10+ Oxidimetry (Analytical Chemistry) Questions and Discussion – Oxidimetry is one type of chemical reaction used in volumetric analysis is an oxidation-reduction reaction. This type of reaction involves the transfer of electrons between the oxidizing agent and reducing agent.
The term oxidation refers to any chemical change in which the oxidation state increases, while reduction refers to any decrease in oxidation state. An oxidizing agent is a compound in which the atoms contained have decreased oxidation states. On the other hand, in the reducing agent, the atoms contained have an increase in oxidation number. Many redox titrations are carried out using color indicators.
In many analytical procedures, the analyte exists in more than one oxidation state and must be converted to a single oxidation state prior to titration. The redox reagents used must be capable of converting the analyte completely and rapidly into the desired oxidation state.
1 – 10 Oxidimetry Problems and Discussion
1. In a determination of the level of ferrous sulfate (MR = 278) using the permanganometry method, it was found that the volume of 0.1 N potassium permanganate required to achieve TAT was 10 ml. How many grams of ferrous sulfate are used up in the reaction if the following equations are known:
1 ml of 0.1 N potassium permanganate is equivalent to 27.80 mg of ferrous sulfate
1 ml KMnO4 0.1 N 27.80 mg FeSO4
10 ml KMnO4 0.1 N X mg FeSO4
x = 10 x 27.80 mg
= 278 mg
2. How many milligrams of FeSO4 (MR = 278) must be weighed if the mole of FeSO4 is 0.1 mol?
3. Calculate the normality of citric acid (20 ml) determined using the acid-alkalimetric titration method if it is known that the volume of 0.1 N HCL used for the titration is 5 ml!
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4. In determining the levels of vitamin C using iodimetry, it is known that the number of samples that react is 0.02 Molar. If the mass of vitamin C used is 141 mg and the MR of vitamin C is 176.17, calculate the volume of vitamin C used!
5. An infusion solution contains NaCl as much as 0.85% w/v. If 10 ml of the solution is used to determine the NaCl concentration, how many milligrams of NaCl is theoretically contained in the sample solution?
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6. 20 tablets of sulfamethoxazole were weighed carefully and then powdered. The total weight of the scales is 12 grams. A total of 0.3 grams of the powder was used for assay using nitrimetric titration with the following procedure:
0.3 grams of powder plus 5 ml of dilute HCl and 50 ml of water. Cooled to 15°C then titrated with 0.05M sodium nitrite until 1 drop of the solution immediately gives a blue color to starch iodide paper. It takes 15 ml of 0.05 M sodium nitrite.
If it is known that the sulfamethoxazole content per tablet is 400 mg, determine the sulfamethoxazole concentration! (valence 2, MR of sulfamethoxazole = 253.28)
7. In a spectrophotometric practicum, you want to make a standard solution of salicylic acid with a concentration of 500 ppm. If the desired volume is 1000 ml, determine how many grams of salicylic acid should be weighed?
8. From the problem above, if you want to make a dilution of the parent standard to 20 ppm in a 100 ml flask, determine how many ml of the parent standard must be pipetted!
9. Iodometry problem determine:
a. 10 ml of sodium thiosulfate injection was added with dilute HCL to a pH of approximately 7, then diluted with sufficient water to approximately 20 ml. After being titrated using a starch indicator, it turns out that it requires 40.20 ml of 0.1N iodine solution.
b. What % w/v of Na2S4O3.5H2O in sodium thiosulfate injection is 1 ml 0.1 N is equivalent to 24.82 mg Na2S4O3.5H2O
a. 2Na2S2O3 + I2 → 2NaI + Na2S4O6
Mg sodium thiosulfate = 40.20 x 24.82mg
= 997.8 mg
= 0.9978 g
b. %b/v Na2S4O3.5H2O = 0.9978/10 x 100
10. In making Na2SO3: 15 ml 0.1 M iodine solution is added to Erlenmeyer, add a few drops of starch indicator, titrate with Na2SO3 solution until it is colorless (get V Na2S2O3 = 22 ml). Then 20 ml of CuSo4 + 5 ml of 2 M H2SO4 + 0.5 grams of KI, the mixture is yellow + starch solution / starch indicator slowly until the color is purplish. Titrate with Na2S2O3 until the purple color disappears (get V Na2S2O3 = 8.5 ml). What is the CuSo4 content?
V I2 = 15 ml
M I2 = 0.1 M
V Na2S2O3 = 22 ml
V CuSO4 = 20 ml
V H2SO4 = 5 ml
M KI = 0.5 gr
M H2SO4 = 2 M
V starch solution = 4 ml (80 drops)
V Na2S2O3 = 8.5 ml
- So the standardization of Na2S2O3 against I2
V1.N1 = V2.N2
15 x 0.1 = 22 x N2
N2 = 1.5/ 22 = 0.07 N
11. In an acidic atmosphere, iron (II) is titrated with 0.0206 M potassium permanganate solution, 40.20 mL of KMnO4 solution is required. Calculate the mg of iron in the solution?
In sour conditions:
MnO4- + 8H++ 5e → Mn2+ + 4H2O x 1
Fe2+ → Fe3++ ex 5
MnO4-+ 8H+ + 5Fe2+ → Mn2+ + 4H2O + 5Fe3+
At the equivalence point:
Mol KMnO4 = MV
Mol KMnO4 = MV
= 0.0206 M x 40.2 mL
= 0.828 mmol
5 moles of Fe 1 mole of KMnO4
moles of Fe required = 5 x 0.828 mmol
= 4.14 mmol
The amount of Fe needed is:
= 4.14 mmol Ar.Fe.
= 231.8 mggram
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