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Mixing weak acids

Mixing weak acids. Calculate the pH of a solution that contains 1.00 M HCN ( K a = 6.2 x10 -10 ) and 5.00 M HNO 2 ( K a = 4.0 x 10 -4 ). Also calculate the concentration of cyanide ion (CN - ) in this solution at equilibrium. Percent Dissociation.

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Mixing weak acids

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  1. Mixing weak acids • Calculate the pH of a solution that contains 1.00 M HCN (Ka = 6.2 x10-10) and 5.00 M HNO2 (Ka= 4.0 x 10-4). Also calculate the concentration of cyanide ion (CN-) in this solution at equilibrium.

  2. Percent Dissociation • For a given weak acid, the percent dissociation increases as the acid becomes more dilute.

  3. Problem • Calculate the percent dissociation of acetic acid (Ka = 1.8 x 10-5) in each of the following solutions. • a) 1.00 M HC2H3O2 • b) 0.100 M HC2H3O2

  4. Problem • Lactic acid (HC3H5O3) is a waste product that accumulates in muscle tissue during exertion, leading to pain and a feeling of fatigue. In a 0.100 M aqueous solution, lactic acid is 3.7% dissociated. Calculate the Ka for this acid.

  5. Bases Chapter 14

  6. Bases • Bases produce hydroxide by Arrhenius • Hydroxides are not very soluble compounds. • The only hydroxides that are soluble are group 1 elements, and calcium, barium and strontium. • LiOH, RbOH and CsOH are significantly more expensive than the other compounds so they are rarely used. • Group 2 metal compounds are significantly less soluble than group 1.

  7. Strong Bases these make a lightning bolt on the periodic table!

  8. Base dissociation constant • For some base B • B + H2O BH+ + OH- (aq) • The Base Dissociation Constant (Kb) • Kb = [BH+] [OH-] • [B]

  9. The pH of Strong Bases. • This works the same as the pH of a strong acid. • Calculate the pH of a 5.00 x 10-2 M NaOH solution.

  10. pH of weak bases • Calculate the pH for a 15.0 M solution of NH3 (Kb = 1.8 x 10-5).

  11. More pH of a weak base • Calculate the pH of a 1.0 M solution of methylamine (Kb = 4.38 x 10-4).

  12. Another problem • Pyridine (C5H5N), an important solvent and base in organic syntheses, has a pKb of 8.77. What is the pH of 0.10 M pyridine?

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