(20 points) I have constructed a simple photometer consisting of only a flashlig
ID: 578916 • Letter: #
Question
(20 points) I have constructed a simple photometer consisting of only a flashlight, a simple interference filter that transmits light at 550 nm, a silicon photodiode, and a handheld multimeter. Shining the flashlight first through the filter and then through a 1.25 cm pathlength cuvette filled with an aqueous solution containing 543 g/L of compound Q (825.143 g/mol), I measure a voltage of 0.752 V on the multimeter. Replacing the sample with the blank, a voltage of 1.067 V was measured. Determine the following: 10. What is the transmittance of the sample of Q? What is the absorbance of the sample of Q? What is the molar absorptivity of compound Q? a. b. c. d. Now, let's use this previous sample of Q as a standard to determine the concentration of an unknown aqueous sample of compound Q (Unknown Q). A 99.00 mL aliquot of Unknown Q was combined with 1.00 mL of deionized water and photometric measurement gave an absorbance of 0.194. A second 99.00 mL aliquot of Unknown Ca was combined with 1.00 mL of the standard and photometric analysis gave an absorbance of 0.333. What is the concentration of Unknown Q in units of mol/L?Explanation / Answer
Transmittance= P/Po
P= Radiant power transmitted
Po= Radiant power incident on light
Power= V2/R.
where V is the voltage and R is the resistance of multimeter(constant)
a)
Therefore transmittance,T= (V/Vo)2 = (0.752/1.067)2
= 0.4967
b)
Absorbance, A= log(1/T)
=0.3039
c)
A=eCl
C= concentration=543*10-6/825.143
=6.58*10-7 M
l= path length=1.25 cm
e= molar absoptivity =A/Cl=0.3039/6.58*10-7*1.25
=3.69*10-6 M-1cm-1
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