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<pre style="white-space: pre-wrap; color: rgb(0, 0, 0); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">><i> Dr. Pounds,
</i>><i>
</i>><i> I had a question on the calculation of the concentration of [B4O5(OH)4 2-] and [Na].
</i>><i>
</i>><i> I understand that we need to use the volume of HCl used and it's molarity, so would it be
</i>><i>
</i>><i> M1V1=M2V2
</i>><i> V2= total volume after titration
</i>><i> M2 = concentration of borax
</i>><i> M1= molarity of HCl
</i>><i> V1= volume of HCl
</i>><i>
</i>><i> And would [Na] be equal to that of borax?
</i>><i>
</i>><i> Thank you,
</i>
</pre>
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.
<br>
<p>
For each of the B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub><sup>2-
</sup>you need to use 2 H<sup>+</sup>. So the concentration of
the B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub><sup>2-</sup> 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 K<sub>sp</sub> expression is...</p>
<p>K<sub>sp</sub> = [Na<sup>+</sup>]<sup>2</sup>[B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub><sup>2-</sup>]
= (2x)<sup>2</sup> (x) <br>
</p>
<p>The concentration of the B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub><sup>2-
</sup>is going to be "x". The concentration of the Na<sup>+</sup>
is going to be "2x", and the value of K<sub>sp</sub> = 4x<sup>3</sup>.</p>
<p>Got it?</p>
<p><br>
</p>
<p>Then prepare a plot of ln(K<sub>sp</sub>) vs. 1/T. Be sure to
use Kelvin for the temperature. From the equation</p>
<p><img alt="$\ln(K) = (−\Delta H^{\circ}/R)(1/T) + \Delta
S^{\circ}/R$" style="vertical-align: middle;"
src="cid:part1.7E7DAAAA.03BE90EB@mercer.edu"></p>
<p>You can determine the value of <img alt="$\Delta H^{\circ}$"
style="vertical-align: middle;"
src="cid:part2.E39F2A94.2CAC6ED7@mercer.edu"> from the slope and
<img alt="$\Delta S^{\circ}$" style="vertical-align: middle;"
src="cid:part3.35933D83.EDD11360@mercer.edu"> from the
y-intercept.</p>
<br class="Apple-interchange-newline">
<pre class="moz-signature" cols="72">--
Andrew J. Pounds, Ph.D. (<a class="moz-txt-link-abbreviated" href="mailto:pounds_aj@mercer.edu">pounds_aj@mercer.edu</a>)
Professor of Chemistry and Computer Science
Director of the Computational Science Program
Mercer University, Macon, GA 31207 (478) 301-5627
</pre>
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