1. Acid-Base Titration & pH

2. 16-1 Objectives Describe the self-ionization of water
Define pH and give the pH of a neutral solution at 25oC
Explain and use the pH scale
Given concentrations of H+ & OH-, calculate pH
Given pH, calculate concentrations of H+ & OH-

3. Self-Ionization of Water
Two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton
Conductivity shows concentrations of H3O+ and OH- are 1.0 x 10-7 mol/L at 25oC
Kw = [H3O+][OH-] = 1.0 x M2

4. Self-Ionization of Water

5. Neutral, Acidic, and Basic Solutions
Neutral solutions: have equal [H+] and [OH-]
Acidic Solutions: have greater [H+] than [OH-]
Basic Solutions (alkaline): have greater [OH-] than [H+]

6. Calculating [H+] and [OH-]
Kw = [H+] [OH-]
If given the concentration of one ion, the concentration of the other can be calculated

7. HNO3(l) + H2O(l)  H3O+(aq) + NO3-(aq)
Example
A 1.0 x 10-4 M solution of HNO3 has been prepared for a lab experiment. Calculate [H3O+] and [OH-]
HNO3 is a strong acid so assume 100% dissociation
HNO3(l) + H2O(l)  H3O+(aq) + NO3-(aq)

8. Solution Given: Kw = [H+] [OH-] 1.0 x 10-4 M HNO3
Find concentration of H+:

9. Solution Solve algebraically: Substitute:
Complete practice problems 1-4 on page 484 out of the text.

10. pH Scale pH – pouvior hydrogène or “hydrogen power”
pH is defined as the negative logarithm of the hydronium ion concentration [H3O+]
To calculate pH
pH = -log[H3O+] or
pH = -log[H+]

11. pH Scale To calculate pOH pOH = -log[OH-]
At 25oC, [H+] = [OH-] = 1.0 x 10-7 = pH =7
If [H+] > [OH-] the solution is acidic
If [OH-] > [H+] the solution is basic

12. Stop Here

13. Examples: What is the pH of 1.0 x 10-3 M NaOH solution?
What is the pH of a solution if the [H3O+] is 3.4 x 10-5 M?
Determine the [H3O+] of an aqueous solution that has a pH of 4.0.
The pH of a solution is found to be 7.52.
Find [H3O+]
Find [OH-]
Is the solution acidic or basic?
These are all practice problems from the text book.

17. 16-2 Objectives Describe how a pH indicator works
Explain an acid-base titration
Calculate molarity of a solution from titration data

18. Indicators and pH Meters
Acid-Base Indicator – compounds whose colors are sensitive to pH
In acidic solutions, In- ions act as B-L bases
In basic solutions, OH- react with H+ from indicator

19. Indicators
Transition Interval – the pH range over which an indicator changes color
Universal Indicators – combination of different indicators
pH meters – determine pH by measuring the voltage difference between two electrodes

20. Titrations
The controlled addition of a measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of an unknown concentration
Equivalence Point – the point in a titration where [H+] and [OH-] are present in chemically equivalent amounts
End Point – the point of the titration at which the indicator changes color

22. End here

23. Molarity and Titration
Standard Solution – the solution that contains the precisely known concentration of a solute
Primary Standard – a highly purified solid compound used to check the concentration of the known solution in a titration

24. Calculating Molarity from Titration Data
Write balanced chemical equation and determine chemical equivalents
Determine moles of acid or base from the known solution used during the titration
Determine moles of solute of the unknown used during the titration
Determine molarity

25. Example: in a titration, 27. 4 mL of 0. 0154 M NaOH is added to a 20
Example: in a titration, 27.4 mL of M NaOH is added to a 20.0 mL sample of HCl solution of unknown concentration…find the molarity of the acid solution

26. Solution

27. A 15. 5 mL sample of 0. 215 M KOH solution required 21
A 15.5 mL sample of M KOH solution required 21.2 mL of aqueous acetic acid solution in a titration experiment. Calculate the molarity of the acetic acid solution.

28. Solution

29. By titration, 17. 6 mL of aqueous H2SO4 neutralized 27. 4 mL of 0
By titration, 17.6 mL of aqueous H2SO4 neutralized 27.4 mL of M LiOH solution. What was the molarity of the aqueous acid solution?

30. Solution