Multiple Choice
Which Bronsted-Lowry base has the greatest concentration of hydroxide ions?
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17. Acid and Base Equilibrium
Ka and Kb
Multiple Choice
Determine the pH of 0.450 M HC7H5O2. The Ka for HC7H5O2 is 6.5 × 10−5.
A
0.35
B
2.27
C
3.27
D
4.19
E
4.53
Verified step by step guidance1
Identify the chemical species involved: HC7H5O2 is a weak acid, and its dissociation in water can be represented by the equation: HC7H5O2 ⇌ H+ + C7H5O2−.
Write the expression for the acid dissociation constant (Ka): Ka = [H+][C7H5O2−] / [HC7H5O2].
Set up an ICE (Initial, Change, Equilibrium) table to determine the concentrations of the species at equilibrium. Initially, [HC7H5O2] = 0.450 M, and [H+] and [C7H5O2−] are 0 M.
Assume that the change in concentration of HC7H5O2 is 'x' as it dissociates, so at equilibrium, [HC7H5O2] = 0.450 - x, [H+] = x, and [C7H5O2−] = x.
Substitute the equilibrium concentrations into the Ka expression: 6.5 × 10^−5 = (x)(x) / (0.450 - x). Solve for 'x' to find the concentration of H+, and then calculate the pH using the formula: pH = -log[H+].
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