When answering the problems make sure to in the space provided. Credits will be

Question

When answering the problems make sure to in the space provided. Credits will be given for setting up problems and using the correct approach to solve the problem. Answer all the questions (5 points for each correct answer) 1) After obtaining calibration curve for your known solution to have slope of 1.5 and intercept of 0.01, you determine that your unknown has Absorbance of 0.2. Is it enough to determine the concentration of your unknown and how? Demonstrate. 2) You used 2ml of your stock solution to make 1L of 0.3 mM of your final solution. What was the concentration of your stock solution? 3) If you measure Absorbance of 1 M solution in with cross-section areas of 4cm^2 and 9 cm^2., would you expect to see the same A and why? Demonstrate 4) Define void volume (V_0) in a gel permeation chromatography column?

Explanation / Answer

1. The calibration curve is drawn by taking absorption of the known concentrations of the same sample and the intercept is coming from the solvent or instrument parameters. If the experiment is performed under similar condition and the corresponding concentration for unknown can be obtained from the curve, which is a linear one. Since the absorbance Vs concentration curve is a linear one, one can easily plot the corresponding calibration curve by knowing the slope and y-intercept.

Given absorbance of the unknown is 0.2

y-intercept is 0.01

slope is 1.5

dy/dx =1.5

at y-intercept concentration of sample is zero and absorbance is 0.01

thus 1.5= (0.2-0.01)/dx

or dx= 0.1266 units

since the initial point is zero

dx is the concentration of the unknown

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