Water Dissociation H 2 O (l) + 59kJ ↔ H + (aq) + OH - (aq)

Acids and bases are really just aqueous solutions of H + or OH -, so they just shift the water dissociation equation left to a certain extent. Kw = [H + ][OH - ] = 1.0x10 If you know the [H + ] or the [OH - ] you can calculate the other one.

H 2 O (l) + 59kJ ↔ H + (aq) + OH - (aq) In pure water… [H + ] = [OH - ] Kw = 1.0x = [H + ][OH - ] Kw = 1.0x = x 2  [H + ] = 1.0x10 -7 M That’s M This is a very small value, especially in comparison to the H + or OH - contributed by the presence of a strong acid or base.

H 2 O (l) + 59kJ ↔ H + (aq) + OH - (aq) Example: What is the [OH - ] in a 0.075M HNO 3 solution? Kw = 1.0x = [H + ][OH - ]  [OH - ] = [OH - ] = 1.3x M

Ka and Kb Keq’s for weak acids or bases reacting with water HF (aq) + H 2 O (l) ↔ H 3 O + (aq) + F - (aq) Ka = NH 3(aq) + H 2 O (l) ↔ NH 4 + (aq) + OH - (aq) Kb = You can look up Ka values, but not Kb’s

Conjugates… HF + H 2 O ↔ H 3 O + + F - F - + H 2 O ↔ HF + OH - Ka = Kb = For Conjugates…

Acids react with Bases… B-L equil form when WA reacts with WB HF + NH 3 ↔ F - + NH 4 + Keq large (>1)  products favoured Keq small  reactants favoured We can only compare the strength of the acids (look up Ka values)

HF + NH 3 ↔ F - + NH Keq = Ka(reactant acid) Ka(product acid) Keq =

Questions… That takes you up to #45…

pH pH is the “power” of Hydrogen (the exponent of the [H + ] ). Assuming it was represented as [H + ]= 10 x 4. pH = -log[H + ] 5. [H + ] = 10 -pH

pH = -log[H + ] and [H + ] = 10 -pH Example: What is the [OH - ] in a 0.075M HNO 3 solution? What is the pH? pH = -log(0.075) = 1.12 Note: in pH (or any logged value) numbers in front of the decimal place are not considered to be significant figures. pH = 1.12 has 2s.f. The numbers in front of the decimal are place holders and tell you how many zeros are in front of the digits.

pH = -log[H + ] and [H + ] = 10 -pH Example: What is the [OH - ] in a 0.075M HNO 3 solution? What is the pH? What is the pOH? pOH = -log(1.333x ) = Remember the pH = 1.12, what do you notice? 6. pH + pOH = 14 or pH + pOH = pKw

What is the pOH of 3.27x10 -4 M HI? What is the [H + ] in a solution with pH= 5.52 ? What is the [OH - ] in a solution with pH = 1.72

If the pH = , what are the [H + ], pOH, and [OH - ] ?

Acid/Base Formula Sheet 1. Kw = [H + ][OH - ] = 1.0x10 2. For conjugates, Ka x Kb = Kw 3. Keq = Kar Kap 4. pH = -log[H + ] 5. [H + ] = 10 -pH 6. pH + pOH = pKw (=14 7. There will more…

The pH Scale

Do the following questions now… Up to 56a according to the purple sheet.