It is a Chemistry Pre-lab questions. I tried to figure those out, but im getting

Question

It is a Chemistry Pre-lab questions.

I tried to figure those out, but im getting hard time.

1. To what does the term strong oxidizing agent refer? Provide Examples.

2. What is one disadvantage of using the very strong oxidizing agent potassium permanganate as a titrant?

3. What is the purpose of adding the sulfuric acid?(Hint: consider the products of the reaction and their properties)

4. What is the purpose of adding the phosphoric acid at some point of the titration?

5. Provide a step by step procedure for the standardization of a KMnO4 solution.

6. If 45.52 mL of a potassium permanganate solution is needed to titrate 2.145 g of iron(II) ammonium sulfate hexahydrate, calculate the molarity of the KMnO4 solution.

7. A 1.545 g solid sample of an unknown containing iron(II) in the dissolved sample requires 32.85 mL of a 0.025 M KMnO4 solution to reach the pink end point of the titration. Calculate the mass of iron in the sample (in grams) and the percentage of iron in the sample.

For number 6 & 7 , i want the work procedure( i wanna know how it works ) .

Thank you :)

Explanation / Answer

1) That means, if you gain electrons you are reduced - Grrr!
If you lose electrons you are oxidized. Lion!

So an oxidizing agent is a substance that causes other atoms to be oxidized. That is, it causes the other atoms to lose electrons, or to say it the other way, it takes electrons away fromt he other atom, the way that oxygen takes electrons away from other atoms (This may help you to remember how this works if you think about it like this....Iron is oxidized (rusted) the Iron combines with Oxygen to form Fe2 O3 - the iron loses electrons to the Oxygen - the iron is "oxidized" by the oxygen. The oxygen is an oxidizing agent.
But if you had iron and chlorine, it would be chlorine that would be taking the electrons. The iron would still be "oxidized" even if no oxygen were present because it is losing electrons to the chlorine.

2) The advantage is that it acts as a self-indicator i.e. Does not need any indicator while the disadvantage is that it is a strong oxidizing agent therefore reacts vigorously and very fast

3) Depends on the method used. In general, it helps to dissolve all the sample.But in case of using manganometry in the determination, then the acid is needed to ensure low pH, because the reactionFe2+ + MnO4- = Fe3+ + Mn2+proceeds only in high pH. If the pH was neutral or basic, solid MnO2 would be created, which is not favorable (we need to know prpreciselyow many mno4- oxidates one fe2+).

4) Explain how the phosphoric acid helps to sharpen the some point in the titration.
If the solution contains iron as chloride, their presence is detrimental to the analysis results. Iron (III) chloride complexes are yellow, and they can make it difficult to spot the end point. To avoid the problem we can add phosphoric acid to the solution. Phosphate complex has higher stability constant and is colorless.

5) You may have been using a titrant that would reduce MnO2, which would result in a higher-than-actual concentration of KMnO4 being calculated. This would necessitate its removal. Also, if you are using the KMnO4 solution in another reaction, the MnO2 might need to be removed to prevent a reaction with other chemicals or (if a product is being precipitated) to avoid contamination of products.

Filter paper should not be used because KMnO4 will oxidize many organic materials and will be reduced to MnO2 (this causes a brown stain on your skin if you touch the KMnO4). The paper will be stained brown, and more MnO2 will form, which may carry through the filter.

6) the equation for the titration is

5Fe+2 + MnO4- + 8H+ --> 5Fe+3 + Mn+2 + 4H20 ?

Molar mass of FeSO4(NH4)2SO4*6H2O is 392.1406 g/mol

moles of FeSO4(NH4)2SO4 6H2O = 2.145/392.14 = 0.005469

moles of Fe = 0.005469

from the equation , moles of MnO4- = 0.005469 / 5 = 0.0010938

these are in 45.52 mL so moles per liter = 0.0010938 * 1000 / 45.52

= 0.0240 moles per liter KMnO4

7) Supposing *all* of the iron is in the 2+ oxidation state at the beginning of the titration:

5 Fe{2+} + KMnO4 + 8 H{+} ? Mn{2+} + 5 Fe{3+} + K{+} + 4 H2O

(0.03285 L KMnO4) x (0.025 mol/L) x (5 mol Fe / 1 mol KMnO4) x
(55.8452 g Fe/mol) = 0.23 g Fe

(0.23 g / (1.545 g) = 0.15 = 15% Fe

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