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.

WhatsApp_Image_2024-08-28_at_18.07.32_71550851.jpg

iTeachChem Helper•8/28/24, 12:54 PM

@Dexter

iTeachChem Helper•8/28/24, 12:54 PM

Note for OP

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iTeachChem•8/28/24, 1:30 PM

Quick question, can you please elaborate on the formula used here and the numbers you have substituted?

iTeachChem•8/28/24, 1:31 PM

Really cool to see a q on a practically performed experiment.

Techygamey58OP•8/28/24, 1:56 PM

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

Techygamey58OP•8/28/24, 1:57 PM

and finally to find purity % I used strength found/given strength x 100

TTechygamey58 well I just used the simple formula of M1V1=M2V2 in which my teacher told me tha...

iTeachChem•8/28/24, 1:58 PM

so for this first step. you sure this works for this setup?

iTeachChem•8/28/24, 1:59 PM

also there is an a1 a2 there what is that and what numbers have we put there?

IiTeachChem also there is an a1 a2 there what is that and what numbers have we put there?

Techygamey58OP•8/28/24, 2:00 PM

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

Techygamey58OP•8/28/24, 2:02 PM

here's the reaction

WhatsApp_Image_2024-08-28_at_19.32.27_097d9233.jpg

iTeachChem•8/28/24, 2:02 PM

how about this, we do this from first principles?

iTeachChem•8/28/24, 2:03 PM

Interesting. Have you done redox reactions? You aware of N1V1 = N2V2?

IiTeachChem Interesting. Have you done redox reactions? You aware of N1V1 = N2V2?

Techygamey58OP•8/28/24, 2:04 PM

I was unable to cover that chapter thoroughly, please explain me.

TTechygamey58 I was unable to cover that chapter thoroughly, please explain me.

iTeachChem•8/28/24, 2:07 PM

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

iTeachChem•8/28/24, 2:08 PM

Now, even if we balance,

iTeachChem•8/28/24, 2:08 PM

the ratio is 5:1 ~~and not 10:4(which is 5:2)~~ edit: this is correctly done by you

iTeachChem•8/28/24, 2:08 PM

do you see that?

iTeachChem•8/28/24, 2:09 PM

https://ncert.nic.in/pdf/publication/sciencelaboratorymanuals/classXI/chemistry/kelm206.pdf

iTeachChem•8/28/24, 2:09 PM

the formula you have used is from here where a1 and a2 are acidity and basicity of acids and bases.

iTeachChem•8/28/24, 2:09 PM

here, we are doing a redox titration

iTeachChem•8/28/24, 2:12 PM

this is the formula :D

iTeachChem•8/28/24, 2:12 PM

normality = molarity x volume

iTeachChem•8/28/24, 2:14 PM

but yea M2 does come out to be 1/80 (two incorrect thingies made it correct lol)

iTeachChem•8/28/24, 2:17 PM

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

iTeachChem•8/28/24, 2:17 PM

perhaps an error in measuring the 4 ml? if you change that to 4.5 makes it 97.5 %

Techygamey58OP•8/28/24, 2:19 PM

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"

Techygamey58OP•8/28/24, 2:20 PM

now here by experiment it took me and my friends 4ml of KMnO4 to turn 10ml of mohr's salt solution pink via titration

TTechygamey58 now here by experiment it took me and my friends 4ml of KMnO4 to turn 10ml of mo...

iTeachChem•8/28/24, 2:23 PM

haan wahi if you go 4 to 4.5 the purity is 97.5

iTeachChem•8/28/24, 2:23 PM

your calc is correct although formula thoda upar neeche tha, but the substitution was correct

Techygamey58OP•8/28/24, 2:23 PM

aw man that was heavy

Techygamey58OP•8/28/24, 2:24 PM

thank you sir for your help and patience

TTechygamey58 thank you sir for your help and patience

iTeachChem•8/28/24, 2:24 PM

most welcome

TTechygamey58 aw man that was heavy

iTeachChem•8/28/24, 2:24 PM

which part?

iTeachChem•8/28/24, 2:24 PM

the general idea is that electrons take part in a reaction. this n1v1 or m1v1a1 is just accounting for those electrons in a way

iTeachChem•8/28/24, 2:24 PM

mass of stuff that reacts with 1 mole of electrons = number of equivalents, that is what is used for normality

iTeachChem•8/28/24, 2:25 PM

m1v1 a1 (actually m1v1x n factor) is the same as n1 v1 :)

iTeachChem•8/28/24, 2:25 PM

anyway check the videos out for that if you like

Techygamey58OP•8/28/24, 2:25 PM

that is exactly where I was stuck

Techygamey58OP•8/28/24, 2:25 PM

thank you so much

Techygamey58OP•8/28/24, 2:26 PM

+solved iTeachChem

iTeachChem Helper•8/28/24, 2:26 PM

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