[CHM 112] Thermodynamic of Borax Lab

[Andrew J. Pounds]

On 07/27/2015 03:37 PM,  wrote:
> Dr. Pounds,
>
> I had a question on the calculation of the concentration of [B4O5(OH)4 2-] and [Na].
>
> I understand that we need to use the volume of HCl used and it's molarity, so would it be
>
> M1V1=M2V2
> V2= total volume after titration
> M2 = concentration of borax
> M1= molarity of HCl
> V1= volume of HCl
>
> And would [Na] be equal to that of borax?
>
> Thank you,

Let's make sure that we get this right.  It will really help if you look 
at the first page of the lab procedures when going through this.


For each of the \documentclass{article} \usepackage[utf8x]{inputenc} 
\usepackage[version=3]{mhchem} \pagestyle{empty} \begin{document} 
\ce{B_4O_5(OH)4$^{2-}} \end{document} you need to use 2 H+.   So the 
concentration of the \documentclass{article} 
\usepackage[utf8x]{inputenc} \usepackage[version=3]{mhchem} 
\pagestyle{empty} \begin{document} \ce{B_4O_5(OH)4$^{2-}} \end{document} 
is going to be 1/2 the moles of acid used in the titration divided by 
the original volume you collected in the test tube (5 ml)

Now, the Ksp expression is

Ksp = [Na+]^2  [B4O5(OH)4^2-] =  (2x)^2 (x).

The concentration of the \documentclass{article} 
\usepackage[utf8x]{inputenc} \usepackage[version=3]{mhchem} 
\pagestyle{empty} \begin{document} \ce{B_4O_5(OH)4$^{2-}} \end{document} 
is going to be "x".   The concentration of the Na+ is going to be 2x, 
and the value of Ksp is going to be 4x^3.

Got it?


When you prepare you plot of lnK vs 1/T, be sure to use KELVIN for the 
temperature.




-- 
Andrew J. Pounds, Ph.D.  (pounds_aj at mercer.edu)
Professor of Chemistry and Computer Science
Mercer University,  Macon, GA 31207   (478) 301-5627
http://faculty.mercer.edu/pounds_aj

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