Question

What is the pH of a 0.53 M solution of formic acid? (Hint: The Ka of formic acid, HCOOH, is 1.8 x 10^−4.)

A) 1.74
B) 2.15
C) 2.64
D) 3.08

Answer 1

The pH of a 0.53 M solution of formic acid is 2.15.

Step-by-step explanation:

The pH of a solution can be calculated using the formula: pH = -log[H+]. In this case, the formic acid, HCOOH, is a weak acid and will undergo ionization in water according to the equation: HCOOH (aq) <=> H+(aq) + HCOO-(aq). The equilibrium constant for this reaction is known as the acid dissociation constant, Ka, which is given as 1.8 x 10^-4.

To calculate the pH of a 0.53 M solution of formic acid, we can assume that the concentration of H+ is equal to the concentration of formic acid that ionizes, x. Thus, the equation becomes: Ka = [H+] [HCOO-]/[HCOOH]. Plugging in the values, we have: 1.8 x 10^-4 = x^2 / 0.53. Solving for x, we find x = 0.0067 M.

Finally, we can calculate the pH using the formula: pH = -log (0.0067) = 2.17. Therefore, the correct answer is B) 2.15.