{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Acids and Bases2

Acids and Bases2 - AdditionalAspectsof AqueousEquilibria...

Info iconThis preview shows pages 1–15. Sign up to view the full content.

View Full Document Right Arrow Icon
Additional Aspects of Aqueous Equilibria David A. Katz Department of Chemistry Pima Community College
Background image of page 1

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

View Full Document Right Arrow Icon
The Common Ion Effect The Common Ion Effect Consider a solution of acetic acid: HC 2 H 3 O 2( aq ) + H 2 O ( l ) H 3 O + ( aq ) + C 2 H 3 O 2 ( aq) If acetate ion is added to the solution, Le Châtelier’s Principle says the equilibrium will shift to the left Principle says the equilibrium will shift to the left. Acetate ion can be added in the form of a strong electrolyte such as sodium acetate Na C H O electrolyte such as sodium acetate, Na C 2 H 3 O 2 Na C 2 H 3 O 2 (aq) Na + (aq) + C 2 H 3 O 2 (aq) Sodium acetate is 100% ionic in solution
Background image of page 2
The Common Ion Effect The Common Ion Effect The extent of ionization of a weak electrolyte can be decreased by adding a strong electrolyte to the solution that has an ion in common with the weak electrolyte.
Background image of page 3

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

View Full Document Right Arrow Icon
The Common Ion Effect The Common Ion Effect Example: Calculate the fluoride ion concentration and pH of a solution that is 0.20 M in HF and 0.10 M in HCl. K a for HF is 6.8 10 4 . Solution: HF (aq) + H 2 O (l) H 3 O + (aq) + F (aq) The equilibrium constant expression is [H 3 O + ] [F ] [HF] K a = = 6.8 10 4
Background image of page 4
The Common Ion Effect The Common Ion Effect Because HCl, a strong acid, is also present, HCl (aq) + H 2 O (l) H 3 O + (aq) + Cl - (aq) the initial [H O + ] is not 0 but rather 0 10 M the initial [H 3 O ] is not 0, but rather 0.10 . [HF], M [H 3 O + ], M [F ], M Initial concentration 0.20 0.10 (from the HCl) 0 Ch Change x + x + x Equilibrium concentration 0.20 x 0 20 0.10 + x 0 10 x 0.20 0.10 Remember, x is small and can be ignored
Background image of page 5

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

View Full Document Right Arrow Icon
The Common Ion Effect The Common Ion Effect (0.10) ( x ) (0.20) 6.8 10 4 = Solve for x. Rearrange to: = x (0.20) (6.8 10 4 ) (0.10) 1.4 10 3 M = x
Background image of page 6
The Common Ion Effect The Common Ion Effect Therefore, [F ] = x = 1.4 10 3 M If we add x to 0.10 M [H 3 O + ] = 0.10 + x = 0.10 + (1.4 10 3 ) = 0.10 M and pH = log (0.10) pH = 1.00
Background image of page 7

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

View Full Document Right Arrow Icon
Buffer Solutions A buffer is an li i f h application of the common ion effect B th Because the common ion shifts the equilibrium in one direction, a buffer is resistant to pH changes, even when small amounts of a strong id b i dd d acid or base is added.
Background image of page 8
Buffer Solutions If a small amount of hydroxide is added to an equimolar solution of HF in NaF, for example, the HF reacts with the OH to make F and water.
Background image of page 9

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

View Full Document Right Arrow Icon
Buffer Solutions If acid is added, the F reacts to form HF and water.
Background image of page 10
Buffer Calculations Consider the equilibrium constant expression for the dissociation of a generic acid, HA: HA + H O H O + + A [H 3 O + ] [A ] [HA] K a = HA + H 2 O H 3 O + A Rearrange this to separate out the [H 3 O + ] [A ] [HA] K a = [H 3 O + ]
Background image of page 11

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

View Full Document Right Arrow Icon