Imagine that you are the quality control analyst supervising the synthesis of as

Question

Imagine that you are the quality control analyst supervising the synthesis of aspirin, HC_9H_7O_4, a monoprotic acid. One tablet is required to contain 325 mg of aspirin. To analyze your product, you dissolve one tablet In 290. ml H_2O, then titrate this solution with a 0.1000 M NaOH. You find that 17.49 mL of NaOH solution are required to reach the endpoint. How many mg of aspirin are actually in the tested sample tablet? mg Does this product pass your inspection? (To pass inspection the weight of the tablet must be within 0.5% the required weight.) Yes No

Explanation / Answer

Given molarity of NaOH = 0.1000 M

Volume of NaOH = 17.49 ml =0.01749 L

Volume of aspirin solution = 290 ml

Reaction equation of the aspirin with NaOH is as follows

HC9H7O4 + NaOH NaC9H7O4 + H2O

Lets first calculate moles of NaOH using the molarity and volume

Moles of NaOH = molarity * volume in liter

                            = 0.1000 mol per liter * 0.01749 L

                           = 0.001749 mol NaOH

Using the mole ratio of the NaOH and HC9H7O4 from the balanced reaction equation calculate moles of HC9H7O4

Mole ratio is 1 mol NaOH = 1 mol HC9H7O4

(0.001749 mol NaOH * 1 mol HC9H7O4) / 1 mol NaOH = 0.001749 mol HC9H7O4

We get the moles of HC9H7O4

Now lets convert moles of HC9H7O4 to its mass

Formula to calculate mass using moles is as follows

Mass in gram = moles* molar mass

Mass of HC9H7O4 = 0.001749 mol * 180.1574 g/mol

                                 = 0.315 g

We get mass in gram lets convert it to milligram

0.308 g * 1000 mg / 1 g = 315 mg

The actual amount of HC9H7O4 in the tablet is 315 mg.

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