1. 1 The Chemistry of Acids and Bases –Finding pH and pOH

2. 2 HNO 3, HCl, H 2 SO 4 and HClO 4 are among the only known strong acids. Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION.

3. 3 Weak acids are much less than 100% ionized in water.Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH 3 CO 2 H Strong and Weak Acids/Bases

4. 4 Generally divide acids and bases into STRONG or WEAK ones.Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID: HNO 3 (aq) + H 2 O (l) ---> H 3 O + (aq) + NO 3 - (aq) HNO 3 is about 100% dissociated in water.

5. 5 Strong Base: 100% dissociated in water.Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) NaOH (aq) ---> Na + (aq) + OH - (aq) Strong and Weak Acids/Bases Other common strong bases include KOH and Ca(OH) 2. CaO + H 2 O --> Ca(OH) 2 CaO

6. 6 Weak base: less than 100% ionized in waterWeak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq) Strong and Weak Acids/Bases

7. 7 Weak Bases

8. 8 Calculating the pH pH = - log [H+] pH is a measure of the hydrogen ion concentration, [H+] (Remember that the [ ] mean Molarity) Example: If [H + ] = 1 X 10 -10 pH = - log 1 X 10 -10 pH = 10 Example: If [H + ] = 1.8 X 10 -5 pH = - log 1.8 X 10 -5 pH = 4.74

9. 9 Try These! Find the pH of these: 1) A 0.15 M solution of Hydrochloric acid 2) A 3.00 X 10 -7 M solution of Nitric acid H/O pH Practice Worksheet H/O pH Practice Worksheet

10. 10 Calculating the pOH pOH = -log [OH-] pOH is a measure of the hydroxide ion concentration, [OH-] Example: Find the pOH of a 0.1M NaOH solution pOH = -log(0.1) pOH = 1 pH + pOH = 14 Example: Find the pOH of a solution of HCl that has a pH of 3.4. pH = 3.4 pOH = 14 – 3.4 = 10.6

11. 11 Try These!! 1.Determine the pOH of a 0.0035 M HNO 3 solution. H/O pH and pOH Practice Worksheet

12. 12 pH calculations – Solving for H+ If the pH of Coke is 3.12, [H + ] = ??? Because pH = - log [H + ] then - pH = log [H + ] - pH = log [H + ] Take antilog (10 x ) of both sides and get 10 -pH = [H + ] [H + ] = 10 -3.12 = 7.6 x 10 -4 M *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button

13. 13 pH calculations – Solving for H+ A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution?A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? pH = - log [H + ] 8.5 = - log [H + ] -8.5 = log [H + ] Antilog -8.5 = antilog (log [H + ]) 10 -8.5 = [H + ] 3.16 X 10 -9 = [H + ] pH = - log [H + ] 8.5 = - log [H + ] -8.5 = log [H + ] Antilog -8.5 = antilog (log [H + ]) 10 -8.5 = [H + ] 3.16 X 10 -9 = [H + ]

14. 14 pH [H + ] [OH - ] pOH

15. 15 Water H 2 O can function as both an ACID and a BASE (amphoteric). In pure water there can be AUTOIONIZATION Equilibrium constant for water = K w K w = [H 3 O + ] [OH - ] = 1.00 x 10 -14 at 25 o C

16. 16 More About Water K w = [H 3 O + ] [OH - ] = 1.00 x 10 -14 at 25 o C In a neutral solution [H 3 O + ] = [OH - ] so K w = [H 3 O + ] 2 = [OH - ] 2 and so [H 3 O + ] = [OH - ] = 1.00 x 10 -7 M Autoionization

17. 17 The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H + ion concentration of the rainwater? The OH - ion concentration of a blood sample is 2.5 x 10 -7 M. What is the pH of the blood?

18. 18 Calculating [H 3 O + ], pH, [OH - ], and pOH Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 3.0 M and (b) 0.0024 M. Calculate the [H + ], pH, [OH - ], and pOH of the two solutions at 25°C. Problem 2: What is the [H + ], [OH - ], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral? Problem 3: Problem #2 with pH = 8.05?

19. 19 Cheat Sheet To find pH use: –log of M To find pOH: 14-pH To find [H+]: 2 nd log -pH To find [OH-]: 2 nd log -pOH