Question 1 1. In order to determine the amount of un-reacted salicylic acid (con

Question

Question 1

    1. In order to determine the amount of un-reacted salicylic acid (considered an impurity) present in your final product, a calibration curve is used. The curve will be made using several solutions of known but varying salicylic acid concentration (M). Using the following data, determine the molarities of the standard solutions as described in the accompanying table.

         Molar mass of salicylic acid : 138.12 g/mol

      Preparation of the stock solution of salicylic acid:

a.    0.200 g of salicylic acid was placed in a 250. mL beaker, 10.0 mL of 95% ethanol was added, and the solution was stirred until all solid had dissolved.

b.    150. mL of distilled water was added to the beaker and thoroughly mixed.

c.    The solution was quantitatively transferred to a 250. mL volumetric flask, and distilled water was added to the 250. mL mark. What is the precise molar concentration of this stock solution of salicylic acid?

Table I

Initial mass of salicylic acid (g)

Moles of salicylic acid (mol)

Initial molarity of salicylic acid (M) stock solution

Initial mass of salicylic acid (g)

Moles of salicylic acid (mol)

Initial molarity of salicylic acid (M) stock solution

Explanation / Answer

a)

initial mass, as stated, is 0.2 g of acid

b)

MW of salicylic acid = 138.121

moles of s.a. = mass/MW = 0.2/138.121 = 0.00144800 moles

c)

initial molarity then will be:

M = mol/V

Vfinal = 250+250 = 500 mL = 0.5 L

M = 0.00144800 / (0.500)

M = 0.002896 M of Salicylic acid initially as stock

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