A2 Chemistry
Read our general notes on Risk Assessment
I plan to calculate the percentage composition of lab-synthesised aspirin using interpolation (the suggested method on this site), and I have performed the required titrations (eg. for salicylic acid, ASA, and my sample). Can you suggest a step-by-step method to interpolation, or any relevant sites that describe this process? Thanks a lot, this site is very much appreciated by all of my fellow students on the Salters' course.
Igloo writes ...
First you might like to take a look at this web reference which I found today:
http://www.ic.sunysb.edu/Class/che134/susb/susb012.pdf
It’s fairly high-powered, but do read it carefully and see whether you understand what it’s all about. You should concentrate on the section to do with “indicator titration”. It seems to me that the author is making rather heavy weather of everything, introducing the concept of EMM (effective molar mass), but you may think that this concept is worth exploring in order to impress your teacher!
To answer your question in very simple terms, do the following.
1 Set up two vertical axes, one on the left-hand side of the page, the other on the right, and draw a horizontal line between them at the base of the vertical lines.
2 The vertical axes represent titration readings (both sides can be labelled in the same way)
3 The horizontal axis is labelled “composition”. On the left you could have 100% ASA (0% SA), and on the right 100% SA (0% ASA). Mark off the horizontal axis with percentage values from 0-100% SA.
4 Mark your two titration readings for the pure substances on the left and right-hand axes, respectively, and draw a straight line between these points.
5 Read off on the horizontal axis the value of your titration for the mixture, and you have determined the composition of your mixture.
6 I think at this stage you need to think for yourself, e.g. about what these percentage values represent. Is this a composition by mass? If so you may want to convert this to a molar composition. At this stage you may find the article helpful!!
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
Rate this page or react
Share your views on this page, 5 ratings so far
, rated at 
updated: 12 February 2007
