calculate the % dissociation of a 0.750M acetic acid solution and 0.50 M sodium acetate solution.
I got the % for acetic acid to be 0.48% but cant finish the question.
Short cut...
________
[H+]= √Ka[Acid]
_____________
= √1.75E-5[0.750] M
= 0.0036M
%Ionization = ([H+]/[HOAc])100%
=[(0.0036)/(0.750)]100% = 0.48% is correct for pure water, but NaOAc provides a common ion that reduces the %ionization. Use the Ice table
HOAc <=> H + OAc
Ceq 0.75 X .50
Ka = [H][OAc]/[HOAc] = [(x)(0.50)]/(0.750) = 1.75E-5
Solve for x = 2.625E-5 M = [H]
%Izn = [(2.625E-5)/(0.750)]100%
=0.0035%
To calculate the percent dissociation of a solution, you need to know the initial molar concentration of the solute and the equilibrium concentration of the dissociated species. In this case, we have two different solutions: a 0.750M acetic acid solution and a 0.50M sodium acetate solution.
To determine the percent dissociation of acetic acid, we need to calculate the equilibrium concentration of the dissociated species (acetate ion) and then use it to find the percentage dissociation.
The chemical equation for the dissociation of acetic acid is:
CH3COOH ⇌ CH3COO- + H+
Since acetic acid is a weak acid, it partially dissociates in solution. Let's assume that at equilibrium, x moles of acetic acid dissociate, and x moles of acetate ion are formed. Therefore, the equilibrium concentration of acetate ion is x M.
To calculate the value of x, we can use the expression for the acid dissociation constant, Ka, which is given by:
Ka = [CH3COO-][H+] / [CH3COOH]
The concentration of acetic acid, [CH3COOH], is given as 0.750 M, and the concentration of sodium acetate, [CH3COO-], is 0.50 M (since sodium acetate dissociates completely). The concentration of H+ ions can be assumed to be negligible compared to the other two species.
Substituting these values into the Ka expression:
Ka = (x)(x) / (0.750 - x)
Simplifying:
Ka = x^2 / (0.750 - x)
The value of Ka for acetic acid is 1.8 x 10^-5.
Now, we can solve the quadratic equation to find the value of x:
1.8 x 10^-5 = x^2 / (0.750 - x)
Multiply both sides by (0.750 - x) to get rid of the denominator:
1.8 x 10^-5 (0.750 - x) = x^2
Now, expand and rearrange to obtain a quadratic equation:
1.350 x 10^-5 - 1.8 x 10^-5 x = x^2
Rearrange to the standard quadratic form:
x^2 + 1.8 x 10^-5 x - 1.350 x 10^-5 = 0
Solving this quadratic equation for x will give you the value of x, which represents the concentration of acetate ions at equilibrium. Once you have determined x, you can calculate the percent dissociation as follows:
% dissociation = (x / 0.750) * 100
Plug in the value of x into this equation to obtain the percent dissociation of acetic acid in the 0.750M solution.