Aspirin

1.

Equation: NaOH + HCl(aq) --> NaCl + H2O

2.

Work out titre value of NaOH (I think it was 27.35cm^3) and divide it by 1000 to get it in dm^3

3.

Work out number of moles by multiplying the volume by the concentration.

4.

1:1 ratio with hydrochloric acid gives you the number of moles of hydrochloric acid in 25cm^3.

5.

Scale up to 250cm^3 by multiplying by 10 to get the actual number of moles that was excess.

6.

You use the concentration and volume of hydrochloric given in the FIRST part of the answer to work out the number of moles of excess hydrochloric acid there was to begin with.

7.

You then do (number of moles of hydrochloric acid at the beginning)-(number of moles that reacted with NaOH)

8.

This gives you the number of moles that reacted with aspirin.

9.

The question (I think) said it was a 1:1 ratio so the number of moles of hydrochloric acid was the same for aspirin.

10.

Work out the Mr which was 180 and work out mass by multiplying moles by 180. I got 0.954g.

11.

This is the mass in GRAMS in THREE tablets.

12.

So you multiply by 1000 to get it in mg which is 954mg and divide it by 3 to get the mass of one tablet which I got was 318mg.