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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: horsebox on January 25, 2010, 05:47:43 PM

Title: Job's Method
Post by: horsebox on January 25, 2010, 05:47:43 PM

I'm having trouble finding info on Jobs method of continuous variation because entering the word job into google yields results about jobs crazily enough.

So what I think I know about Jobs method is that it is a method of determining the stoichiometry of a reaction by preparing a series of solutions with varying concentrations of each reactant but the combined number of moles of reactants being equal among every solution. What I don't understand is the spectrophotometry part. Using the binding of Cu2+ ions to EDTA ligands as an example from what I read the concentration of the product (Cu/EDTA complex) is then determined using a spectrophotometer. I can see that the maximum amount of product will be formed in the solution whos mole fraction is closest to the actual stoichiometric ratio but wouldn't the unreacted Cu2+ and EDTA in all the other solutions influence the absorbance recorded by the spectrophotometer?

Title: Re: Job's Method
Post by: Borek on January 26, 2010, 02:14:12 AM

http://lmgtfy.com/?q=Jobs+method+of+continuous+variation

1. You can try to select wavelength at which only complex absorbs.

2. Even if that's impossible it only means that math is a little bit more complicated.

Title: Re: Job's Method
Post by: JGK on January 27, 2010, 02:15:56 PM

You will have much success if you google Job's method of continuous variation