Rates of reaction - kinetics (A2)
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For my advanced higher chemistry investigation I am trying to determine how much aspirin is in aspirin tablets by two different methods. One is colorimetry. I am using a colorimeter that reads absorbance but I need to know how to change this into percentage transmission as my calibration graph is of percentage transmission against mass of aspirin rather than absorbance.
Igloo writes
Transmission is a measure of how much light of the chosen frequency actually passes through the solution, whereas absorbance measures how much has been removed or absorbed. Although these ideas are reciprocal, rather like frequency and wavelength, the relationship happens to be a logarithmic one:
A = 2 – log10(T)
where A is absorbance and T is percentage transmission.
Rearranged, since you need to have T as the subject of the formula, this becomes:
T = inverse log of (2 – A) [use the 10x or shift log button on your calculator]
For example, an absorbance of 0 gives a percentage transmission of 100, as you would expect, an absorbance of 1 gives a percentage transmission of 10% and an absorbance of 2 gives a percentage transmission of 1%. I suggest that you check these out with your calculator.
Perhaps it would be helpful to look at a suitable web reference if you wish to have more details about the concepts of transmission and absorbance. Use www.google.co.uk with, for example, “absorbance transmission” as your search phrase.
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updated: 18 December 2006
