1. Chapter 16 More Work with Acids and Bases

2. 16.2 - pH Self-Ionization of Water: 2H 2 O H 3 O + + OH - -Occurs in 2 per 1 billion molecules in PURE (deionized or distilled) water H 2 O + H 2 O H 3 O + + OH -

3. Equilibrium constant of water 2H 2 O H 3 O + + OH - K w = 1 x 10 -14 = [OH - ][H 3 O + ] (will be given to Academic) Neutral (PURE) water: [OH-] = [H 3 O+] = 1 x 10 -7 M [ ] = Concentration in Molarity (mol solute / L solution)

4. Non-neutral water (water that has an acid or base added to it) If [OH-] > [H 3 O+] If [H 3 O+] >[OH-] Solution is ACIDIC Solution is BASIC

5. pH Scale pH = - log [H 3 O + ] (will be given to Academic) Typical scale is 1 – 14, but can be outside of this pH < 7 pH > 7 pH =7 Acidic Basic Neutral Practice Problem: If [H3O+] = 2.4 x 10 -5 M -We know solution is ACIDIC because [H3O+] >1 x 10 -7 M pH = - log (2.4 x 10-5 M) = 4.61

6. pOH = - log [OH-] (given to Academic) 14 = pH + pOH (given to Academic) Be careful of diprotic acids and bases with more than one hydroxide! You need to calculate the MOLES of the ION, not the entire compound before you calculate pH or pOH.

7. Examples: 1.[H+] = 2.3 x 10 -8 M Find: pH, pOH, [OH-], Acid or Base?

8. Examples: 2. 0.3 M H 2 SO 4 (I admit, the work we’re doing is SIMPLIFIED!) Find: pH, pOH, [OH-], Acid or Base?

9. Example: 3. 0.20 M Ba(OH) 2 Find: pH, pOH, [H 3 O+], Acid or Base?

10. Titrations – Combining an Acid + Base Indicator – Chemical that changes color based on pH Picking the correct indicator – Pick the indicator that changes color at the correct pH

11. Indicators IndicatorpH RangeAcidBase Thymol Blue1.2-2.8redyellow Methyl yellow2.9-4.0redyellow Methyl orange3.1-4.4redorange Bromphenol blue3.0-4.6yellowblue-violet Bromcresol green4.0-5.6yellowblue Methyl red4.4-6.2redyellow Bromcresol purple5.2-6.8yellowpurple Bromphenol blue6.2-7.6yellowblue Phenol red6.4-8.0yellowred Cresol red7.2-8.8yellowred Thymol blue8.0-9.6yellowblue Phenolphthalein8.0-10.0colorlessred Thymolphthalein9.4-10.6colorlessblue Color of indicator when BELOW LOWER pH Range value Color of indicator when ABOVE HIGHER pH Range value Example: Thymol Blue: When pH less than 1.2 When pH greater than 2.8 When pH between 1.2 – 2.8 Red Yellow Orange

12. Phenolphthalein Commonly used indicator In Acid = Colorless In Base = Pink

13. Endpoint vs. Equivalence Point Endpoint = The point at which the COLOR change happens. Equivalence Point = The point at which the MOLE Acid to MOLE Base ratio balances out. *We want the ENDPOINT to be as close to the EQUIVALENCE POINT as possible. (We’ll talk more about this soon!)

14. Titration Calculations Examples: Base Acid + Indicator (+ Extra Water)

15. Titration Calculations Examples:

16. pH Meter = Instrument that measure pH numerically. -Can be used to see change in pH throughout the titration.

17. Titration Curves A graph of pH versus volume of base added -Monitors pH over the entire titration **You will see a sharp increase in pH at the equivalence point**

18. Buret with Base pH meter Acid (Indicator optional) pH Titration Apparatus:

19. Strong Acid + Strong Base Start with a LOW pH – measuring ACID in beaker The Equivalence Point occurs at pH = 7.0

20. Why is the pH = 7.0?? Example: HCl + NaOH -> H 2 O + NaCl Strong Acid + Strong Base Strong Acid Strong Base Salt Water = NEUTRAL = pH = 7.0

21. Weak Acid + Strong Base On simulator: Change [NaOH] to 0.5 M The pH at the equivalence point is GREATER THAN 7

22. Weak Acid + Strong Base -The pH at the Equivalence Point is >7.0 (BASIC) -Why?? HCH 3 COO + NaOH -> H 2 O + NaCH 3 COO NaCH 3 COO -> Na + + CH 3 COO - CH 3 COO - + H 2 O HCH 3 COO + OH - This is the CONJUGATE BASE OF A WEAK ACID This makes the solution at the Equivalence Point BASIC

23. Weak Base + Strong Acid pH at Equivalence Point is < 7.0 (ACIDIC)

24. Weak Base + Strong Acid WHY?? NH 3 + HCl -> NH 4 +1 + Cl -1 NH 4 +1 + H 2 O NH 3 + H 3 O +1 Makes the solution a little ACIDIC Weak Base + Weak Acid Depends on which WEAK is stronger!

25. Titration Summary http://www.ausetute.com.au/titrcurv.html