[dinky]

I need to understand in english exactly what my group accomplished in a lab using the spec 20, a blank w/h2O, a calibration curve from cobalt standards, at 515 nm, and then analysising colas for phosphoric acid.  I understand just not in english!!!!  So I guess I really don't understand after all.  We used an AV for our reagent.  What (in english) are we accomplishing?  Or maybe what I'm asking is How?  I'm obviously confused.

thanks for any help.

[lemonoman]

Spectrophotemetry is the use of light to figure out how much of something is in something else.  In this case, the amount of phosphoric acid in cola.

You gave a lot of info, but not QUITE enough to determine exactly what's going on, but here...I'll take a guess  

Sounds like you're going to react the phosphoric acid with a cobalt compound...so the amount of cobalt is proportional to the amount of phosphoric acid.  Then, you'll have a set of standards (solutions with varying amounts of cobalt in them).  Obviously, if the solutions have similar amounts of cobalt in them (and nothing else) then they will be the same colour.  That's what Spec is (at visible wavelengths, anyways, like 515 nm).  It'll measure the colour of the standards, and the colour of the cola after you reacted it...and then with a little math you can figure out exactly how much acid was in the cola.

The 'standards' thing is just to account for other stuff in your sample.  Like, if you used NaCl at some point (which you probably won't, but this is an example)...then it's going to change the colout EVER so slightly.  Using standard accounts for this, because the colour change is, well...accounted for.

P.S. Using the word 'colour' here is an oversimplification.  REALLY, Spec-20s (a generic spectrophotometer - cheap, and that why it's in schools )...they measure the transmittance of light...so some of the light is blocked, some of it gets through...and how much gets through is what the reading is. It can be done at any wavelength, but certain wavelengths are best for certain compounds - like around 515 for cobalt, I assume.

Good luck.