Extinction and concentration

[HansLaroes]

Hello,

For a Chemistry project i have to determine the starch concentration of two solutions of which i only know the extinction (which i had of course determined using a colorimeter) using a calibration line plotted in excel derived from samples  of which the concentration + extinction was known. The problem is that i forgot to note the molarity of the starch-solution - from which i derived my samples -, even though i did note the mass concentration in g/L. Therefore i made a graph in excel with the concentration is in g/L and the extinction. Is this a valid relation? Or do i need to know the molarity of the starch-solution?

Best regards,

Hans

[studiot]

Well since

[math]molarconcentration = \frac{{massconcentration}}{{molecularmass}}[/math]

and the molecular mass is a constant the form of your graph is OK,

but obviously for any result that needs to involve the the molar mass you will need that constant.

[HansLaroes]

Thank you, very much!

[BabcockHall]

Unless the starch molecule has a defined number of glucose monomers, I don't see how it can have a single molecular weight.  Polymers are not my strongest suit, but it might be possible to define an average molecular weight.

[studiot]

2 hours ago, BabcockHall said:

Unless the starch molecule has a defined number of glucose monomers, I don't see how it can have a single molecular weight.  Polymers are not my strongest suit, but it might be possible to define an average molecular weight.

I presume there is a particular starch involved.

This may be for a pharmacy course and pharmacists often use average molecular weights.

And 'starch' is a common constituent of pills various.