   # About this time, you may be wishing you had an aspirin. Aspirin is an organic acid with a K a of 3.27 × 10 −4 for the reaction. HC 9 H 7 O 4 (aq) + H 2 O(ℓ) ⇄ C 9 H 7 O 4 − (aq) + H 3 O + (aq) If you have two tablets, each contains 0.325 g of aspirin (mixed with a neutral “binder” to hold the tablet together), and you dissolve then in a glass of water to give 225 mL of solution, what is the pH of the solution. ### Chemistry & Chemical Reactivity

9th Edition
John C. Kotz + 3 others
Publisher: Cengage Learning
ISBN: 9781133949640

#### Solutions

Chapter
Section ### Chemistry & Chemical Reactivity

9th Edition
John C. Kotz + 3 others
Publisher: Cengage Learning
ISBN: 9781133949640
Chapter 16, Problem 83GQ
Textbook Problem
30 views

## About this time, you may be wishing you had an aspirin. Aspirin is an organic acid with a Ka of 3.27 × 10−4 for the reaction.HC9H7O4(aq) + H2O(ℓ) ⇄ C9H7O4−(aq) + H3O+(aq)If you have two tablets, each contains 0.325 g of aspirin (mixed with a neutral “binder” to hold the tablet together), and you dissolve then in a glass of water to give 225 mL of solution, what is the pH of the solution.

Interpretation Introduction

Interpretation:

pH of the solution has to be determined which is prepared by the 0.325g of aspirin is dissolved in 225 ml of water.

Concept introduction:

Equilibrium constants:

The equilibrium constant is used to quantitative measurement of  the strength of the acid and bases in the water .

Ka is an acid constant for equilibrium reactions.

HA + H2OH3O++ A-Ka[H3O+][A-][HA]

Kb is a base constant for equilibrium reaction.

BOH + H2OB++ OH-Ka[B+][OH-][BOH]

Ion product constant for wter  Kw= [H3O+][OH-]       =1.00×10-14 pH = -log[H3O+]pOH= -log[OH-]Reltion between pH and pOH pH + pOH =14

### Explanation of Solution

Let’s calculate the concentration of aspirin:

Given mass of aspirin =0.325g

Mass of two aspirin tablets =  0.325g HC9H7O41 tablet HC9H7O4 × 2 tablets HC9H7O4= 0.65g  HC9H7O4

Convert the volume millilitres into litre.

Given volume =225mL

= 225mL × 1L1000mL= 0.225L

Concentration of aspirin =moles of aspirinVolume of solution(L)=(0.65g180g/mol)0.225L=1.6×10-2M

Therefore, concentration of aspirin is 1.6×10-2 M.

Aspirin interacts with water. The equilibrium chemical reaction is as follows.

HC9H7O4(aq) + H2O(l) C9H7O4-(aq) + H3O+(aq)

The equilibrium expression:

Ka[C9H7O4-][H3O+][HC9H7O4]

Enter the ICE table the concentrations before equilibrium is established, the change that occurs as the reaction proceeds to equilibrium and the concentrations when equilibrium has been achieved.

HC9H7O4(aq) + H2O(l) C9H7O4-(aq) + H3O+(aq)I       1.6×102                 --                --                  --C          -x                        --              + x               + xE    (1

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