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<div class="moz-cite-prefix">On 07/20/14 17:52, wrote:<br>
</div>
<blockquote
cite="mid:C40B2F181831EF44A88CD73525827803130774D8FA@MERCERMAIL.MercerU.local"
type="cite">
<pre wrap="">Dr. Pounds,
On the additional problems for chapter 16 number 5, why did you square 6.31x10^-5? I built the ICE table and I just can’t figure out why that concentration is squared?
Thank you</pre>
</blockquote>
<font face="serif">Since the concentration of the conjugate acid is
equal to the concentration of hydroxide ( every codeine molecule
that ionizes and reacts with water forms C<sub>18</sub>H<sub>21</sub>NHO<sub>3</sub><sup>+</sup>
and OH<sup>-</sup> ) we can think of the expression for Kb as<br>
<br>
Kb = ( [</font><font face="serif"><font face="serif">C<sub>18</sub>H<sub>21</sub>NHO<sub>3</sub><sup>+</sup></font>]
[ </font><font face="serif"><font face="serif">OH<sup>-</sup></font>
]) / [</font><font face="serif"><font face="serif"><font
face="serif">C<sub>18</sub>H<sub>21</sub>NO<sub>3</sub></font></font>
]<br>
<br>
Kb = </font><font face="serif"><font face="serif">( (x)</font><font
face="serif"> (x)</font><font face="serif">) / ([</font><font
face="serif"><font face="serif"><font face="serif">C<sub>18</sub>H<sub>21</sub>NO<sub>3</sub></font></font>
] - x)<br>
<br>
Kb = x<sup>2</sup> / </font></font><font face="serif"><font
face="serif"><font face="serif"><font face="serif">([</font><font
face="serif"><font face="serif"><font face="serif">C<sub>18</sub>H<sub>21</sub>NO<sub>3</sub></font></font>
] - x)</font></font> <br>
<br>
Since x is negligible, this reduces to...<br>
<br>
</font></font><br>
<font face="serif"><font face="serif"><font face="serif"><font
face="serif">Kb = x<sup>2</sup> / </font></font><font
face="serif"><font face="serif"><font face="serif"><font
face="serif">([</font><font face="serif"><font
face="serif"><font face="serif">C<sub>18</sub>H<sub>21</sub>NO<sub>3</sub></font></font>
])<br>
<br>
<br>
</font></font></font></font></font>Since the [OH<sup>-</sup>]
is equal to x, and I know the concentration of codeine, I can
solve for Kb as show in the online solution.<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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