This is a three part question. I would appreciate tremendously if all three part

Question

This is a three part question. I would appreciate tremendously if all three parts were answered, thank you. The questions are as follows:

a. Aspirin is a weak monoprotic acid. Calculate the volume of 0.493 M NaOH required to titrate a 0.1527-g sample of aspirin. (Pay attention to significant figures in your answer)

b. A student reached the end point of the titration in the previous question 0.34 mL before expected based on the volume calculated in Question a. What is the purity of the sample?

c. A student required more titrant than predicted as necessary in Question 2. Explain why this might occur.

Explanation / Answer

Ans. 1. Aspirin is a weak monoprotic acid, so 1 mol aspirin donates 1 mol H+ ions.

Molar mass of aspirin = 180.157 g mol-1

Mass of aspirin = 0.1527 g     ; [given]

Moles of aspirin in 0.1527 g sample = Mass/ molar mass

                                                = 0.1527 g / (180.157 g mol-1)

                                                = 8.476 x 10-4 moles

Stoichiometry: 1 moles of aspirin (monoprotic) is neutralized by 1 mol of NaOH. Therefore, at the end point of titration (or neutralization reaction)-

            Moles of aspirin = moles of NaOH

8.476 x 10-4 mol = Molarity of NaOH x volume (L) of NaOH solution

Or, 8.476 x 10-4 mol = 0.493 M x V

Or, 8.476 x 10-4 mol = (0.493 mol/ L) x V                   ; [Molarity, M = mol/ L]

Or, V = 8.476 x 10-4 mol / (0.493 mol/ L) = 0.0017192 L

            = 1.72 mL

Hence, required volume of NaOH = 1.72 mL

Ans. 2. Moles of aspirin = moles of NaOH

            Or, Moles of aspirin = 0.493 M x 0.00034 L = 0.00016762 moles

Hence, moles of aspirin in sample = 0.00016762 mol

Mass of aspirin = Moles x Molar mass = = 0.00016762 mol x (180.157 g mol-1) = 0.0302 g

Assuming 0.1527 g as the theoretical yield,

            % purity = (Aspirin obtained / theoretical yield) x 100

                        = (0.0302 g / 0.1527 g) x 100

                        = 19.76 %

Ans. 3. Requiring more titrant (NaOH) means that-

            I. The sample has greater % purity of aspirin because larger amount of aspirin in sample requires larger amount of NaOH for neutralization.

            II. The sample might be contaminated with traces of acid or the titrant might be contaminated traces of acid.

Since no background information is provided for the cause of increase in NaOH consumption, both the reasons may hold true.

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