Spectroscopic Determination of Iron with Phenanthroline

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Experiment A
Spectroscopic determination of Iron with Phenanthroline

Unknown # 2
Mass of Mohr’s Salt: 0.2040

1. 5mL of 6M acetic acid was measured and transferred into a 100mL volumetric flask with a pipette and diluted to the mark. Concentration= [0.2040(±0.0001)g/100(±0.08)mL]*[(1mol/392.16g)/(1L/1000mL)]

= 0.005202(±0.09382%)
= 0.005202(±0.000005)mol/L

2. 10mL of the above stock solution was transferred to a 250 mL volumetric flask and diluted to the mark. Concentration= [0.005202(±0.09382%)mol/L]*[10(±0.02)mL/250(±0.12mL)]
= 0.00020808(±0.22607%)
= 0.00020808(±0.0000005)mol/L

3. Standard error of burette is 0.02mL in every reading.
Solution| Desired Volume| Absorption 1| Absorption 2| Average Absorption| Standard 1| 30| 0.662| 0.664| 0.662|
Standard 2| 25| 0.544| 0.546| 0.545|
Standard 3| 20| 0.43| 0.434| 0.432|
Standard 4| 15| 0.317| 0.309| 0.313|
Standard 5| 10| 0.222| 0.217| 0.2195|
Standard 6| 5| 0.113| 0.112| 0.1125|
Unknown 1| | | | 0.096|
Unknown 2| | | | |

4. Sample standard concentration calculation with standard 1, Concentration= [30(±0.02)mL/100(±0.08)mL]*[0.00020808(±0.0000005)mol/L]
= 0.000062424(±0.2807%)
= 0.000062424(±0.0000002)

5. From the Calibration curve of Absorbance Vs Concentration, we know the equation of the graph is : y = 10553.63(±190.5558)x - 0.00363(±0.007721) Where, y is the absorbance and x is the concentration.
We know the absorbance of the unknown is 0.096. Therefore, 0.096 = 10553.63(±190.5558)x - 0.00363(±0.007721)
x= [0.096+0.00363(±0.007721)]/ [10553.63(±190.5558)]
= 0.00000944(±7.957%)
= 0.0000094(±0.0000008)

6.

Standard Concentrations| Uncertainties| Average Absorbencies| 0.000062424| 0.0000002| 0.662|
0.00005202| 0.00000013| 0.545|
0.000041616| 0.000000108| 0.432|
0.000031212| 0.00000007| 0.313|
0.000020808| 0.00000006| 0.2195|...
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