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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: zibb3r on March 10, 2011, 06:57:30 pm

Title: Determination of iron in lawn fertiliser
Post by: zibb3r on March 10, 2011, 06:57:30 pm: If any of you guys did/understand this SAC can you please tell me:

If you analysed a commercial fertiliser and your result for the percentage of iron was less than the manufacturers specification, account for any differences?

~My partner was making the standard solution and went over the mark when adding the deionised water so he poured some out.

Is this a reason for a difference? if so how could I explain it on a SAC?

Thanks :) :)
Title: Re: Determination of iron in lawn fertiliser
Post by: huaxiadragon on March 10, 2011, 07:09:24 pm: Assuming you react the standard solution against the solution containing the iron ions.
Usually if you went a bit over the mark it shouldn't matter too much.
But from your error that should have made the percentage of iron higher than usual. So spilling is not really the cause of error.

Hmm...the only thing I can think of now is perhaps the iron solution didn't completely react with the standard solution?
Or maybe the manufacturer is just cheap and deliberately added less than intended
Title: Re: Determination of iron in lawn fertiliser
Post by: zibb3r on March 10, 2011, 07:38:24 pm: Why is it necessary to add H₂SO₄ to the fertiliser solution before it is titrated with the KMNO₄ solution???
Title: Re: Determination of iron in lawn fertiliser
Post by: huaxiadragon on March 10, 2011, 07:43:17 pm: $MnO^{4-}_{(aq)} + 8H^{+}_{(aq)} + 5e^{-} => Mn^{2+}_{(aq)} + 4H_{2}O_{(l)}$

The reduction of permanganate required hydrogen ions
Where are we going to get it from
Sulfuric acid of course!
Title: Re: Determination of iron in lawn fertiliser
Post by: Jiishwa on March 10, 2011, 07:45:49 pm: The acid is added so the reaction can take place - H+ reacts with oxygen in KMnO4 to form water.