1. (5 pts) Stock solution B is made in dimethylsulfoxide (DMSO) instead of water
ID: 568114 • Letter: 1
Question
1. (5 pts) Stock solution B is made in dimethylsulfoxide (DMSO) instead of water. Why do you suppose this is the case? 2. (5 pts) Do acidic or basic conditions facilitate our experiment, and why? Explain the role of acetate buffer in this regard. 3. (5 pts) Consult Step 2 in the Procedure. In table format, detail the necessary dilutions to make the calibration standards. Make two copies of this table, hand one in and keep the other to help you during the experiment. (Note that you cannot measure less than 1 mL accurately with your apparatus, so how will you handle this for the 0.1 mg/L standard?) A sample calculation appears below for making the 1 mg/L dilution standard. mg/L of Fe 0.1 mL of A mL of B mL of C 0.25 Prof AKU CHEM 24OL SPI8 Lab #5 How Much Iron is Really in That Pill? 0.5 4. (2 pts) Again referring to Step 2 in the Procedure, how would you prepare the "blank" sample?Explanation / Answer
1. Orthophenanthroline is an organic compound and has aromatic ring in it. This makes orthophenanthroline insoluble in water and soluble in organic solvents like alcohol, acetone, benzene etc. That is why it is dissolved in DMSO in this experiment to make the stock solution.
2. Yes, the acidic or basic conditions facilitate the reaction. In here, orthophenanthroline forms a colored complex with Fe2+. But Fe2+ can also oxidise to Fe3+ which is also capable of forming the complex with orthophenanthroline. Acetate buffer is added to the reaction to keep the pH 4. This will avoid the formation of Fe3+ from Fe2+ and thus Fe3+ would not be able to form complex.
3. Ferrous ammonium sulfate hexahydrate stock solution = 10 mg/L
Total volume required = 50 ml
For solution 1, desired Fe concentration = 0.1 mg/L
So, we use formula, C1V1 = C2V2
10*V1 = 0.1*50
V1 = 0.5 ml
orthophenanthroline available in stock solution = 5 g/L
total volume = 50 ml
desired concentration = 0.5 g/L
C1V1 = C2V2
5*V1 = 0.5*50
V1 = 5 ml
Similarly, we can calculate for hydroquinone:
hydroquinone available in stock solution = 1%
total volume = 50 ml
desired concentration = 0.02%
C1V1 = C2V2
1*V1 = 0.02*50
V1 = 1 ml
The volumes of hydroquinone and orthophenanthroline will remain same in all the solutions.
For the Fe, we can just do the same calculations and calculate. The table will be:
4. To prepare the blank sample, we will not add any Fe stock solution to the volumetric. We will take 5 ml of orthophenanthroline, 1 ml of hydroquinone and rest buffer solution to make 50 ml total.
mg/L of Fe ml of A ml of B ml of C 0.1 0.5 5 1 0.25 1.25 5 1 0.5 2.5 5 1 1 5 5 1 2 10 5 1 4 20 5 1Related Questions
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