3. Acetylsalicylic acid (C9H8O4) is a weak monoprotic acid, commonly known as ‘a

Question

3. Acetylsalicylic acid (C9H8O4) is a weak monoprotic acid, commonly known as ‘aspirin’. The acetylsalicylic acid in an aspirin tablet is titrated using 0.1035 M NaOH, requiring 26.12 mL of the NaOH solution to reach the endpoint. Determine the mass of acetylsalicylic acid present in the aspirin tablet. (3 pts)

4. The concentration of SO2 in atmospheric samples can be determined by bubbling a sample of air through a trap containing H2O2. Oxidation of SO2 by H2O2 results in the formation of H2SO4. The amount of H2SO4 formed can be determined by titration with a standard NaOH solution. In a typical analysis, a sample of air was passed through the H2O2 trap at a rate of 1.25 L/min for a period of 60 minutes. The resulting solution required 23.76 mL of 0.0147 M NaOH solution to reach the phenolphthalein end point for the titration of the H2SO4. The density of SO2 at the temperature of the air sample is 2.86 mg/mL. Calculate the concentration of SO2 in the air sample in L SO2/L air. (4 pts)

Explanation / Answer

Ans 3 :

The reaction is given as :

C9H8O4 + NaOH = C9H7O4Na + H2O

The reaction shows an equimolar amounts of acid and NaOH used in the reaction.

Number of moles of NaOH = molarity x volume (in L)

= 0.1035 x 0.02612

= 0.00270342 mol

So number of moles of acetylsalicylic acid will also be 0.00270342 mol

Mass of acid = number of mol x molar mass

= 0.00270342 x 180.157

= 0.487 grams

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