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Equal volumes of 0.362 M aqueous solutions of acetylsalicylic acid (aspirin) (HC

ID: 1026164 • Letter: E

Question

Equal volumes of 0.362 M aqueous solutions of acetylsalicylic acid (aspirin) (HC9H704(aq)) and sodium acetate (NaCH3COO) are mixed. (1) Write the net ionic equation for the overall reaction that takes place as the system comes to equilibrium Write acetic acid, benzoic acid or formic acid and their conjugates in the form RCOOH RCOO. For example, benzoic acid should be written "C6HsCOOH" NOT "C&HsCO2H;". It is not necessary to include states such as (aq). (2) What is the value of the equilibrium constant for this reaction? (3) What is the pH of the resulting solution? Use the Tables link on the toolbar for any equilibrium constants that are required.

Explanation / Answer

1) C6H4(COOH)OCOCH3 + CH3COONa --> C6H4(OCOCH3)2 + CO2 + NaOH

(aspirin) (sodium acetate) (o-diacetylsalicylic acid)

2) The equilibrium constant, K can be calculated from - Kc = [C6H4(OCOCH3)2]*[CO2]*[NaOH] / [C6H4(COOH)OCOCH3]*[CH3COONa].

Since, carbon dioxide is in gaseous state and we don't know its partial pressure, it is not possible to calculate the value of Kc.

3) The pH of the resulting reaction mixture would be high because of the generation of sodium hydroxide which is a strong base.