Calculate the percent dissociation of acetic acid (Ka = 1.8 x 10-5) in a solution containing 0.00973 M CH3COOH and 0.0124 M K(CH3COO). Report your answer to 2 significant figures.
Thanks!
Calculate (H^+) in the buffered solution. Then percent ionization is
%ion = [((H^+)/0.00973] *100
how would i calculate the H+?
The easiest way is to use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/(acid)]
To calculate the percent dissociation of acetic acid, we need to know its initial concentration and the equilibrium concentration of the dissociated species.
The dissociation of acetic acid (CH3COOH) can be represented as follows:
CH3COOH ⇌ CH3COO- + H+
The equilibrium constant for this reaction is given by Ka = ([CH3COO-][H+]) / [CH3COOH]
First, let's calculate [H+] and [CH3COO-] at equilibrium using the initial concentrations and the assumption that the dissociation is small compared to the initial concentration.
Let x be the concentration of H+ (which is equal to the concentration of CH3COO- since 1 mol of H+ is formed for every 1 mol of CH3COO-).
At equilibrium, the concentration of CH3COOH (CH3COOH) will decrease by x, and the concentration of CH3COO- ([CH3COO-]) and H+ ([H+]) will increase by x.
Therefore, we can write the equilibrium concentrations as follows:
[CH3COOH] = 0.00973 M - x
[CH3COO-] = x
[H+] = x
Substituting these values into the equilibrium constant expression, we get:
Ka = (x * x) / (0.00973 - x)
Assuming that x is small compared to 0.00973, we can neglect x in the denominator and simplify the expression:
Ka ≈ (x * x) / 0.00973
Rearranging the equation to solve for x:
x * x = Ka * 0.00973
x = √(Ka * 0.00973)
Now, we can calculate x using the given Ka value and the initial concentrations:
Ka = 1.8 x 10^-5
x = √(1.8 x 10^-5 * 0.00973)
x = 0.0004741
The percent dissociation is given by the ratio of the concentration change to the initial concentration, multiplied by 100:
Percent Dissociation = (x / 0.00973) * 100
Substituting the value of x, we find:
Percent Dissociation = (0.0004741 / 0.00973) * 100 = 4.87
Therefore, the percent dissociation of acetic acid is 4.87%, which should be reported to 2 significant figures.