Solution of formic acid (HCOOH) with a pH of 1.98. Find the molarity of the acid.
........HCOOH ==> H^+ + HCOO^-
I.........M.......0......0
C........-x.......x......x
E........M-x......x......x
The problem tells you the pH is 1.98. Use pH = -log(H^+) to find x. Then substitute into Ka expression for HCOOH (you will need to look up Ka for HCOOH) and solve for M.
To find the molarity of the formic acid solution, we need to use the relationship between pH and concentration. The pH of a solution is related to the concentration of hydronium ions (H3O+) present in the solution.
The pH scale is logarithmic, meaning that each unit change in pH represents a tenfold change in concentration of H3O+ ions. The relationship between pH and concentration can be described by the equation:
pH = -log[H3O+]
To find the concentration of H3O+ ions, we rearrange the equation:
[H3O+] = 10^(-pH)
Given that the pH of the formic acid solution is 1.98, we can find the concentration of H3O+ ions:
[H3O+] = 10^(-1.98)
Calculating this value, we find that [H3O+] = 0.01122 M (to four significant figures).
Since formic acid (HCOOH) is a weak acid, it partially dissociates in water. However, for dilute solutions, we can assume that the concentration of formic acid is approximately equal to the concentration of H3O+ ions. Therefore, the molarity of the formic acid is approximately 0.01122 M.