Question

Consider a diprotic acid of unknown concentration. Suppose that you perform a titration and it required 36.12 mL of a standardized 0.250 M NaOH solution to titrate a 50 mL sample of the diprotic acid. What is the concentration of the unknown acid?

Answer 1

To find the concentration of the unknown diprotic acid, you multiply the volume of NaOH used by its molarity to get the moles of NaOH, then divide by 2 to get the moles of the acid, and finally divide by the volume of acid in liters. The concentration is found to be 0.0903 M.

Step-by-step explanation:

To determine the concentration of the unknown diprotic acid, we'll use the data from the titration with the standardized NaOH solution. Since a diprotic acid donates two protons (H+), the molar ratio of acid to NaOH is 1:2. First, calculate the moles of NaOH used in the titration:

# moles NaOH = (0.03612 L) × (0.250 M) = 0.00903 moles NaOH

Next, because the ratio is 1:2, there are half as many moles of the diprotic acid as NaOH, so:

# moles diprotic acid = 0.00903 moles NaOH / 2 = 0.004515 moles diprotic acid

Finally, calculate the concentration of the diprotic acid:

Molarity of diprotic acid = moles of acid/volume of acid in liters

Molarity of diprotic acid = 0.004515 moles / 0.050 L = 0.0903 M

The concentration of the unknown diprotic acid is 0.0903 M.