titration
so yeah, I did titration with KMnO4 and mohr's salt solution today in which I need to find the molarity and percentage purity of the KMnO4 solution when the molarity of mohr's salt solution is M/40 and here is the observation and calculation I did (attached). I got percentage purity about 105% I mean what!? tell me if it's true or where I fucked up.
18 Replies
@Dexter
Note for OP
+solved @user1 @user2... to close the thread when your doubt is solved. Mention the users who helped you solve the doubt. This will be added to their stats.Quick question, can you please elaborate on the formula used here and the numbers you have substituted?
Really cool to see a q on a practically performed experiment.
well I just used the simple formula of M1V1=M2V2 in which my teacher told me that those 'a' values need to be memorized for finding the molarity
then for finding the strength I used Molarity x molar mass
and finally to find purity % I used strength found/given strength x 100
so for this first step. you sure this works for this setup?
also there is an a1 a2 there what is that and what numbers have we put there?
That's exactly what my teacher told us to memorize. I just only know that it came from balancing the redox reaction that occurs here
here's the reaction
how about this, we do this from first principles?
Interesting. Have you done redox reactions? You aware of N1V1 = N2V2?
I was unable to cover that chapter thoroughly, please explain me.
Hard to explain over texts, you can check out videos here, or read up on the concept of normality. That helps us do this without balancing the reaction.
https://youtu.be/YrC0N5R-0H8
Now, even if we balance,
the ratio is 5:1 and not 10:4(which is 5:2) edit: this is correctly done by you
do you see that?
https://ncert.nic.in/pdf/publication/sciencelaboratorymanuals/classXI/chemistry/kelm206.pdf
the formula you have used is from here where a1 and a2 are acidity and basicity of acids and bases.
here, we are doing a redox titration
this is the formula :D
normality = molarity x volume
but yea M2 does come out to be 1/80 (two incorrect thingies made it correct lol)
not sure where you went wrong dude, you have taken the mass to be 1.8 gms in your calc although that is not mentioned in your original statement, assuming that to be correct
perhaps an error in measuring the 4 ml? if you change that to 4.5 makes it 97.5 %
here is the full question: "you are supplied with M/40 standard solution of ferrous ammonium sulphate (mohrs salt) solution. Find out percentage purity of impure KMnO4 sample, if 1.8gm of which have been dissolved per litre of the solution"
now here by experiment it took me and my friends 4ml of KMnO4 to turn 10ml of mohr's salt solution pink via titration
haan wahi if you go 4 to 4.5 the purity is 97.5
your calc is correct although formula thoda upar neeche tha, but the substitution was correct
aw man that was heavy
thank you sir for your help and patience
most welcome
which part?
the general idea is that electrons take part in a reaction. this n1v1 or m1v1a1 is just accounting for those electrons in a way
mass of stuff that reacts with 1 mole of electrons = number of equivalents, that is what is used for normality
m1v1 a1 (actually m1v1x n factor) is the same as n1 v1 :)
anyway check the videos out for that if you like
that is exactly where I was stuck
thank you so much
+solved iTeachChem
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