Acetic acid CH 3 COOH is a weak acid with K a 18 x 10 5 What amount of sodium

Acetic acid ch 3 cooh is a weak acid with k a 18 x 10

This preview shows page 21 - 25 out of 85 pages.

20. Acetic acid, CH3COOH, is a weak acid with Ka= 1.8 x 10-5. What amount of sodium acetate, CH3COONa, must be dissolved in 250.0 mL of 0.30 M CH3COOH, in order to produce a buffer with pH = 4.60? (a) 0.12 mol (b) 0.054 mol (c) 0.022 mol (d) 0.015 mol (e) 0.078 mol 0.30 M HA Ka= 1.8 x 10-5[A-] = ? pH = 4.60; [H+] = 10-4.60= 2.51 x 10-5HA + H2O H3O++ A -
Image of page 21
22 HA + H2O H3O++ Initial 0.30 Change Equilibrium 2.51 x 10-5HA + H2O H3O++ Initial 0.30 0 Change -X +X Equilibrium 0.30 - X 2.51 x 10-5Y + X X = 2.51 x 10-5HA + H2O H3O++ Initial 0.30 0 Change -2.51 x 10-5+2.51 x 10-5+2.51 x 10-5Equilibrium 0.30-2.51 x 10-52.51 x 10-5Y + 2.51 x 10-5([H3O+][A-])/[HA] = Ka([2.51 x 10-5][Y +(2.51 x 10-5)])/[0.30 – (2.51 x 10-5)] = 1.8 x 10-5Due to small Ka, assume that 2.51 x 10-5is very small and can be dropped. Therefore, [HA] = 0.30; [A-] = Y ([2.51 x 10-5][Y])/[0.30] = 1.8 x 10-5(((([2.51 x 10-5] x [Y])/[0.30]) = (1.8 x 10-5)),X) Y = 0.215mol/L = 0.0538 mol/0.250L TITRATIONS and INDICATORS A - Y A - Y +X A - Y
Image of page 22
23 21 Chem 162-2011 Final exam Chapter 15b – Applic. of Acid & Base Equilibria (Buffers & Titrations) Titrations and indicators Which one of the indicators below would be best to use when titrating 0.1M morphine (Kb= 1.6x10-6) with 0.3M HCl? + O 0 O + 0 +X X X
Image of page 23
Image of page 24
Image of page 25

You've reached the end of your free preview.

Want to read all 85 pages?

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture