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<p><font face="serif">Gen Chem Students -- we haven't covered
solution stoichiometry yet in class (we start that Tuesday) but
that shouldn't prevent you from doing the lab writeup and prelab
for the NaOH and determination of KHP this week. Here are some
pointers to help you...</font></p>
<p><font face="serif">First -- and foremost -- the mass of KHP is
not the mass of K plus the mass of H plus the mass of P. KHP
is an abbreviation for the compound named potassium hydrogen
pthalate. Make sure you use to correct molar mass when
computing the moles of KHP used in each trial. The structure
of the compound is shown in the lab description.<br>
</font></p>
<p><font face="serif">Concentration is defined as the moles of
solute per liter of solution. Technically this is the unit "molarity".
The KHP and NaOH react on a 1:1 basis. For that reason to
find the molarity of your NaOH solution you will need to divide
the moles of KHP by the volume of NaOH used (in Liters).
Remember -- you tried to make something close to 0.13 molar --
so if you get something really different than this we may need
to talk. Anyway, compute the molarity of your NaOH for all of
your trials, and then take the average of your three GOOD
trials.<br>
</font></p>
<p><font face="serif">The formula for average deviation is found in
the description of the first lab where you measured the density
of water and that of an unknown metal. Using your three GOOD
trials compute the average deviation.</font></p>
<p><font face="serif"><b>Make sure that you record all of </b><b>this
in your lab notebook -- or somewhere that you will have access
to it</b><b> -- because you will need your determined molarity
to complete the </b><b>unknown KHP experiment you are doing
this week.</b><br>
</font></p>
<p><br>
</p>
<p>In the big box on the cover page please record the average
molarity of your NaOH solution and the average deviation in your
recorded value.</p>
<p><br>
</p>
<p>I am playing with the pre-labs, but will have the posted soon.</p>
<p><br>
</p>
<p>As always, let me know if you have questions.<br>
</p>
<p><br>
</p>
<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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