<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<div class="moz-cite-prefix">On 04/14/2013 04:29 PM, wrote:<br>
</div>
<blockquote
cite="mid:C40B2F181831EF44A88CD7352582780301E53DB3EF@MERCERMAIL.MercerU.local"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<style type="text/css" id="owaParaStyle"><!----></style>
<div style="direction: ltr;font-family: Tahoma;color:
#000000;font-size: 10pt;">On chapter 16, question 104, the
equation set up was F- + H2O --> OH- + HF. Why is it not HF
--> H+ + F-?
<div><br>
</div>
<div>"What is the pH of 0.082M NaF, Ka for HF is 7.1E-11."</div>
</div>
</blockquote>
<br>
Because you were only given a compound (NaF) that contained the
conjugate base (F-) of the Weak acid (HF). There is no HF initially
in the solution -- you form it as a result of the system
establishing equilibrium. <br>
<br>
<br>
In this type of "hydrolysis" problem you write the equilibrium so
that you make OH- and the weak acid HF. This also requires that you
modify the Ka value and convert it to a Kb.<br>
<br>
<br>
<pre class="moz-signature" cols="72">--
Andrew J. Pounds, Ph.D. (<a class="moz-txt-link-abbreviated" href="mailto:pounds@theochem.mercer.edu">pounds@theochem.mercer.edu</a>)
Associate Professor of Chemistry and Computer Science
Mercer University, Macon, GA 31207 (478) 301-5627
</pre>
</body>
</html>