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Topic: Titration doubt  (Read 10673 times)

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Offline xstrae

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Titration doubt
« on: June 22, 2006, 11:46:28 AM »
25ml of a solution of Ba(OH)2 on titration with 0.1 molar solution of HCL gave a titre value of 35ml. What is the molarity of Ba(OH)2 ?

Here is my work:
N1V1=N2V2

25N=0.1*35
N=0.14
Normality = n x molarity
0.14 = 2 x molarity
so molarity = 0.07
is this right?? because my book answer says it is 0.14


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Offline tamim83

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Re: Titration doubt
« Reply #1 on: June 22, 2006, 11:57:12 AM »
Quote from: konichiwa2x on June 22, 2006, 11:46:28 AM
25ml of a solution of Ba(OH)2 on titration with 0.1 molar solution of HCL gave a titre value of 35ml. What is the molarity of Ba(OH)2 ?

Here is my work:
N1V1=N2V2

25N=0.1*35
N=0.14
Normality = n x molarity
0.14 = 2 x molarity
so molarity = 0.07
is this right?? because my book answer says it is 0.14




I think you need to use the equation

M1V1=M2V2 where M is the molarity.  You do not need to "convert" from normality to molarity, your "N=1.4M" answer is the correct one. 
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Offline Stewed_ant

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Re: Titration doubt
« Reply #2 on: June 22, 2006, 12:01:19 PM »
This is a job for the girl from the titration competition!!!

 the best fun i ever had   :-[

note Concentration = molarity?

Ba(OH)2 + 2HCL -> 2H20 + Ba+ +2CL-

Concentration(HCL) =0.1 molar
Volume (HCL) = 35 m = 0.035 L
moles (HCL) = 0.0035
Moles of Ba(OH)2 = 1/2 * moles(HCL) = 0.00175
Volume Ba(OH)2 = 25 ml = 0.025 L
Concentration Ba(OH)2 = moles/volume = 0.00175/0.025 = 0.07

I think your right, if molarity = concentration. Which i'm almost 100% (99.999%) certain it is.

I think the book ignored the fact that the equation states that there is half as much  Ba(OH)2 as ther eis HCL,  that would give them the answer they got which is twice that of the correct. If i was you i would burn that book or atleast loudly complain.

Looks like we may have a difference of opinion Tamim83, where did you get that equation from?
« Last Edit: June 22, 2006, 12:07:39 PM by Stewed_ant »
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Offline xstrae

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Re: Titration doubt
« Reply #3 on: June 22, 2006, 12:07:07 PM »
oh great now which one is right? anyway thanks stewed. tamim, i think your eq is incorrect. doesnt the number of moles come into play in your equation if u bring in molarity? anyway i think its easier to calculate with normality.
and molarity = concentration.

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Offline Stewed_ant

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Re: Titration doubt
« Reply #4 on: June 22, 2006, 12:09:23 PM »
My calculation is 100% correct, titration is my thing ;) and my way is the best way to do it for me anyway, if your more comfortable doing it your way, that's cool to. ;)

either way, we both got it right.
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Offline Stewed_ant

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Re: Titration doubt
« Reply #5 on: June 22, 2006, 12:40:36 PM »
sorry if i got catty tammim  :-\

i feel guilty
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Offline tamim83

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Re: Titration doubt
« Reply #6 on: June 22, 2006, 02:23:24 PM »
OK, I suppose I need to fully explain myself here

Barium Hydroxide is a strong base.  So the ionic equation is

Ba2+ + 2OH- + 2H+ + 2Cl  ---> Ba2+ + 2Cl- +2 H20

The net ionic equation is then

2OH- + 2H+ ---> 2H2O

Which since all of the coeficiencts are the same is

H+ + OH- ---> H2O

Which gives you the correct stoichiometry here

Now, the moles of H+ used is the same as the moles of HCl used in your tittration, which is, as calculated by stewed_ant is 0.0035mol.  This is equal to the moles of OH- neutralized.  So the molarity of the OH- is 0.14M, which agrees with the book. 

Now here is the thing.  That is the molarity of the OH- in solution, not molarity of Ba(OH)2.   Using stoichiometry, the molarity of Barium hydroxide is half of the molarity of OH-, which is, as Stewed_Ant calculated is 0.07M. So what you should do konichiwa2x is check what the book is asking for.  Is it molarity of hydroxide or molarity of barium hydroxide, which are two different values.  The answer in the book is for molarity of hydroxide ions not barium hydroxide.  So it is the book's mistake not mine.  I merely calculated the molarity of hydroxide ions.  So please read your question again to se what is being asked exactly.  It is not unusual for the book to mix things up  ;) 

Stewed_ant, you were right for the question that konichiwa2x posted.  I was merely trying to diagnose the desceptancies in answers here.  My equation is the well used dilution equation that can be used for 1:1 stoichiometry instances (like a lot of acid-base neutraliztions).  I know, after five years of chemistry (I am a grad. student) I have used it a million times, I am surprised you never seen it. 

Cheers to you both  ;D
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Offline xstrae

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Re: Titration doubt
« Reply #7 on: June 23, 2006, 12:35:10 PM »
ok thanks tamim and stewed. looks like we all were correct after all.  ;)
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Offline tamim83

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Re: Titration doubt
« Reply #8 on: June 23, 2006, 01:03:24 PM »
Quote from: konichiwa2x on June 23, 2006, 12:35:10 PM
ok thanks tamim and stewed. looks like we all were correct after all. ;)

No problem.   ;) Just curious though, since I am interested in chemistry curricula and such, what did the question say exactly and what book are you using? 
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Offline xstrae

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Re: Titration doubt
« Reply #9 on: June 24, 2006, 01:07:48 PM »
I dont remeber the exact question. I just happened to come over it while browsing in a library. Anyway, the book is IIT:Chemistry (its an Indian book. you definitely wouldn't have heard of it.
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Offline Stewed_ant

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Re: Titration doubt
« Reply #10 on: July 31, 2006, 10:37:47 AM »
eh ;)

i had such a good teacher he taught us to work things out intuetively, i suppose that's why i never had the need for an equation.
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