[diamorph]

here again to embarass myself some more..

"a sample has been prep. (from previously prep'd NO3 solutions) like this: 25mL diluted to 250mL (1), 10 of it - to 500mL. last one ran thru spectrophotometer giving an absorbance at 0.544.

calc. the concentr. of NO3 in the undiluted sample."

can't assemble the puzzle here, anyone care to explain some simple chemistry to me?

[JGK]

Were you provided with a molar extinction coefficient?

If so you use this together with the absorbance to calculate the concentration of the diluted sample.

Then work through the dilution process to calculate the original concentration.

[diamorph]

nope. molar absorptivity is not mentioned.
can you throw in a formula for it?

[diamorph]

also:

"potassium hydrogen phthalate is used as a primary standard for the standardization of an app. 0.10 M NaOH.

mass KHC8H4O4   mL NaOH
0.4171                 20.22
0.4089                 19.90
0.4302                 20.91

molarity of NaOH solution?"

the million dollar question - what do they refer to when they say "standardization"?

[JGK]

nope. molar absorptivity is not mentioned.
can you throw in a formula for it?

http://en.wikipedia.org/wiki/Beer-Lambert_law

[Borek]

the million dollar question - what do they refer to when they say "standardization"?

Determination of the exact concentration of the NaOH solution.

You owe me one.

One million, that is.