1. Hydrolysis of Salts December 2015

2. What we know so far…. Bronsted-Lowry AcidsBronsted-Lowry Bases Donate H + (protons) Criteria to be an acid: Must have an H + to give away K a > 10 -14 Can be neutral (HNO 2 ), positive (NH 4 + - the conj acid of NH 3 ) or negative (HSO 3 - - the second ionization of H 2 SO 3) Accept H + (protons) Criteria to be a base: Must have a lone pair of electrons in order to attract an H + K b > 10 -14 *see next slide Can be neutral (NH 3 ) or negative (CN - ) but NEVER positive

3. Why > 10 -14 ? Consider Cl - : Problem: can’t act as an base because HCl is a strong acid K b is too small (K b = ___); won’t make enough OH - to influence the pH Consider the base B with K b = 1x10 -15 B (aq) + H 2 O  BH + (aq) + OH - (aq) E 0.10-x x x Calculate x, pOH and pH. What is unusual about your answer?

4. Salts What are salts? Recall the 2 products that are formed when an acid and a base react: Acid + Base  ______ + ______ i.e. KOH (aq) + HBr (aq)  KBr (aq) + H 2 O (l) Salts: are ionic compounds that completely dissociate in water water surrounds all anions and cations Can these ions interact with the surrounding water like acids and bases do?

5. Hydrolysis of Salts Consider the following salt solutions: NaCl (aq) pH = 7 NaNO 2(aq) pH > 7 NH 4 Cl (aq) pH < 7 Conclusion: something in the NaNO 2 solution is accepting H + from H 2 O to produce OH - something in the NH 4 Cl solution is donating H + to H 2 O to produce H 3 O + nothing is donating/accepting H + in the NaCl solution.

6. Consider the basic nature of NaNO 2 and the criteria to be a base. What part of NaNO 2 is acting as a base? Write the ionization reaction that represents this. What is the K b for NO 2 - ? What is the pH of a 0.10M solution of NaNO 2 ?

7. Consider the acidic nature of NH 4 Cl and the criteria to be an acid. What part of NH 4 Cl is acting as an acid? Write the ionization reaction that represents this. What is K a for NH 4 + ? What is the pH of a 0.25M NH 4 Cl solution?

8. Consider the neutral nature of NaCl. Why are Na + or Cl - unable to interact with water that surrounds them?

9. Hydrolysis of Salts When anions or cations or BOTH in a salt solution interact with the water that surrounds them to produce acidic or basic solutions.