gchem M1V1 OR N1V1 ....

[HoangDDS]

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when do we use M1V1=M2V2 vs N1V1=N2V2?

 

[Thundercatz]

when do we use M1V1=M2V2 vs N1V1=N2V2?

Hoang,

You would use N1V1 if the acid donates more than one proton or if the base has more than one OH.

 

[osimsDDS]

Hoang,

You would use N1V1 if the acid donates more than one proton or if the base has more than one OH.

yea this is true, either polyprotic acid or base...

ex/ H2SO4 has 2 equivalent H+ ions therefore you would multiply the Molarity that they give you or that you have to find by 2 which will give you Normality...

Its also good to note that normality is ALWAYS going to be higher than molarity (assuming polyprotic acid/base of course)...

 

[HoangDDS]

Got it! Thanks guys.

Use normality when its polyprotic donation of OH- or H+.

Also I find it useful that :
in monoprotic acid or base (HCl, HBr, NaOH, or KOH) N=M
in diprotic acid or base ( Ca(OH)2 or H2SO4) N=2M

thanks again.

 

[klutzy1987]

You use m1v1 for dilution only. Everything else you use n1v1

 

[HoangDDS]

30ml of .2M Ba(OH)2 is required to neutralize 25ml of citric acid (H3C6H507). what is the molarity of citric acid?

So before I asked this thread, I did it M1V1 = M2V2
where M1 =.2 V1=30ml, and V2= 55ml solve for M2
and I got M < .015 (approximated)

Then I did it over, b/c I guess I was suppose to you Normality,
so N1v1....
N1=.4N (b/c .2M Ba(OH)2 dissocaites into 2 --- .2M x 2 = .4N)
V1=30ml, V2 =25m
which gives me 12/25 which is approx =.5, but they asked for molarity so I had to multiplied this by 3, since citric acid had 3 ionizeable protons.
therefore, the final answer was .5 x 3 = .15

Both ways gave me the right answer! Correct answer was 0.167. I would've picked that anyways since all other choices was really off.

I'm just saying was this just luck, that I did it using M1V1 and got it right with less work?

 

[klutzy1987]

30ml of .2M Ba(OH)2 is required to neutralize 25ml of citric acid (H3C6H507). what is the molarity of citric acid?

So before I asked this thread, I did it M1V1 = M2V2
where M1 =.2 V1=30ml, and V2= 55ml solve for M2
and I got M < .015 (approximated)

Then I did it over, b/c I guess I was suppose to you Normality,
so N1v1....
N1=.4N (b/c .2M Ba(OH)2 dissocaites into 2 --- .2M x 2 = .4N)
V1=30ml, V2 =25m
which gives me 12/25 which is approx =.5, but they asked for molarity so I had to multiplied this by 3, since citric acid had 3 ionizeable protons.

I'm just saying was this just luck, that I did it using M1V1 and got it right with less work?

Neutralized is always n1v1 if you go the right answer it is because either you made a mistake or you got very lucky. Also .5 times 3 is 1.5 which is very different than what you got.

 

[polarmolar]

So just to make sure I got this...

If you see more than one OH or H in a molecule THEN you use N1V1?

 

[HoangDDS]

Neutralized is always n1v1 if you go the right answer it is because either you made a mistale or you got very lucky.

I guess I made a mistake then got lucky. B/c I used V2 as the total volume, which was 55ml when I was using M1V1.

and the book has it to use V2 = 25ml using N1V1.

So V2 is not the total volume? It's the volume of the citric acid that I am trying to neutralize?

 

[HoangDDS]

Actually, now that i'm really thinking about it. The correct way is use to V2 as the vol of citric acid that I am trying to neutralize, not the overall volume --- since I am setting them equal to each other. DOH!

 

[klutzy1987]

Actually, now that i'm really thinking about it. The correct way is use to V2 as the vol of citric acid that I am trying to neutralize, not the overall volume --- since I am setting them equal to each other. DOH!

LOL everyone makes mistakes, dont worry youll be fine.