Stoichiometry doubts...

BITSAT 2015 Guidance › Physical Chemistry questions › Stoichiometry doubts...

Q) 2.6g sample of pyrolusite was boiled with 65ml of N oxalic acid and excess of dil. H₂SO₄. The liquid was then filtered and the residue washed. The filtrate and the washing were mixed and made upto 500ml. 100ml of this soln required 50ml of N/10 KMnO₄. Calculate %purity of pyrolusite.

#Chemistry #Physical Chemistry

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6 Answers

11

vaibhav sharma ·2010-07-14 11:01:04

nyc question but im not able to make out the reactions occuring in this question...how does mno2 react with oxalic acid

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23

qwerty ·2010-07-14 11:15:58

Most probably Mn shud change frm 4+ to 2+

and C frm 2+ to 4 +

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11

vaibhav sharma ·2010-07-15 06:43:42

+2 to +4 ??
shouldn't it be +3 (in oxalic acid) to +4(maybe in co2)

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23

qwerty ·2010-07-15 08:32:01

very sorry yaar , ha +3 hoga typed in a hurry

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zzzzzzzzzzzz ·2010-07-16 23:55:44

is it 66.9%?

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1

Avinav Prakash ·2010-07-17 04:07:38

mili eq of acid added=65
mili eq of acid left after oxidation in 500 ml=25
mili eq of acid used=mili eq of MnO₂=40

n factor of MnO₂=2

w=40*(87/2)*(1/1000)=1.74g

% purity=w/2.6*100= 67%(approx.)

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