For 0.100 M of weak acid (propanoic acid HPr) the Ka is given by 1.30 x10-5 , calculate the pH of the sample.
HPr ==> H^+ + Pr^-
Set up an ICE chart.
Ka = (H^+)(Pr^-)/(HPr)
Solve for (H^+) and convert to pH.
Post your work if you get stuck.
To calculate the pH of a weak acid solution, we need to use the equilibrium expression for the dissociation of the acid and solve for the concentration of hydrogen ions (\([H^+]\)).
The dissociation of propanoic acid (HPr) can be represented as follows:
HPr ⇌ H+ + Pr-
The equilibrium expression for this dissociation is defined by the acid dissociation constant (Ka):
Ka = [H+][Pr-] / [HPr]
Given that the concentration of the weak acid HPr is 0.100 M and the Ka value is 1.30 x 10^-5, we can set up the following equation:
Ka = [H+][Pr-] / [HPr]
Since HPr dissociates into H+ and Pr-, and we assume that [Pr-] is negligible compared to [H+], we can make the approximation that [H+] ≈ [HPr].
Now, we can express Ka as [H+]^2 / [HPr] and substitute the known values:
1.30 x 10^-5 = ([H+]^2) / 0.100
To solve this equation for [H+], we can rearrange it:
[H+]^2 = 1.30 x 10^-5 * 0.100
[H+]^2 = 1.30 x 10^-6
[H+] ≈ √(1.30 x 10^-6)
Using a calculator, we find that [H+] ≈ 3.61 x 10^-4 M.
To find the pH, we can take the negative logarithm of the [H+] concentration:
pH = -log[H+]
pH = -log(3.61 x 10^-4)
Using a calculator, we find that the pH is approximately 3.44 for the 0.100 M weak acid solution of propanoic acid (HPr).