lecture+g

# lecture+g - Ch 11 Acids and bases Calculating the pH of...

This preview shows pages 1–4. Sign up to view the full content.

Ch 11 – Acids and bases Calculating the pH of acidic/basic solutions 2 – Aqueous weak acid or weak base solutions In the case of weak acids/bases, we’ll need to remember the dissociation does not favor the conjugate ions, but rather the un-ionized acids/bases, and we’ll need to use the value of K a or K b to determine [H 3 O + ] eq . Practice problem #20 Hydrofluoric acid has a K a of 7.2 × 10 4 . What is the pH of 3.44 M aqueous HF? Since we have K a , we know the reaction in question is: HF(aq) + H 2 O(l) H 3 O + (aq) + F (aq) K a = 7.2 × 10 4 I C E 3.44 N/A 10 7 (~0) 0 x N/A +x +x 3.44 x x x At equilibrium, we have: x 2 3.44 x = 7.2 × 10 4 ( 3.44) x 2 3.44 7.2 × 10 4 x = 0.050 M ([H + ] eq ) pH = log(0.05) = 1.30

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Ch 11 – Acids and bases Now that we know how to determine [H 3 O + ] eq for an acid, we can discuss another measure of how many ions have been produced by an acid, the PERCENT IONIZATION . This is defined as follows: % ionization = [H 3 O + ] eq [HA] 0 × 100% Some trends to keep in mind about percent ionization: - for the same [HA] 0 , stronger acids will have higher percent ionization. - more dilute solutions of the same acid will have higher percent ionization. The increase in percent ionization upon a simple dilution is actually an example of Le Châtelier’s principle. Before dilution, there are a certain number of particles (H + , A , and HA) floating around in a certain volume, establishing a certain particles to volume ratio. The number of particles is dependent on K a . After dilution, there are still the same number of particles as before but a larger volume. To adjust to this change in the particles to volume ratio, the system shifts to make more particles, which is towards ioniziation.
Ch 11 – Acids and bases Practice problem #21 Calculate the pH of a aqueous solution containing 2.47 M ethylamine (C 2 H 5 NH 2 ) and 4.22 M pyridine (C 5 H 5 N), and determine the concentration of all aqueous phase ions present at equilibrium. We should first determine what reactions are present which will control the pH

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 11

lecture+g - Ch 11 Acids and bases Calculating the pH of...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online