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    this may sound dumb but i have no idea how to use a Spectrophotometer. I want to use beers law to calculate the concentration of a substance. I need to calculate the molar extinction co-efficient, but i need a concentration before i can find that. It says to use a substance of "known concentration", get the molar extinction co-efficient and then use the "unknown concentration" sample to find the concentration. If that makes sense.

    What is the known concentration though? a standard solution? can it be any standard solution?

    it talks about graphs too, what graphs should i draw and what do i do with them?

    please help me!

    say that my "unknown" is a mixture of ammonia and copper, could i use a sample of ammonia as the standard solution?


    :confused: :confused:

    I did this with distilled water and stock dye and when I calibrated it i used the distilled water. In this I'm going to assume that you calibrate it with a sample of ammonia that has 0% copper in it. That way you get the initial starting point for your graph

    For your graph , you could do an absorbance v concentration grah

    your x axis is going to be the concentration of copper (this is the variable you control - so you'll be changing the conc of copper) and your y axis will be the absorbace at whatever nm (e.g. 520nm).

    So you plot all your values according to what your readings are on the spec at different concs, and then draw a line of best fit. Now you have that unknown solution - run that through your spec and see what absorbance reading you get. you can apply this to the info your graph and line of best fit gives you.

    Hope that helps
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