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<div class="moz-cite-prefix">On 10/26/14 15:19, wrote:<br>
</div>
<blockquote
cite="mid:C40B2F181831EF44A88CD73525827803130CFB7803@MERCERMAIL.MercerU.local"
type="cite">
<div dir="ltr">Hi Dr. Pounds!
<div>I'm trying to do the lab, and we either really messed up in
lab or I'm calculating the deltaH values for reactions three
and four wrong. I think my mistake might be in calculating the
mass of the solution for these reactions. Could you give me
any pointers for calculating the mass of the solution for
reactions three and four?</div>
<div>Thanks! <br clear="all">
<div> <br>
</div>
</div>
</div>
</blockquote>
<br>
<font face="serif">So, in the equation <img style="vertical-align:
middle" src="cid:part1.04000908.09020907@mercer.edu" alt="$q = m
c_s \Delta T$"> you need to use the mass of the solution. You
know the volume and the density of the solution is listed on the
lab report form. You can therefore use <img
style="vertical-align: middle"
src="cid:part2.06040906.08020804@mercer.edu" alt="$m = \rho V$">
to compute the mass of the solutions. The specific heats for
these solutions can also be found on the report form.<br>
<br>
Now, when it comes to <img style="vertical-align: middle"
src="cid:part3.08050903.05010001@mercer.edu" alt="$\Delta H$">,
you have to remember that it is the constant volume heat capacity
on a per mole basis. So take your <img style="vertical-align:
middle" src="cid:part4.02050203.05020806@mercer.edu" alt="$q$">
that you determined and divide it by the moles of substance.<br>
<br>
In the case of the dissolution of NaOH you have roughly 2 grams of
NaOH. Convert this to moles (2 g / 40 g/mol) = 0.05. So your
enthalpy of reaction for the dissolution of NaOH should be <img
style="vertical-align: middle"
src="cid:part5.09020608.00090400@mercer.edu" alt="$q / 0.05$">.<br>
<br>
In the case of the reaction of NaOH (aq) with HCl (aq) you have 50
ml of 1 M NaOH (that would also be 0.05 moles), so divide the heat
by that amount to get the enthalpy like you did before.<br>
<br>
Hopefully that give you enought to get through the rest of the
lab, but let me know if you have any questions.<br>
<br>
<br>
<br>
<br>
</font><br>
<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
Mercer University, Macon, GA 31207 (478) 301-5627
<a class="moz-txt-link-freetext" href="http://faculty.mercer.edu/pounds_aj">http://faculty.mercer.edu/pounds_aj</a>
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