The K_a for formic acid is 1.8 × 10^-4. Which of the following statements best describes the pH of a 0.0010 M solution of formic acid? A)The pH is greater than 0 but less than 3. B)The pH is exactly 3. C)The pH is greater than 3 but less than 7. D)The pH is exactly 7. E)The pH is greater than 7 but less than 11.

Question

Quizplus · Accepted Answer

The pKa of formic acid is 3.75, which is between 0 and 7, indicating that it is a weak acid. A 0.0010 M solution of formic acid is a dilute solution, which means that it will not fully dissociate. Using the formula pH = pKa + log([A-]/[HA]), we can calculate the pH of the solution. Here, [HA] = 0.0010 M and [A-] = x (let's assume that x is the concentration of formate ions produced by the dissociation of formic acid). We can plug these values into the formula and solve for x:

3.75 = -log(1.8 × 10^-4) + log(x/0.0010)

x/0.0010 = 10^(3.75 + 4)

x = 8.9 × 10^-2 M

Now we can plug this value into the formula for pH:

pH = 3.75 + log(8.9 × 10^-2/0.0010)

pH = 3.08

Therefore, the best choice is C, as the pH is greater than 3 but less than 7, with a value of approximately 3.08.

The Ka for Formic Acid Is 1

The K_a for Formic Acid Is 1