2 H 3 O + ; 49 g/mol H 3 O + H 2 SO 4 98g/mol; 2 eq = 2 H 3 O + ; 49 g/mol H 3 O +

3.  b. Base: mass of one equivalent is numerically equal to the mass of one mole of the base divided by the number of hydroxide (OH - ) that one mole of the base can provide  Example: NaOH 40 g/mol; 1 eq = 1 OH - ; 40 g/mol OH - NaOH 40 g/mol; 1 eq = 1 OH - ; 40 g/mol OH - Ca(OH) 2 74 g/mol; 2 eq = 2 OH - ; 37 g/mol OH - Ca(OH) 2 74 g/mol; 2 eq = 2 OH - ; 37 g/mol OH -

4. B. Normality Definition: number of equivalents of solute per liter of solution Definition: number of equivalents of solute per liter of solution N = eq of solute N = eq of solute L of solution L of solution

5. C. Relationship Between Normality and Molarity N = nM N = nM N: Normality N: Normality n: number of equivalents (# of H + = or OH - ) n: number of equivalents (# of H + = or OH - ) M: Molarity M: Molarity Example: Example: 1M HCl = 1N HCl 1M NaOH = 1N NaOH 1M HCl = 1N HCl 1M NaOH = 1N NaOH 1M H 2 SO 4 = 2N H 2 SO 4 1M Ca(OH) 2 = 2N Ca(OH) 2 1M H 2 SO 4 = 2N H 2 SO 4 1M Ca(OH) 2 = 2N Ca(OH) 2

7. II. Aqueous Solutions and the Concept of pH A. Self-Ionization of Water 1. Definition: Two water molecules interact to produce a hydronium ion and a hydroxide ion by proton transfer - forms a weak electrolyte 2. [ ] is symbol used to indicate concentration in moles per liter (Molarity)

8. 3. H 2 O + H 2 O H 3 O + + OH - ; in pure water [H 3 O + ] = [OH - ]

10. 4. [H 3 O + ][OH - ] = 1 x 10 -14 5. If the [H 3 O + ] increases then the [OH - ] decreases or If the [H 3 O + ] decreases then the [OH - ] increases

11. pH scale

13. B. The pH scale 1. pH -- the negative of the common logarithm of the hydronium ion concentration pH = -log [H 3 O + ] 2. Acid: pH < 7 3. Base: pH > 7 4. Neutral: pH = 7

14. Measurements with pH 1.Indicators (more on this later) 2.pH probes

15. pH paper

16. C. Calculations involving pH Calculate the pH of a 0.001 M HCl

17. Example: 1. Determine the hydronium concentration, and hydroxide concentration of a solution that has a pH of 7.52.

18. 2.3 x 10 -5 M HBr Determine the [OH - ] = pH = pOH =

19. Calculate the pH of a 3.6 X 10 -2 M solution of lithium hydroxide.

20. III. Acid-Base Titrations A. Indicators 1. Definitions: a. indicators - weak acid or base dyes whose colors are sensitive to pH b. transition interval - the pH range over which an indicator changes color

21. 2. Types of indicators a. Change color at about pH 7 b. Change color below pH 7 c. Change color above pH 7

24. B. The Principle of Titration Definitions: 1. Titration - the controlled addition and measurement of the amount of a solution of known concentration with a measured amount of a solution of unknown concentration 2.Standard solution – the solution with known concentration

25. 3. Equivalence point - in a neutralization reaction, the point at which there are equal moles of hydronium and hydroxide ions 4. End point - the point in a titration where an indicator changes color 5. Primary standard - a highly purified compound, when used in solution to check the concentration of the known solution

26. 0.10 M HCl is titrated with NaOH. a)Determine the volume of each needed in the titration. b)Calculate the concentration of NaOH.

28. C. Molarity and Titration 1. Determine the moles of acid (or base) from the standard solution used during titration 2. From a balanced chemical equation, determine the ratio of moles of acid (base) to base (acid) 3. Determine the moles of solute of the unknown solution used during the titration 4. Determine the molarity of the unknown solution

29. D. Examples 1. In a titration of vinegar, you find that it requires 11.10 mL of 0.748M NaOH to neutralize a 10.0 mL sample of vinegar. What is the concentration of acetic acid in this sample of vinegar? NaOH + HC 2 H 3 O 2 →

30. 2. What is the molarity of a magnesium hydroxide solution if 45.45 mL of a 0.50M HCl solution is used to titrate 25 mL of magnesium hydroxide?