AAMC 7R: PS Question #28 - Absorbance

[SailCrazy]

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The answer in the solutions isn't actually about this question at all, so I have no clue what I did wrong... 🙁

The question asks:
"The molar absorptivity of bromine at 395 nm is 198M-1 cm-1. What is the absorbance at 395 nm in Experiment 1?"

In the passage they gave the equation A = Ecl
Absorbance = (absorbtivity constant) (concentration) (Length normally 1.00 cm)

I simply took the 198 given in the question times the 4.14e-3 listed for [Br2] in experiment 1 time 1cm

So...
(198) * (4.14e-3) * (1)
or approximately: 2e2 * 4e-3 = 8e-1
= 0.8 which is choice B. However, the key says that C (1.22) is correct. 😕

Any help?

 

[Medikit]

The answer in the solutions isn't actually about this question at all, so I have no clue what I did wrong... 🙁

The question asks:
"The molar absorptivity of bromine at 395 nm is 198M-1 cm-1. What is the absorbance at 395 nm in Experiment 1?"

In the passage they gave the equation A = Ecl
Absorbance = (absorbtivity constant) (concentration) (Length normally 1.00 cm)

I simply took the 198 given in the question times the 4.14e-3 listed for [Br2] in experiment 1 time 1cm

So...
(198) * (4.14e-3) * (1)
or approximately: 2e2 * 4e-3 = 8e-1
= 0.8 which is choice B. However, the key says that C (1.22) is correct. 😕

Any help?

My guess is that the pathlength in the experiment is actually 1.5 cm.

 

[SailCrazy]

I wondered about that too, but I don't see any information on path length given anywhere, other than the statment that is is normally 1.00 cm... 😕

My guess is that the pathlength in the experiment is actually 1.5 cm.

 

[Medikit]

I wondered about that too, but I don't see any information on path length given anywhere, other than the statment that is is normally 1.00 cm... 😕

Yeah, I think they messed up, is this 7 or 7R?

 

[SailCrazy]

7R

Yeah, I think they messed up, is this 7 or 7R?

 

[Medikit]

7R

Yeah that's pretty strange. I would just move on, you're doing everything right.

 

[aamartin81]

Yeah that's pretty strange. I would just move on, you're doing everything right.

I took practice test 7 today, entered B for #28 and it was graded correctly online.

Adam

 

[SailCrazy]

HHmmm, That would help to make sense of things.

I did print out the key, and I double checked it. I'll simpy accept that I have the right answer and move on then! 😎

Thanks, that makes my day - it might even give me another point on my overall score! 😀

I took practice test 7 today, entered B for #28 and it was graded correctly online.

Adam