molarity-->normality

[datdat]

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simple titration problem in kbb p.946,
(titrate .05L of 4M HCL with 3M NaOH)

it convert 4M HCl ---> 4N HCL
3M NaOH---> 3N NaOH

How could this be possible?

when should I treat molarity as normality?

 

[UCB05]

simple titration problem in kbb p.946,
(titrate .05L of 4M HCL with 3M NaOH)

it convert 4M HCl ---> 4N HCL
3M NaOH---> 3N NaOH

How could this be possible?

when should I treat molarity as normality?

Normality is a superficial concept. You can get through all of chemistry without ever know what it means, as long as you use some logic. For titration, 1M HCl contributes 1M H+, or 1N. 1M H2CO3 would contribute 2M H+, or 2N per 1M acid. Normality makes that distinction.

If I were to look at that problem, I would not have even bothered to consider normality since 1M => 1N for both the base and acid. And even if you were given a diprotic acid instead, if you have the good sense to realize you get twice the bang for the buck and take that into account, you wouldn't need normality to tell you that.

 

[marscole]

You can treat normality as for example.... NaOH has ONE equivalent of OH- and will react with ONE equivalent of H+ to form H2O.

For example,
H2SO4 has 2 equivalent of protons.

Mg(OH)2 has 2 equivalent of hydroxides.

Sample exercise:
15 mL of 0.5 M H2SO4 will react with 20 mL of Al(OH)3. What're the molarity and normality of Al(OH)3?

Try this of you understand it.... Good luck!!!😎

 

[NumbaOneStunna]

This is the trouble I have with normality, see if you can help me. I don't get why H2SO4 has 2 equivalents of Hydrogen to give off. I know it has to hydrogens that can be deprotenated, but isn't the second one much harder to give off?

Will H2SO4 have 2 equiv of H in water when it dissociates?
Or does H2SO4 only have 2 equiv of H when reacting with a base (how strong or how weak?) that is strong enough to almost always deprot the second proton (provided there is enough base)

 

[marscole]

Assuming they all go into completion. (I know HSO4- is much weaker to dissociate!!!)

 

[NumbaOneStunna]

Assuming they all go into completion. (I know HSO4- is much weaker to dissociate!!!)

How do we know when it goes to completion? I understand stuff like Ba(OH-)2 will dissociate fully in water b/c it's ionic. But that's not the case for H2SO4, can someone give me a detailed explanation of what Im supposed to do when I see something with more than 1 ionizable proton?

 

[marscole]

Use M1V1 = M2V2 to find molarity....
When normality, you can used the above equation as well....
(2)(15 mL)(0.5) = (3)(20 mL) (N)
2 = how many equivalent proton does H2SO4 have...
3 = how many equivalent hydroxide does Al(OH)3 have...

N = (2*15*0.5) / (3*20) = 0.25 N of Al(OH)3

M = (15*0.5)/(2*20) = 0.1875 M of Al(OH)3

😉