Aspirin is a monoprotic weak acid with a K a of 3.98 x 10-4 and one dose of aspirin is 500mg.

Write the reaction that controls the pH of aspirin (HC9H7O4)

Given that the average stomach has a pH of 1.4 and a volume of approximately 1 liter, calculate the concentration of aspirin (HA) and its conjugate (A - ) in the stomach.

The conjugate of aspirin is the active drug, and it is absorbed from the stomach into the bloodstream. The pH of the blood stream is 7.4.

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Keith LeannonLv2

2 Oct 2019

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Related questions

For the dissociation reaction of a weak acid in water,

HA(aq)+H2O(l)âH3O+(aq)+Aâ(aq)

the equilibrium constant is the acid-dissociation constant, Ka, and takes the form

Ka=[H3O+][Aâ][HA]

Weak bases accept a proton from water to give the conjugate acid and OHâ ions:

B(aq)+H2O(l)âBH+(aq)+OHâ(aq)

The equilibrium constant Kb is called the base-dissociation constant and can be found by the formula

Kb=[BH+][OHâ][B]

When solving equilibrium-based expression, it is often helpful to keep track of changing concentrations is through what is often called an I.C.E table, where I. stands for Initial Concentration, C. stands for Change, and E. stands for Equilibrium Concentration. To create such a table, write the reaction across the top creating the columns, and the rows I.C.E on the left-hand side.

Initial (M)Change (M)Equilibrium (M)A+ BâAB

Part A

Aspirin (acetylsalicylic acid, C9H8O4) is a weak monoprotic acid. To determine its acid-dissociation constant, a student dissolved 2.00 g of aspirin in 0.600 L of water and measured the pH. What was the Ka value calculated by the student if the pH of the solution was 2.60?

Express your answer numerically using two significant figures.

Hints

Ka =

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You used the initial concentration of aspirin in the Ka expression. Instead, you need to use the equilibrium concentration. Consider that the amount of aspirin that reacted is equal to the amount of H₃O⁺ produced. How much is left over?

Part B

A 0.100 M solution of ethylamine (C2H5NH2) has a pH of 11.87. Calculate the Kb for ethylamine.

Express your answer numerically using two significant figures.

Hints

Kb =