[odicon]

100 ml of a solution contains 0.050 g of a coloured compound that absorbs exactly half the incident light intensity at 500 nm when the solution is in a 1.00 cm wide spectrophotometer cell. The cell width that would absorb 75% of the incident light intensity is:

a. 0.5 cm
b. 1.0 cm
c. 2.0 cm
d. 4.0 cm
e. (log 10 2) cm
f. none of the above


The mass of the coloured compound in the same solution as in question 1 above that would have an absorbance of 1.5 in the same 1.00 cm cell is (in grams):

a. 0.050
b. 0.075 log10 2
c. 0.033 log10 2
d. 0.075 / log10 2
e. 0.075 / log10 0.5
f. none of the above

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For the first question, I used A = log (I_o/I) = E c l  where E c is constant and solved for l. I got 2.0cm. Do you think that is correct?

for the second question, I do not have much idea on how to approach it.
how would you rearrange the equation?

Help would be appreciated. Thanks. 

[Dan]

For the first question, I used A = log (I_o/I) = E c l  where E c is constant and solved for l. I got 2.0cm. Do you think that is correct?

Agreed, I got 2.0 cm as well

for the second question, I do not have much idea on how to approach it.
how would you rearrange the equation?

Play the same game, but this time El is constant rather than Ec. You can simplify further and substiture for c = Bm (mass x another constant)

so, A = Ecl = ElBm = Dm (where D = ElB is a constant, m is mass)

Now that everything is expressed in terms of absorbance, mass and a constant it is easier to solve for the unknown mass

[odicon]

Thanks a lot Dan!
So do you know what to plug in for the value B? (or D)?

[odicon]

oops never mind. I see what you mean. Thanks.

[bbrar1]

Hey so I still do not understand what it means to set something to a constant. c is concentration in moles/litre, but we are not given moles so how do I find the concentration? Also, what would I set Io and I to? Absorption is .50 if I understand correctly, but I have no idea what the other values are!! Please Help