Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Topic started by: leena on August 20, 2009, 10:40:52 AM

Title: Titration and conversion.
Post by: leena on August 20, 2009, 10:40:52 AM

Q1) A solution contains Fe²⁺ and Fe³⁺. 25cm³ of the above solution was taken in a titration flask,acidified with dil. sulphuric & titrated with 0.1M KMnO4 solution.The volume of KMnO4 needed = 12.5ml.
Another 25ml of the original solution was taken & excess SO2 was passed through it,then the solution was boiled & cooled acidified & the resulting sol' required 37.5ml of 0.1M KMnO4 for complete neutralisation.Calculate the concentration of Fe²⁺ and Fe³⁺ in the original solution.


Just wanted to makesure I've understood the problem.
Initially,on reacting with acidified permanganate,Fe²⁺ gets oxidised to Fe³⁺ so we can find the no. of moles of Fe²⁺ from this.
Then when SO2 was passed ,Fe3+ gets reduced to Fe2+ and so we can find the no. of moles of Fe3+  ?


Q2) State how you could obtain pure Mg from Carnalite.

Heat the mineral(KCl.MgCl₂.6H₂O) until all the water evaporates,then add excess NaOH and filter.Residue contains Mg(OH)₂.
Then add HCl to the residue?and electrolyse MgCl₂ ?


I would really appreciate a quick response cause my chem test's in a few hours.

Thank you.

Title: Re: Titration and conversion.
Post by: Borek on August 20, 2009, 10:50:35 AM

First one - close, but to be precise - SO₂ is for reducing Fe³⁺ so that you can determine total iron.

Second one - what is the sense of roasting the solid to dehydrate it, if in the next step you will be putting it to water solution?

Title: Re: Titration and conversion.
Post by: leena on August 20, 2009, 10:58:12 AM

Quote from: Borek on August 20, 2009, 10:50:35 AM

First one - close, but to be precise - SO₂ is for reducing Fe³⁺ so that you can determine total iron.

Yes.I see now.Thanx.

Quote

Second one - what is the sense of roasting the solid to dehydrate it, if in the next step you will be putting it to water solution?

Ok so would simply adding NaOH,filtering and electrolysing the residue work ?

Title: Re: Titration and conversion.
Post by: leena on August 20, 2009, 11:36:14 AM

Q3) Indicate how the following conversions could be effected

a) N₂ -------------> KNO₃

b) NaCl -------------> PbCrO4

c) CuFeS2 -----------> S


No idea how to do part a) and b).I hope someone could atleast tell me how to start the conversion.

For c),
burn CuFeS2,SO2 evolves and add H2S ,S can be obtained ?


thx.

Title: Re: Titration and conversion.
Post by: sjb on August 20, 2009, 01:05:41 PM

Quote from: leena on August 20, 2009, 11:36:14 AM

Q3) Indicate how the following conversions could be effected

a) N₂ -------------> KNO₃

b) NaCl -------------> PbCrO4

c) CuFeS2 -----------> S

For dinitrogen to KNO₃, perhaps look at the nitrogen cycle.

As to b), seems very much like alchemy, are you sure that's what you've been asked to try and do?

Title: Re: Titration and conversion.
Post by: Borek on August 20, 2009, 03:44:06 PM

Could be the question is how to produce equimolar (or equimolar multiply) amount of the other substance.

Title: Re: Titration and conversion.
Post by: leena on August 22, 2009, 07:41:32 AM

Quote from: sjb on August 20, 2009, 01:05:41 PM

As to b), seems very much like alchemy, are you sure that's what you've been asked to try and do?

Not too sure what alchemy means,but if you're saying the question can't be done,I guess that's possible,cause there have been mstakes in my worksheet before.

Quote from: Borek on August 20, 2009, 03:44:06 PM

Could be the question is how to produce equimolar (or equimolar multiply) amount of the other substance.

I don't know but I've posted the question exactly how it appears in my worksheet.

thx.