Phenylacetic acid (C6H5CH2COOH) is one of the substances that accumulates in the blood of people with phenylketonuria, an inherited disorder that can cause mental retardation or even death. A 0.021 M solution of C6H5CH2COOH has a pH of 2.99. Calculate the Ka value for this acid.
what equation do i use?
Call that long name HP (which doesn't have anything to do with pH).
pH = 2.99
2.99 = -log(H^+)
(H^+) = 0.00102
.........HP ==> H^+ + P^-
I.....0.021.....0......0
C........-x.....x.....x
E......0.021-x..x.....x
Ka = (H^+)(P^-)/(HP)
Substitute 0.00102 for x and 0.021-0.00102 for HP and solve for Ka.
Whi i get fired tho
To calculate the Ka value for this acid, you will need to use the equation for the dissociation of the acid in water:
C6H5CH2COOH ⇌ C6H5CH2COO- + H+
The Ka expression for this reaction is:
Ka = [C6H5CH2COO-][H+] / [C6H5CH2COOH]
where [C6H5CH2COO-] represents the concentration of the conjugate base and [H+] represents the concentration of the hydrogen ions (protons).
To calculate the Ka value for phenylacetic acid (C6H5CH2COOH), we need to use the equation for the dissociation of the acid in water. The equation is as follows:
C6H5CH2COOH ⇌ C6H5CH2COO– + H+
In this equation, the acid (C6H5CH2COOH) dissociates into its conjugate base (C6H5CH2COO–) and a hydrogen ion (H+).
The equilibrium expression for this reaction is given by:
Ka = [C6H5CH2COO–] [H+] / [C6H5CH2COOH]
Where [C6H5CH2COO–], [H+], and [C6H5CH2COOH] represent the concentrations of the conjugate base, hydrogen ion, and the acid, respectively.
We are given that the initial concentration of phenylacetic acid is 0.021 M and the pH of the solution is 2.99. From the pH, we can determine the concentration of the hydrogen ion ([H+]) using the relation:
[H+] = 10^(-pH)
So, [H+] = 10^(-2.99)
Now, we need to find the concentration of the conjugate base ([C6H5CH2COO–]). For a weak acid like phenylacetic acid, the concentration of the acid (initial concentration) and the conjugate base ([C6H5CH2COO–]) at equilibrium will be approximately the same.
Therefore, we can assume [C6H5CH2COO–] ≈ [C6H5CH2COOH] = 0.021 M
Substituting the values into the equilibrium expression, we have:
Ka = (0.021)(10^(-2.99)) / 0.021
Now, we can calculate the Ka value.