A standard aspirin tablet in the United States contains 325 mg of acetylsalicyli

Question

A standard aspirin tablet in the United States contains 325 mg of acetylsalicylic acid (m = 180.15 g/mol). An important issue involving pharmaceuticals is their shelf life. If aspirin ta ts are left open to humid air, they absorb water from the air. One molecule of acetylsalicylic acid reacts with one molecule of water in a hydrolysis reaction that is first-order in each reactant. Suppose under extremely humid conditions, one aspirin tablet absorbs 1.15g of water. (a) Calculate the molar ratio of water to acetylsalicylic acid. Number (b) Is it valid to analyze the hydrolysis reaction of one aspirin tablet and this quantity of absorbed water using pseudo-first-order kinetics?

Explanation / Answer

a) The weight of one aspirin tablet = 325 mg =0.325 g

one tablet absorbs 1.15 g water

So, 0.325g absorbs 1.15 g water.

Then 180.15 g ( 1 mol) absorbs = (180.15 x 1.15) / 0.325 = 637.45 g water

moles of water = 637.45 g / 18g/mol = 35.41 mol of water

35.40 moles of water to 1 mole of acetyl salicylic acid

b) No.

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