1. A 0.44 M aq solution of weak acid is 1.7% dissociated at equilibrium. Calculate value Ka for the acid
To calculate the value of Ka for the weak acid, we need to use the information provided about the concentration and degree of dissociation at equilibrium.
Given:
- The concentration of the weak acid solution is 0.44 M.
- The weak acid is 1.7% dissociated at equilibrium.
First, we need to determine the initial concentration of the weak acid at equilibrium. We can do this by assuming that x moles of the weak acid dissociate, resulting in x moles of hydronium ions (H3O+) and x moles of the conjugate base (A-) formed. Therefore, at equilibrium, the concentration of the weak acid will be its initial concentration (0.44 M) minus the amount that dissociated (x).
Since the weak acid is 1.7% dissociated at equilibrium, this means that x represents 1.7% of the initial concentration. We can convert this percentage to a decimal by dividing it by 100:
1.7% = 1.7/100 = 0.017
Now, we can set up an expression for the equilibrium constant (Ka) using the concentrations of the dissociated species:
Ka = [H3O+][A-] / [HA]
The concentration of H3O+ and A- is x, and the concentration of HA is (0.44 - x). Substituting these values into the equation:
Ka = (x)(x) / (0.44 - x)
Since x represents 0.017 times the initial concentration (0.44 M), we can substitute these values into the equation:
Ka = (0.017 * 0.44)(0.017 * 0.44) / (0.44 - 0.017 * 0.44)
Calculating this expression will give the value of Ka for the weak acid.