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Harr: Clinical Chemistry Exam Practice Questions and Answers Which formula correctly describes the relationship between absorbance and %T ? A. A = 2 - log %T B. A = log 1/T C. A = -log T D. All of these options - ANSWER-D. All of these options D Absorbance is proportional to the inverse log ...

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Harr: Clinical Chemistry Exam Practice

Questions and Answers


Which formula correctly describes the relationship between absorbance and %T ?




A. A = 2 - log %T


B. A = log 1/T


C. A = -log T


D. All of these options - ANSWER✔✔-D. All of these options




D Absorbance is proportional to the inverse log of transmittance.


A = -log T = log 1/T


Multiplying the numerator and denominator


by 100 gives:


A = log (100/100 X T)


100 X T = %T,


substituting %T for 100 X T gives:


A = log 100/%T


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A = log 100 - log %T


A = 2.0 - log %T


For example, if %T = 10.0, then:


A = 2.0 - log 10.0


log 10.0 = 1.0


A = 2.0-1.0 = 1.0


A solution that has a transmittance of 1.0 %T would have an absorbance of:




A. 1.0


B. 2.0


C. 1%


D. 99% - ANSWER✔✔-B. 2.0




B


A = 2.0 - log %T


A = 2.0 - log 1.0


The log of 1.0 = 0


A = 2.0


In absorption spectrophotometry:

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A. Absorbance is directly proportional to


transmittance


B. Percent transmittance is directly proportional to concentration


C. Percent transmittance is directly proportional to the light path length


D. Absorbance is directly proportional to concentration - ANSWER✔✔-D. Absorbance is directly

proportional to concentration




D Beer's law states that A = a × b × c, where a is the absorptivity coefficient (a constant), b is the path

length, and c is concentration. Absorbance is directly proportional to both b and c. Doubling the path

length results in incident light contacting twice the number of molecules in solution. This causes

absorbance to double, the same effect as doubling the concentration of molecules.


Which wavelength would be absorbed strongly by a red-colored solution?




A. 450 nm


B. 585 nm


C. 600 nm


D. 650 nm - ANSWER✔✔-A. 450 nm




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A A solution transmits light corresponding in wavelength to its color, and usually absorbs light of

wavelengths complementary to its color. A red solution transmits light of 600-650 nm and strongly

absorbs 400-500 nm light.


A green-colored solution would show highest transmittance at:




A. 475 nm


B. 525 nm


C. 585 nm


D. 620 nm - ANSWER✔✔-B. 525 nm




B Green light consists of wavelengths from 500-550 nm. A green-colored solution with a transmittance

maximum of 525 nm and a 50-nm bandpass transmits light of 525 nm and absorbs light below 475 nm

and above 575 nm. A solution that is green would be quantitated using a wavelength that it absorbs

strongly, such as 450 nm.


SITUATION: A technologist is performing an enzyme assay at 340 nm using a visible-range

spectrophotometer. After setting the wavelength and adjusting the readout to zero %T with the light

path blocked, a cuvette with deionized water is inserted. With the light path fully open and the 100%T

control at maximum, the instrument readout will not rise above 90%T. What is the most appropriate first

course of action?




A. Replace the source lamp

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