Homework Help: Chemistry

Posted by Sharon on Tuesday, February 28, 2012 at 6:55pm.

Indicate how each of the following would affect the value of the absorbance (too high, too low, or not effect) of the indicated solution.
I really need help. I do not understand these questions!
This is from a chemistry activity to determine the unknown concentration of an Erythrosin B solution by using a spectrophotometer.

a. A student prepares solution A as instructed and pours it into a wet beaker.

b. A student rinses the 10.00 mL pipet only with DI water in the preparation of D (but does the rest of the procedure as instructed).

c. A student fills the volumetric flask containing solution B so that the bottom of the meniscus is below the mark on the flask (but does the rest of the procedure as instructed).

Chemistry - DrBob222, Tuesday, February 28, 2012 at 9:18pm
You haven't provided a clear set up but here is my best guess. I will put a proviso on each.
a. IF you are talking about the absorbance of soln A after it has been poured into a wet beaker, the absorbance will be less BECAUSE the solution has been diluted (with the water in the wet beaker).

b. Here it isn't clear what absorbance on what solution we're talking about but the solution of D will be weaker than your calculations show because the pipet delivered some sample diluted with water that was already in the pipet. With this information you should be able to take this weaker solution and follow through to the appropriate answer.

c. Again it isn't clear how solution B figures into the rest of the problem but you know that the sample in the volumetric flask will be more concentrated than calculations show it to be because less water was added to the volumetric flask.

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