Table1) Concentrations and Absorbance of Working Standards of Iron
|
Standard Solution #
|
Volume of Iron stock solution (mL)
|
Final Concentration of Iron (M)
|
Absorbance at
511 nm
|
|
1
|
0 mL
|
0
|
0.00
|
|
2
|
1 mL
|
5.13 x 10-6
|
0.066
|
|
3
|
3 mL
|
1.54 x 10-5
|
0.182
|
|
4
|
5 mL
|
2.57 x 10-5
|
0.325
|
|
5
|
10 mL
|
5.12 x 10-5
|
0.622
|
2.567 x 10-4 x 1 ml = 50 ml x X x = 5.13 x 10-6
2.567 x 10-4 x 3 ml = 50 ml x X x = 1.54 x 10-5
2.567 x 10-4 x 5 ml = 50 ml x Xx = 2.57 x 10-5
2.567 x 10-4 x 10 ml = 50 ml x X x = 5.12 x 10-5
|
Equation of the Trend line
|
R² Value
|
|
y = 12172x + 0.0018
|
R² = 0.9992
|
* Unknown Solution's Absorbance at 0.500 nm
0.500 = 12172 x + 0.0018
X = 4.093 x 10 -5mole/L
[ m1v1= m2v2]
X x 25 ml = 4.093 x 10-5mole/Lx 100ml
X = 1.636 x 10-4 mole/L (Original concentration)
(Molarity of mass of Fe = 55.85 g)
1.636 x 10-4mole/L x 0.25 L x 55.85 g x 1000mg/( 1g)=37.3g/mole
* Diluted Iron Solution's Absorbance at 0.300 nm
0.300 = 12172 x + 0.0018
X = 2.450 x 10-5mole/L
[ m1v1= m2v2]
X x 25 ml = 2.450 x 10-5mole/Lx 100ml
X = 0.098 x 10-3mole/L (Original concentration)
2.450 x 10-5mole/L x 0.25 L x 55.85 g x 1000mg/( 1g)= 34.2 g/mole
Percent error=(Experimetal value-Actual)/Actual
* Unknown Solution's Absorbance *
Diluted Iron Solution's Absorbance
at 0.500 nmat 0.300 nm
(37.3-35)/35 * 100 = 6.5 % (34.2-35)/35 * 100 = 2.2 %
Table2) Summarizing to find unknown Solution
|
Unknown Identification
|
Absorbance (nm)
|
Concentration of Iron in the Sample solution(M)
|
Concentration of Iron in the Original sample (M)
|
Amount of Iron in Original Sample (mg)
|
% Error
|
|
D
|
0.500
|
4.093 x 10-5
|
1.636 x 10-4
|
37.3
|
6.5
|
|
Diluted Iron Sample
|
0.300
|
2.450 x 10-5
|
0.098 x 10-3
|
34.2
|
2.2
|
Discussion 1)
A. Preparation Diluted Iron Sample
1. I put 20ml of 1.0 M H2SO4 acid in the filtered solution with 35mg of a crushed tablet Iron into the 250 mL of volumetric flask. The reason why the exact amount of 20ml of 1.0 M H2SO4 does not matter is that the amount of ground Iron is already reacted with the acid.
2. And then pipet 25 ml of this filtered solution into a 100ml volumetric flask and dilute iron sample with distilled water.
B. Working Standard Solutions and Sample Solutions
1. I collected Iron stock solution (2.567 x 10-4 M) and unknown solution.
2. Prepared 2mL of diluted iron sample solution and 6 mL of unknown solution in the flasks and pipetted 0, 1, 3, 5, 10 mL of stock solution into each 50 mL of volumetric flask
3. I mixed with 1.0 M ascorbic acid, 4 mL of the sodium acetate solution and 10-phenanthroline solution which is formed an intensely colored orange-red complex into the each prepared seven flasks. I observed different colors in each flasks in accordance with a different amount of stock solution.
C. Determining wavelengthmax(lambdamax) and Measuring the Absorbance
1. By using Spec-20, I could exam different amount of wavelengths with absorbance at 511 nm in each different amount of solutions.
References
1. VIU Chemistry Department. CHEM 140 CHEMISTRY LABORATORY MANUAL, 5th Edition; Nanaimo, BC, 2015.
Discussion 2)
Discuss whether the lab was successful by commenting on your value, the expected value, and the percent error. Discuss how good your calibration curve was based on the R2 Value. Refer to Lab B and discuss whether Beer's Law was followed.
(Beer-Lambert Law -
1. When electromagnetic radiation passes through a layer of sample, it decreases in power.
2. Decreases is proportional to the thinness of sample and the anayte concentration. )
Discussion 3)
Identify and discuss systematic errors that could explain your percent error result. The source of error that you provide must be something inherent to the procedure that you performed or the result of any mistake you made, which deviates significantly from the procedure outlined in the lab manual. You must also explain how this error would have affected your results and explain the sign of your percent error.
Discussion 4)
Reference
2. Robert C. Atkins. Colorimetric Determination of Iron in Vitamin Supplement Tablets. A general chemistry experiment. 1975. 52(8) P550
Conclusion
The unknown sample and diluted Iron sample were determined to be 37.3 mg and34.2 mg, respectively. The concentration and wavelength of the Iron samples and unknown solution were determined by using the spectrophotometry.