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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Lindsay on October 28, 2008, 09:23:15 PM

Title: What is the molar concentration of NaOH solution
Post by: Lindsay on October 28, 2008, 09:23:15 PM
Problem 1

This one I'm not too sure about. Actually, I'm not too sure on the balanced equation. I can figure out the rest but the equation got me stuck. Please help

Oxalic acid, H2C2O4•2H2O - 126.07 g/mol is often used as a primary standard for the standardization of a NaOH solution. If 0.147 g of oxalic acid dihydrate is neutralized by 23.64 mL of a NaOH solution, what is the molar concentration of the NaOH solution? Oxalic acid is a diprotic acid. (Hint: what is the balanced equation?)

I think this is the wrong balanced equation
H2C2O4•2H2O + 2NaOH ---- 2NaC2O4•2H2O + H2O

0.147g/126.07g/mole - 0.00117 mole (oxalic acid)

Appreciate any help
Title: Re: What is the molar concentration of NaOH solution
Post by: Astrokel on October 29, 2008, 01:06:09 AM
Quote
H2C2O4•2H2O + 2NaOH ---- 2NaC2O4•2H2O + H2O
Oxalic acid is diprotic!
Title: Re: What is the molar concentration of NaOH solution
Post by: Lindsay on October 29, 2008, 10:42:50 AM
Meaning it has two Hydrogen Ions that can completely dissociate, right?

Is the equation like this

H2C2O4•H2O + NaOH ---- NaHC2O4•H2O + H2O

Thanks

Lindsay
Title: Re: What is the molar concentration of NaOH solution
Post by: macman104 on October 29, 2008, 10:47:39 AM
No, your base equation was correct, but it was not balanced (count your hydrogens).  Also, I don't know about this, but maybe someone else will, but will the oxalic acid still be a dihydrate after the reaction?
Title: Re: What is the molar concentration of NaOH solution
Post by: Arkcon on October 29, 2008, 10:57:53 AM
Generally, in solution, a hydrate's water molecules are assumed to be, well, not gone, not really dissociated or ionized, but well, not considered.  Of course, the original poster can't just ignore them, they are there, when the dry solid is massed out, but usually, when the reaction is written, we assume they don't participate.
Title: Re: What is the molar concentration of NaOH solution
Post by: Astrokel on October 29, 2008, 11:11:28 AM
Quote
No, your base equation was correct, but it was not balanced (count your hydrogens).
I thought it was wrong because it should be Na2C2O4.2H2O?
.
Title: Re: What is the molar concentration of NaOH solution
Post by: macman104 on October 29, 2008, 11:58:32 AM
OH!  I didn't even look at that, lol, I saw the Na and was done, lol.  Fair enough about the hydrate, I wasn't sure if you dissociate them or leave them with the molecule.