[ridic]

An aqueous stock solution (“S”) containing 8.657 mg of gallium (Ga) per mL of solution is diluted in the following manner. A 3.00 mL aliquot of this solution is added to a 150.00 mL volumetric flask. Upon addition of the proper reagents, gallium is known to form an aqueous Ga+3-complex that contains one (1) Ga+3 cation per complex formed. [This complex has a maximum absorbance at 393 nm.] Next, sufficient deionized water is then added to the volumetric flask (and contents) so that the final solution volume is 150.00 mL. This is solution “X”. A 3.00 mL aliquot of solution “X” is added to a clean, empty 150.00 mL volumetric flask. Sufficient deionized water is then added so that the final solution
volume is 150.00 mL. This is solution “Y”.

1. Determine the concentration (in M) of Ga in Solution S and determine the concentration (in M) of Ga+3(aq) in solution X and in solution Y.

2. Solution Y is placed in a tube of 1.00 cm path length and its %T is measured in the
Spec 20 set at 393 nm. The percent transmittance is found to be 47.65 %. Determine the absorbance of solution Y and the molar extinction coefficient of the aqueous Ga+3-complex. Finally, calculate what the percent transmittance of solution X would be if it were measured with the same instrument in an identical tube of the same path length.

3. Explain why solution X was diluted (to make solution Y) and the %T of
solution Y - not of solution X - was actually measured.

[MrOHBrown]

I can't help you as it's been years since I've done spec...

BUT simply retyping your questions without demonstrating what you do know, or some method by which you have tried to approach the problem, is pretty lazy don't you think? Do some research, show us what you do know, give us a foundation from which to assist you as I doubt anyone here is keen to completely answer questions you appear to have made no attempt to answer yourself.

GO: Look up what a molar extinction coefficient is, find links about Gallium spectroscopy, don't expect US to answer it for you.

But I will give some ideas regarding part 3... Gallium transmittance might prove unreliable at higher concentrations and will require dilution. Diluting directly to solution Y, the one that can actually be analysed, would require taking a very tiny, and difficult to accurately measure, volume of the original gallium solution. Making solution X enables a much easier preparation of solution Y. Just a guess, after all, the last time I did spec was 8 yrs ago.

EDIT: Oh and if you can't determine the concentration of the solutions I wonder what on Earth you've been doing in your chemistry classes!!

Concentration = moles / Volume (in litres), Then use your dilution equations to determine concentrations for X and Y (C1 x V1 = C2 x V2)

[ARGOS++]

Dear Ridic;

Can you show us some of your calculations you did?  -   
And please read:  "Forum Rules” (4.)

The calculations for Question Nr.1 should be easy for you.

For Nr. 2  & 3 you must use the “Beer-Lambert Law”!
Take the following page as Hint and Explanation:  "Corrected Beer's Law”.
You have to translate the “Transmittance” into “Absorptions”, because Transmittance is not linear in Concentration.

With this help you should be able to solve all you Questions.
But show us at least some work, that we are able to help you.

Good Luck!
                    ARGOS⁺⁺