A certain weak acid, HA, has a K_a value of 5.4 Times 10^-7. Calculate the perce

Question

A certain weak acid, HA, has a K_a value of 5.4 Times 10^-7. Calculate the percent dissociation of HA in a 0.10 M solution. Express your answer as a percent using two significant figures. Calculate the percent dissociation of HA in a 0.010 M solution. Express your answer as a percent using two significant figures A new potential heart medicine, code-named X-281, is being tested by a pharmaceutical company, Pharma-pill. As a research technician at Pharma-pill, you are told that X-281 is a monoprotic weak acid, but because of security concerns, the actual chemical formula must remain top secret. The company is interested in the drug's K_a value because only the dissociated form of the chemical is active in preventing cholesterol buildup in arteries. To find the pK_A of X-281, you prepare a 0.078 Mtest solution of X-281 at 25.0 ^degree C. The pH of the solution is determined to be 2.40. What is the pK_a of X-281? Express your answer numerically.

Explanation / Answer

%ion = [H+]/M *100

Ka = [H+][A-]/[HA]

[H+] = [A-] = x

[HA] = 01.-x

Ka = 5.4*10^-7

substitute

Ka = [H+][A-]/[HA]

5.4*10^-7= x*x/(0.1-x)

[H+] = 2.32*10^-4

%ion = [H+]/M *100 = (2.32*10^-4)/0.1 *100 = 0.0232 %

B)

similar to A

Ka = [H+][A-]/[HA]

5.4*10^-7= x*x/(0.01-x)

x = 7.32*10^-5

%ion = [H+]/M *100 = (7.32*10^-5)/0.01 *100 = 0.732%

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