CHEMISTRY 133 – Spring, 2016

                                                                    Quiz 4 – KEY

 

1.      Which of the following can lead to apparent or real deviations from Beer’s law:

a) compounds have ground and excited energy states with a wide range of energies

b) very low concentrations                                c) use of very monochromatic light

d) compounds that can exist in an acid or base form

(2 pts)

 

2.  It is desired to measure compound X at 273 nm.  If a 0.0030 M solution of X gives an absorbance value of 0.581, what is the transmittance (T = P/Po)?  (4 pts)

A = -logT (rest of the information – e.g. l value and concentration are not needed)

T = 10-A = 10-0.581 = 0.262

 

3.   An interference filter is prepared to pass 400 nm light using “first order” (n = 1) light.  In order to avoid contamination of this light from higher order light (e.g. n = 2, n = 3, etc.), an additional filter is placed in the optical path.  Should this second filter remove lower or higher wavelength light?  Explain your answer.  (4 pts)

With an interference filter (see diagram below), nl = 2d.  For first order set to 400 nm, we know n = 1 and  = 400 nm. This means d = 400 nm/2 = 200 nm.  For other order light (n = 2, 3, etc.) l = 2d/n will be at LOWER wavelength (e.g. 2(200 nm)/2 = 200 nm for n = 2),  so we would want to remove light with l less than 400 nm.