Question

A 20.00-ml sample of a weak monoprotic acid is titrated with 0.0603 m naoh. at the endpoint, it is found that 43.98 ml of titrant was used. what was the concentration of the weak acid?

A. 0.0274m
B. 2.65m
C. 6.86e⁻⁵ m
D. 0.133m
E. 0.0603m

Answer 1

Using the provided volumes and molarities of NaOH and the sample acid, the moles of NaOH at equivalence are calculated and found equal to the moles of the weak acid. The concentration of the weak acid is then determined by dividing its moles by its volume in liters, resulting in a concentration of 0.132567 M.

Step-by-step explanation:

To calculate the concentration of the weak acid in a titration experiment, we use the principle that at the equivalence point, the moles of the titrant (NaOH) added are equal to the moles of the weak acid present in the solution. The molarity (M) is the number of moles of a substance per liter of solution, therefore by using the volume and molarity of the titrant (NaOH) and the volume of the acid solution, we can determine the molarity of the weak acid.

In the given problem, 43.98 mL of 0.0603 M NaOH was used to titrate a 20.00-mL sample of the weak monoprotic acid. The number of moles of NaOH used is calculated as follows:

Moles of NaOH = Molarity of NaOH × Volume of NaOH in liters

Moles of NaOH = 0.0603 M × 0.04398 L = 0.00265134 moles

Since the acid is monoprotic and at equivalence point, the moles of acid will be equal to moles of NaOH.

Moles of weak acid = Moles of NaOH = 0.00265134 moles

Now, we will find the concentration of the weak acid:

Concentration of weak acid = Moles of acid / Volume of acid in liters

Concentration of weak acid = 0.00265134 moles / 0.02000 L = 0.132567 M