Chemistry Investigation Help

I am doing a chemistry investigation on the determination of paracetamol content in painkillers and I used the instructions on the RSC publication on paracetamol, and I followed them exactly as follows:

Procedure as outlined in the British Pharmacopoeia 1988
Safety
Wear eye protection.
Paracetamol formulations – do not ingest.
Sulfuric acid (1 mol dm–3) – corrosive, especially when hot.
Hydrochloric acid (2 mol dm–3) – irritant.
Ferroin solution – hazards unknown. May cause skin irritation.
Ammonium cerium(IV) sulfate – respiratory tract irritant, strong oxidising agent, keep
away from flammable material.
1. Dissolve 0.3 g of a mixture containing paracetamol in a mixture of water (10 cm3)
and 1 mol dm–3 sulfuric acid (30 cm3).
2. Boil under reflux for 1 hour, cool and dilute with water (100 cm3).
3. To 20 cm3 of the resulting solution add cold water (40 cm3, 2 mol dm–3
hydrochloric acid (15 cm3) and ferroin solution (0.1 cm3, 0.1 wt% or
0.025 mol dm–3).
4. Titrate with 0.1 mol dm–3 ammonium cerium(IV) sulfate (VS – volumetric standard)
until a yellow colour is produced.
5. Repeat the operation without the test material being present. The difference
between the titration figures represents the amount of ammonium cerium(IV) sulfate
required. Each cm3 of 0.1 mol dm–3 ammonium cerium(IV) sulfate is equivalent to
0.007560 g of paracetamol.
This method can be used to analyse the quantity of paracetamol present in many
medicines that contain the drug.

The first time I did this I got a colour change from red to yellow but now when i do it there is no colour change, it just becomes pink instead of going yellow and i dont know why.

Any suggestions would be greatly appreciated

Thanks :smile:

Reply 1

FTC199

maybe some of your chemicals have gone off? i know they can do that if left for a while

Reply 2

Fluorine

i tried it again, and i got more ammonium cerium (IV) sulphate made up and it does look like a different colour.

but i think it was that i didnt have enough ferroin indicator in it.

it's working now

thanks :smile:

FTC199

maybe some of your chemicals have gone off? i know they can do that if left for a while

Reply 3

zwitterion

i did an experiment testing the decomposition of hydrogen peroxide by different potassium compounds. Only potassium iodide worked (catalysed decomposition of h202) but potassium chloride and potassium bromide never worked. Why?