[sssssaaaallmaan]

Greetings and thanks for the opportunity to ask these questions. It is really appreciated.

1)
Iron (II) ammonium sulphate-6-water, FeSO4.(NH4)2SO4.6H2O, is a very stable pale green solid and is frequently used as a primary standard in volumetric work. Other Iron (II) salts are, however, much less suitable for this purpose. Can you please suggest why this is so, explaining the likely reasons for this unsuitability common to many Fe (II) compounds.


2)
Could you explain why no indicator is used in titration involving manganate (VII) ions?


3)
Propanone has a boiling temperature of about 56º C and is miscible with water in all proportions. Suggest what might be the purpose of washing the solid FeC2O4.xH2O with propanone and why this effective.

4)
Explain what you can deduce from the fact that the oxidation of Fe2+ ions (by MnO4¯ ) occurs readily at room temperature, but that of C2O4 ²¯  requires a temperature of about 60-70 º C.

5)
If a sample of Iron (II) ethanedioate hydrate was dissolved in dilute sulphuric acid and titrated against manganate (VII) ion until both the cation and the anion were just fully oxidized, could be please indicated what cationic species would then be present in the resulting solution.

6)
Could you please suggest one advantage and one disadvantage of making up a single solution of Iron (II) ethanedioate hydrate in dilute sulphuric acid (by using about 2 g in 250 cm³) and then taking several separate 25 cm³ volumes by pipette, instead of using separately weighed ( about 0.2g) samples.



Thank you for your time and consideration. If anyone can lend a hand to any of the questions i will be totally grateful.

Sal.

[Arkcon]

Greetings and thanks for the opportunity to ask these questions. It is really appreciated.

Greetings and welcome to you as well.  I'm glad you were able to ask your questions.  Presumably, you'd like them answered by us.   But our policy on this board, is to help you, not do it for you.  So we would like to see you start the work.

[sssssaaaallmaan]

Hi, Thank you for the response but sorry about the delay of it. I have been having a couple of busy days lately. Some of the questions i asked, i had the chance to think about and come up with my answers ( IN RED). The rest of the questions, i am still in middle of figuring out. Would it be possible to see how i have done with the following questions?

2)
Could you explain why no indicator is used in titration involving manganate (VII) ions?

Managnate (VII) or permanganate is a very colored solution.
When it is all consumed or is in excess at the end point of an oxidation / reduction titration the purple color is either lost or appears.

The product from the reduction of the managante (VI) ion in acid solution is the colorless Mn2+ ion

H3O + + MnO4− + 5 e− → Mn2+ + 4 H2O

we don't need an indicator because of the deep color of one of the reactants - a self indicator

3)
Propanone has a boiling temperature of about 56º C and is miscible with water in all proportions. Suggest what might be the purpose of washing the solid FeC2O4.xH2O with propanone and why this effective.

Propanone (acetone) boils at a lower degree than water. Since it is miscible, when you mix it with a compound contains residual water and filter it, you exclude all water from it and you will remain with a low-boiling liquid. It helps drying in a faster manner.

4)
Explain what you can deduce from the fact that the oxidation of Fe2+ ions (by MnO4¯ ) occurs readily at room temperature, but that of C2O4 ²¯  requires a temperature of about 60-70 º C.

The high temperature in the latter is required to break the carbon-carbon bonds. However, you don't need any heating to react a monoatomic species

6)
Could you please suggest one advantage and one disadvantage of making up a single solution of Iron (II) ethanedioate hydrate in dilute sulphuric acid (by using about 2 g in 250 cm³) and then taking several separate 25 cm³ volumes by pipette, instead of using separately weighed ( about 0.2g) samples.

The advantage is that it is easier to do that (making 1 solution), and will help you account for errors in the titration itself.. The disadvantage is that it will not reduce or compensate for errors in the weighing of the samples.

Thank you for your time and consideration

Sal.

[sssssaaaallmaan]

I have had a go at trying question 5, if you could check or guide me towards the right way in the question and the other questions i posted , it would be appreciated.

5)
If a sample of Iron (II) ethanedioate hydrate was dissolved in dilute sulphuric acid and titrated against manganate (VII) ion until both the cation and the anion were just fully oxidized, could be please indicated what cationic species would then be present in the resulting solution.

2 Fe2+ + MnO42- + 8H+ = 2 Fe3+ + Mn2+ + 4 H2O

Fe goes from oxidation number +2 to +3 : it is oxidized
Mn goes from oxidation number +6 to +2 : it is reduced

[sjb]

5)
If a sample of Iron (II) ethanedioate hydrate was dissolved in dilute sulphuric acid and titrated against manganate (VII) ion until both the cation and the anion were just fully oxidized, could be please indicated what cationic species would then be present in the resulting solution.

2 Fe2+ + MnO42- + 8H+ = 2 Fe3+ + Mn2+ + 4 H2O

Fe goes from oxidation number +2 to +3 : it is oxidized
Mn goes from oxidation number +6 to +2 : it is reduced

Manganate (VII) is not MnO₄^2- .

[sssssaaaallmaan]

5)
If a sample of Iron (II) ethanedioate hydrate was dissolved in dilute sulphuric acid and titrated against manganate (VII) ion until both the cation and the anion were just fully oxidized, could be please indicated what cationic species would then be present in the resulting solution.

2 Fe2+ + MnO42- + 8H+ = 2 Fe3+ + Mn2+ + 4 H2O

Fe goes from oxidation number +2 to +3 : it is oxidized
Mn goes from oxidation number +6 to +2 : it is reduced

Manganate (VII) is not MnO₄^2- .

Ah, yes. My bad.

2 Fe2+ + MnO4- + 8H+ = 2 Fe3+ + Mn2+ + 4 H2O

Fe goes from oxidation number +2 to +3 : it is oxidized
Mn goes from oxidation number +5 to +2 : it is reduced

[Borek]

2 Fe2+ + MnO4- + 8H+ = 2 Fe3+ + Mn2+ + 4 H2O

Charge is not balanced.

[sssssaaaallmaan]

6Fe 2+ + 8H+ + MnO4- --> Mn2+ + 4 H2O

Thanks.

[Borek]

6Fe 2+ + 8H+ + MnO4- --> Mn2+ + 4 H2O

Charge is not balanced.

Yes, I know. I am boring.

[sssssaaaallmaan]

Equation 1: MnO4- + 8H+ 5e- ===>Mn2+ + 4H2O
Equation 2: Fe2+                  ===> Fe3+ + e-

Multiplying equation 2 by 5 gives:

5Fe2+===> 5Fe3+ + 5e-

Then adding the multiplied equation to equation 1, gives: ( The electrons cancel)

5Fe2+ + MnO4- + 8H+===> 5Fe3+ + Mn2+ 4H2O

If this isn't right, then please show mercy.

[Borek]

5Fe2+ + MnO4- + 8H+===> 5Fe3+ + Mn2+ 4H2O

You see, when you want - you can

[sssssaaaallmaan]

As i posted at the top of this page the following question bugs me a bit.

Iron (II) ammonium sulphate-6-water, FeSO4.(NH4)2SO4.6H2O, is a very stable pale green solid and is frequently used as a primary standard in volumetric work. Other Iron (II) salts are, however, much less suitable for this purpose. Can you please suggest why this is so, explaining the likely reasons for this unsuitability common to many Fe (II) compounds.

You want something that is soluble, stable to light and air, especially one that does not pick up moisture from the air (which changes its assay), crystalline rather than powdery (easier to weigh and transfer as a solid), and inexpensive.

I think I have answered the first part of question( if not please let me know) , but the second part, about reasons for unsuitability of Iron (II) salts I'm having problems with.

If you could show help in any way.

Sal.

[Borek]

the second part, about reasons for unsuitability of Iron (II) salts I'm having problems with.

Do you know what happens to Fe²⁺ exposed to the atmospheric oxygen?

[sssssaaaallmaan]

the second part, about reasons for unsuitability of Iron (II) salts I'm having problems with.

Do you know what happens to Fe²⁺ exposed to the atmospheric oxygen?

Once the Fe2+  has been exposed to the air it will absorbed so much oxygen,
that the Fe2+ ions change to Fe3+ ions and are no longer water soluble.

I hope thats about right.

[sssssaaaallmaan]

Could you please suggest one advantage and one disadvantage of making up a single solution of Iron (II) ethanedioate hydrate in dilute sulphuric acid (by using about 2 g in 250 cm³) and then taking several separate 25 cm³ volumes by pipette, instead of using separately weighed ( about 0.2g) samples.

If you're doing an experiment with it, an advantage would be that all volumes come from the same sample of solution, so they will be consistent. A disadvantage would be that, if there is something wrong with the initial solution, all your results will have errors.
also, for the separately sampled one disadvantage is that pipetting leaves its own errors, meaning total error will increase.


Am i on the right track here?