Titration question: from chads videos

[rmm30]

considering the following rxn and given info:

2HCl + Ba(OH)2 -----> 2H2O + BaCl2

given: 30 mL of .1M HCL

titrated w 60mL Ba(OH)2

find the molarity of Ba(OH)2 ?

now if the titrate and titrant react in a 1:1 ratio then you can use MaVa = MbVb.

but here the two do not react in a 1:1 ratio so you have to incorporate number of acidic H's and # of basic OHs represented by nA and nB respectively and use new equation nA*MaVa = nB*MbVb

my question is what is Ma and Mb. I thought that they would both be two but in the sample problem it says nA is 1 and nB is 2.
could somebody straighten this out?

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[sbdento]

Ba(OH)2 dissociates into Ba2+ and 2OH- Which gives two basic equivalents
HCL dissociates into H+ and Cl- Which gives one acidic equivalent.
There are two equivalents of the the base and one equivalent of the acid.

n=number of mole equivalents
M=molarity
V=volume

nAMaVa=nBMbVb

(1)(0.1M)(30mL)=(2)(xM)(60mL)

The volume units don't matter because they will get canceled out.

Just do some multiplication and division and voila!

ps
If you are having more problems with this stuff you might consider chad's videos. They are amazing!

 

[wizi]

considering the following rxn and given info:

2HCl + Ba(OH)2 -----> 2H2O + BaCl2

given: 30 mL of .1M HCL

titrated w 60mL Ba(OH)2

find the molarity of Ba(OH)2 ?

now if the titrate and titrant react in a 1:1 ratio then you can use MaVa = MbVb.

but here the two do not react in a 1:1 ratio so you have to incorporate number of acidic H's and # of basic OHs represented by nA and nB respectively and use new equation nA*MaVa = nB*MbVb

my question is what is Ma and Mb. I thought that they would both be two but in the sample problem it says nA is 1 and nB is 2.
could somebody straighten this out?

Ma is the molarity of H+ (a stands for acid)
Mb is the molarity of OH- (b stands for base)

 

[rmm30]

thanks very much for the help. i realized that i screwed up the question. what i meant to say in the last question was what is nA and nB (not Ma and Mb)? What i mean is becuase there are 2 mols of HCL why is nA = 1 and not 2? This came directly from chads videos.

 

[wizi]

thanks very much for the help. i realized that i screwed up the question. what i meant to say in the last question was what is nA and nB (not Ma and Mb)? What i mean is becuase there are 2 mols of HCL why is nA = 1 and not 2? This came directly from chads videos.

Because
n(a) and n (b) are NOT the coefficient #. They are numbers of ions.

HCl = 1 H+
Ba(OH)2 = 2 OH-

--> n(a) =1 and n(b) = 2

 

[rmm30]

thanks for clearing that up wiz. movin on...