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Topic: Titration Balancing equation  (Read 3472 times)

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Offline islamike

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Titration Balancing equation
« on: October 31, 2015, 08:34:49 PM »
Hi everyone,

I don't really know if I am doing this question right:

2.954g of a dicarboxylic acid Q was dissolved into 500cm3 of solution. A portion of 25.0cm3 of the solution was then taken and required 27.3cm3 of sodium hydroxide solution at 0.104moldm3. Determine the formula of the dicarboxylic acid Q.

I used this balanced equation: C2H2O4 + 2NaOH  :rarrow: NaC2O4 + 2H3O

and calculated the Mr of C2H2O4 to be 104.043. Dividing this answer by the Mr(C2H2O4) gives me 1.156....
Now I am not sure if this is correct.

Could someone please verify that the balanced equation is correct and that the Mr I obtained is correct for this question.
Any help is appreciated

Thanks in advance.

Offline thetada

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Re: Titration Balancing equation
« Reply #1 on: November 01, 2015, 02:31:39 AM »
Hi there, welcome to the forum. Before you think about the relative mass of the acid, you need to start by working out the number of moles. To work out the equation, which you very sensibly considered, you can let the formula of the acid be H2X, where X is the dicarboxylate.

Offline Borek

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Re: Titration Balancing equation
« Reply #2 on: November 01, 2015, 02:59:16 AM »
You are doing strange things (and using C2H2O4 as a formula doesn't help, as thedata wrote, using symbolic formula of H2X would be much better, or - taking into account fact the infomation given - X(COOH)2).

However, 104.0 g/mol is a correct molar mass of the acid. Now, assuming the formula to be X(COOH)2), how many grams per "mole of X"?
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Offline thetada

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Re: Titration Balancing equation
« Reply #3 on: November 01, 2015, 03:04:35 AM »
Sorry, you were further ahead in the calculation than I realised. Thanks Borek

Offline islamike

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Re: Titration Balancing equation
« Reply #4 on: November 01, 2015, 08:37:23 AM »
You are doing strange things (and using C2H2O4 as a formula doesn't help, as thedata wrote, using symbolic formula of H2X would be much better, or - taking into account fact the infomation given - X(COOH)2).

However, 104.0 g/mol is a correct molar mass of the acid. Now, assuming the formula to be X(COOH)2), how many grams per "mole of X"?

So, the gmol-1 of X(COOH)2 104? In this case I need to take 94 gmol-1 of (COOH)2 away from 104, which is 10.  But what does X represents here? an element, Beryllium or Boron? or perhaps 10H (Hydrogen)?

Offline thetada

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Re: Titration Balancing equation
« Reply #5 on: November 01, 2015, 09:06:36 AM »
I'm not sure if your calculation of 94g mol-1 is correct. The leftover should be composed of carbon and hydrogen atoms.

Offline islamike

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Re: Titration Balancing equation
« Reply #6 on: November 01, 2015, 09:33:32 AM »
I'm not sure if your calculation of 94g mol-1 is correct. The leftover should be composed of carbon and hydrogen atoms.

Sorry my bad, 94gmol-1 should be 90gmol-1.

So, the final formula is H2C(COOH)2 ?
I think that makes sense.

Thank you both. Much appreciated

Offline islamike

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Re: Titration Balancing equation
« Reply #7 on: November 01, 2015, 10:05:03 AM »
Wondering what will be the balanced equation?

Since my furmula, C2H2O4 , was wrong and working out that the dicarboxylic acid now has the formula H2C(COOH)2, the balanced equation: C2H2O4 + 2NaOH  :rarrow: NaC2O4 + 2H3O is wrong.

Looking at my work, I am confused how I obtained 104.043, since my equation wasn't balanced. What balanced equation should I have used

and what is the balanced equation after finding that dicarboxylic acid has formula C3H4O4 ?

Offline thetada

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Re: Titration Balancing equation
« Reply #8 on: November 01, 2015, 10:27:11 AM »
Your equation was wrong but it still had the correct Stoichiometry, namely 1 Mole of acid to 2 moles of alkali. Questions like this are common ( at least in UK A- level) the trick is to let acid be H2X and base the Stoichiometry on the number of protons available from the acid and the number of hydroxide ions on the base, which is effectively what you did

Offline islamike

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Re: Titration Balancing equation
« Reply #9 on: November 01, 2015, 11:08:50 AM »
Thanks Thedata,

your help is appreciate  :)

Offline thetada

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Re: Titration Balancing equation
« Reply #10 on: November 01, 2015, 11:23:45 AM »
My pleasure :-)

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