What is the pH of a 0.001 M formic acid solution? Ka = 1.8 x 10^-4.
I don't know what to do!
To calculate the pH of a solution of formic acid, we need to calculate the concentration of H+ ions in the solution. This can be done using the equation for the ionization of formic acid:
HCOOH ⇌ H+ + HCOO-
The equilibrium constant for this reaction is given by the Ka value, which in this case is 1.8 x 10^-4. The equation for the Ka expression is:
Ka = [H+][HCOO-] / [HCOOH]
Since the concentration of formic acid (HCOOH) is 0.001 M, we can assume that the concentration of H+ (or [H+]) is also equal to 0.001 M initially.
Now, let's calculate the concentration of HCOO-. Rearranging the equation for Ka, we have:
[HCOO-] = (Ka * [HCOOH]) / [H+]
Plugging in the given values:
[HCOO-] = (1.8 x 10^-4 * 0.001 M) / 0.001 M
[HCOO-] = 1.8 x 10^-4 M
Now that we have the concentration of H+ and HCOO-, we can use the equation for pH:
pH = -log[H+]
In this case, [H+] = 0.001 M, so:
pH = -log(0.001)
pH = 3
Therefore, the pH of a 0.001 M formic acid solution is 3.
To find the pH of a solution, we need to calculate the concentration of hydrogen ions (H+) in the solution. In this case, we have a weak acid, formic acid (HCOOH), and we can use the value of Ka (acid dissociation constant) to find the concentration of H+.
The Ka value for formic acid is given as 1.8 x 10^-4. The Ka expression for formic acid is:
Ka = [H+][HCOO-] / [HCOOH]
Since formic acid is a monoprotic acid, the concentration of H+ is equal to the concentration of HCOO-. Therefore, we can assume [H+] = [HCOO-] = x (let's assign this value as x).
Substituting the values in the Ka expression:
1.8 x 10^-4 = x^2 / (0.001 - x)
Now, we need to solve this quadratic equation to find the value of x. To do this, we can use the quadratic formula:
x = [-b ± √(b^2 - 4ac)] / 2a
Considering that a = 1, b = 0, and c = -1.8 x 10^-7 (by rearranging the equation), we can simplify the quadratic formula to:
x = √(4ac) / 2a
x = √(4 * 1 * 1.8 x 10^-7) / 2 * 1
x = 6 x 10^-4
Therefore, the concentration of H+ is 6 x 10^-4 M. Now, to find the pH, we can take the negative logarithm (base 10) of the H+ concentration:
pH = -log[H+]
pH = -log(6 x 10^-4)
pH ≈ 3.22
So, the pH of a 0.001 M formic acid solution is approximately 3.22.