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### Topic: Oxidation of iron(2) sulfate- heptahydrate  (Read 9364 times)

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#### Science geek

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##### Oxidation of iron(2) sulfate- heptahydrate
« on: July 23, 2015, 07:33:00 AM »
How many grams of iron(2) sulfate heptahydrate (pH<7) can be oxidized with 28 cm3 potassium permanganate solution ,concentration of 0,02 mol/dm3.

I am aware of that this problem is actually so easy but there is no way that my result matches with the result in the book
I wrote the equation,like this:
2 KMnO4 + 10 FeSO4 + 8 H2SO4 --> 5 Fe2(SO4)3 + 2 MnSO4 + 1 K2SO4 + 8 H2O
H2SO4 is needed because acidic environment is needed for the reaction to take place. There is no way that iron (2) sulfate-heptahydrate can directly oxidize with KMnO4.I am sure that this equation is correct. Than I founded the ammount of KMnO4.
c=n/V
n=c*V=0,02*0,028=0,00056 mol
But I can not determine the mole ratio,according to the chemical reaction, I am so confused
n(FeSO4*7H2O); n(KMnO4)=x:x
The result should be: 0,7747g of FeSO4*7H2O

#### Dan

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #1 on: July 23, 2015, 08:01:17 AM »
I wrote the equation,like this:
2 KMnO4 + 10 FeSO4 + 8 H2SO4 --> 5 Fe2(SO4)3 + 2 MnSO4 + 1 K2SO4 + 8 H2O

But I can not determine the mole ratio,according to the chemical reaction, I am so confused
n(FeSO4*7H2O); n(KMnO4)=x:x

I don't understand the confusion - you have written the ratio in the balanced chemical equation already...
My research: Google Scholar and Researchgate

#### Science geek

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #2 on: July 23, 2015, 08:09:23 AM »
You mean the ratio 10:2
But then the result is incorrect

#### Hunter2

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #3 on: July 23, 2015, 08:10:19 AM »
How many grams of iron(2) sulfate heptahydrate (pH<7) can be oxidized with 28 cm3 potassium permanganate solution ,concentration of 0,02 mol/dm3.

I am aware of that this problem is actually so easy but there is no way that my result matches with the result in the book
I wrote the equation,like this:
2 KMnO4 + 10 FeSO4 + 8 H2SO4 --> 5 Fe2(SO4)3 + 2 MnSO4 + 1 K2SO4 + 8 H2O
H2SO4 is needed because acidic environment is needed for the reaction to take place. There is no way that iron (2) sulfate-heptahydrate can directly oxidize with KMnO4.I am sure that this equation is correct. Than I founded the ammount of KMnO4.
c=n/V
n=c*V=0,02*0,028=0,00056 mol
But I can not determine the mole ratio,according to the chemical reaction, I am so confused
n(FeSO4*7H2O); n(KMnO4)=x:x
The result should be: 0,7747g of FeSO4*7H2O

You can see the ratio between Permanganate and iron sulfate in the equation.
You calculate already the moles of the Permanganate. The rest is simple mathematics. You need two multiplication . The moles times the ratio and times the molar mass oft iron salt. Don't forget the water.

#### Hunter2

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #4 on: July 23, 2015, 08:11:23 AM »
You mean the ratio 10:2
But then the result is incorrect

Why is it incorrect. Show your mathematics.

#### Science geek

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #5 on: July 23, 2015, 08:21:50 AM »
c=n/V
n=c*V=0,02*0,028=0,00056 mol
n(FeSO4*7H2O); n(KMnO4)=10:2
n(FeSO4*7H2O): 0,00056mol=10:2
n(FeSO4*7H2O)=0,0028 mol
n=m/M
m=n*M=0,0028*333,84 mol=0,935 g (incorrect)
The result should be: 0,7747 g

#### Science geek

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #6 on: July 23, 2015, 08:30:17 AM »
Sorry,omg this gooogle. Trust me never use google while sloving problems the molar mass of FeSO4*7H2O is not 333,84 it is like 277,86g/mol. Sorry and thanks. I can not belive I lost 2 hours doing literarly nothing just staring at this problem.

#### Science geek

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #7 on: July 23, 2015, 08:30:56 AM »

#### Hunter2

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #8 on: July 23, 2015, 08:55:38 AM »
Sorry,omg this gooogle. Trust me never use google while sloving problems the molar mass of FeSO4*7H2O is not 333,84 it is like 277,86g/mol. Sorry and thanks. I can not belive I lost 2 hours doing literarly nothing just staring at this problem.

Where did you found the wrong molar mass?

http://www.sigmaaldrich.com/catalog/product/sial/f7002?lang=fr&region=FR

#### Science geek

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #9 on: July 23, 2015, 09:00:28 AM »

#### Hunter2

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #10 on: July 23, 2015, 09:32:50 AM »
But this molecule if it would existing would never have a higher molar mass. Flourine is 19 g/mol time 2 = 38 g//mol to Iron with 55 g/mol

But never mind.

#### Arkcon

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##### Re: Oxidation of iron(2) sulfate- heptahydrate
« Reply #11 on: July 23, 2015, 10:08:32 AM »
Sorry,omg this gooogle. Trust me never use google while sloving problems the molar mass of FeSO4*7H2O is not 333,84 it is like 277,86g/mol. Sorry and thanks. I can not belive I lost 2 hours doing literarly nothing just staring at this problem.

You won't have Google on an exam, but you will likely have a periodic table.  So get in the habit of summing atomic masses quickly.  Also, skip general google search and go straight to wikipedia for molecular mass.  I used to say those numbers were audited by ACS for illicit changes, and I can't actually prove that.  But still, those chemical and physical constants have never steered me wrong.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.