[shahirahzulfah]

Hye all...
i got prob with methyl salicylate assay..
im not sure whether i understand the procedure..
but everytime i did the analysis.. i didnt get the result..
so i have to do GC analysis to get the assay rather than do it by titration..

here is the procedure for methyl salicylate assay by titration

1.Dsolve 0.500 g in 25 ml of alcohol  R.
2.Add 0.05 ml of phenol red solution R and neutralise with 0.1M sodium hydroxide.
3.To the neutralised solution add 50.0 ml of 0.1M sodium hydroxide and heat under a reflux condenser on a water-bath for 30 min.
4.Cool and titrate with 0.1M hydrochloric acid.
5.Calculate the volume of 0.1M sodium hydroxide used in the saponification.
6.Carry out a blank titration.

1 ml of 0.1M sodium hydroxide is equivalent to 15.21 mg of C8H8O3.

i really want to know what does it mean by Add 0.05 ml of phenol red solution R and neutralise with 0.1M sodium hydroxide
coz when i add with phenol red solution the colur of solution became red. when it says neutralised with sodium hydroxide does it mean i have to add with NaOH untill the colur become deep pink?

reallt need your attention... thanx all

[Borek]

What is initial color of the solution? According to tables (see for example http://www.ph-meter.info/pH-measurements-indicators) phenol read changes color in the 6.4-8.2 range from yellow to red. I suppose you start with red solution - and you have to neutralize it down to around 7, so you should end with the yellow one. Prepare two identical solutions of your sample, add phenol red to both, add excess NaOH to one, this way you will have two solutions to prepare your sample to.