Question

One method for determining the purity of aspirin (C9H8O4) is to hydrolyze it with NaOH
solution and then titrate the excess NaOH. The reaction of aspirin with NaOH is:
C9H8O4(s) + 2OH–(aq) → C7H5O3–(aq) + C2H3O2–(aq) + H2O(l)
A 1.487-g sample of impure aspirin was boiled in 50.00 mL of 0.500 M NaOH. After the
solution was cooled, it took 31.92 mL of 0.289 M HCl to titrate the excess NaOH.
Calculate the mass percent of aspirin in the original sample.

Answer 1

Please show your attempt on this problem.

Answer 2

I understand how to calculate mass percent when two values are present. To complete this problem I need to determine the amount dissolved so perhaps I use Ksp? I do not understand where to begin with this problem which is why there is none of my original work shown. I'm sure an ice or moles table is involved I just don't know where. Thanks in advance.

Answer 3

The moles of aspirin and moles of HCl are equal to the moles of NaOH:

\(\sf n_{NaOH}=n_{aspirin}+n_{HCl}\rightarrow n_{aspirin}=n_{NaOH}-n_{HCl}\)

Convert to mass:

\(\sf m_{aspirin}=n_{aspirin}*Mr_{aspirin}\) Mr=molar mass, btw

Using the formula for mass percent:

\(\sf mass ~percent~ of~ aspirin=\dfrac{ m_{aspirin}}{mass~of~sample}*100\%\)

Sub in everything:

\(\sf mass ~percent~ of~ aspirin=\dfrac{(n_{NaOH}-n_{HCl})*Mr_{aspirin}}{mass~of~sample}*100\%\)

Answer 4

In a titration, there is going to be a neutralization reaction, giving salt and water.

What you need to know is what amount of aspirin reacted with the NaOH, to give you the salt and water. And how many moles of HCl reacted with the remanent NaOH for the second reaction.

Look at your reaction again: how many moles of sodium hydroxide where consumed, and how many moles of aspirin?
Taking that into account you should be good to go.
Remember there are two reactions