destroyer chemistry #70

[socloseithurts]

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I really don't understand the concept of Normality. For example, the question asks:
Consider the reaction of 2.5 dichromate: Cr2O7-2 --> Cr+3 (acidic medium)
What would be the solution Normality if the reaction goes to completion? Ans: 7.5


Can someone explain this please? Thanks in advance 🙂

 

[doc toothache]

I really don't understand the concept of Normality. For example, the question asks:
Consider the reaction of 2.5 dichromate: Cr2O7-2 --> Cr+3 (acidic medium)
What would be the solution Normality if the reaction goes to completion? Ans: 7.5
Can someone explain this please? Thanks in advance 🙂

In oxidation reduction the normality is equal to the molarity divided by the change in the oxidation state.

 

[klutzy1987]

In oxidation reduction the normality is equal to the molarity divided by the change in the oxidation state.

Isnt it the normality is equal to the molarity multiplied by the change in the oxidation state?? This never was my strong point but i think i am correct.

 

[doc toothache]

Isnt it the normality is equal to the molarity multiplied by the change in the oxidation state?? This never was my strong point but i think i am correct.

N = M/change in oxidation state or
M = N x change in oxidation

 

[klutzy1987]

So then work this problem out and you get
N=2.5/3
N=5/6
The correct answer here is 7.5.

M=2.5
Change in Ox=3
M*Change=N
3*2.5=7.5

Correct me where i am wrong.

 

[doc toothache]

So then work this problem out and you get
N=2.5/3
N=5/6
The correct answer here is 7.5.
M=2.5
Change in Ox=3
M*Change=N
3*2.5=7.5
Correct me where i am wrong.

N = M x change in oxidation state.

 

[unitix]

I'm pretty sure N = M * deltaO, N = 2.5 * (6-3) = 7.5 🙂

 

[socloseithurts]

so, do we ever need to know normality in a non-oxidation/reduction problem?

 

[klutzy1987]

so, do we ever need to know normality in a non-oxidation/reduction problem?

Are you kidding, all titration/neutralization problems are involving Normality. Know how to use Normality cold it will definitely pop up on your DAT.
In titration/neutralization, N=M*i, where I is equal to the number of dissociated protons or hydroxides. A 2M of H2SO4 is 4 Normal.

 

[socloseithurts]

Are you kidding, all titration/neutralization problems are involving Normality. Know how to use Normality cold it will definitely pop up on your DAT.
In titration/neutralization, N=M*i, where I is equal to the number of dissociated protons or hydroxides. A 2M of H2SO4 is 4 Normal.

so, when do we use the M1V1=M2V2 formula? seems like every time i try to use it, I should be using normality instead.

 

[klutzy1987]

so, when do we use the M1V1=M2V2 formula? seems like every time i try to use it, I should be using normality instead.

You use M1V1 when you are diluting otherwise use N1V1.

 

[JBarr29]

yeah pretty much the only time you will use M1V1 is when diluting with the same titrate. Like 10M HCl in 20 ml and you want 5 M HCl. How many mLs. Problems like that, as Klutzy said dilutions.