<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
span.EmailStyle18
{mso-style-type:personal-compose;
font-family:"Arial",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;
font-family:"Calibri",sans-serif;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="#0563C1" vlink="#954F72" style="word-wrap:break-word">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">I got a number of people asking questions dealing with conc. units and<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">conversions between those units after the quiz. Part of the problem was<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">people having trouble remembering what those units are. Without this<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">knowledge you’ll have trouble doing certain things. These units can be<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">used as conversion factors in problems. Also, if you don't know the units<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">themselves it’s impossible to do any of these problems. These units are<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">given at the end of the chapter in the "Key Equations" list.<br>
<br>
One other thing I noticed was people having problems with density, sometimes<br>
not knowing exactly what it was but more often confusing density of solution<br>
with density of solvent. You need to read the question carefully as it will tell<br>
you whether it's the density of the solvent, solute or solution. That can often<br>
be a hint as to what you have to do. A number of people missed the conc.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">conversion problems. Since I can’t see the work for the quiz I’m not sure<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">why but often it’s because people don’t know the units themselves.<br>
<br>
You need to memorize the following conc. units if you haven't already. Treat<br>
this like you did spelling words back in grade school. I know you can have an<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">information sheet for the quizzes and exams (and the textbook) but that won’t<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">help if you don’t really understand them.<br>
<br>
mass %: (mass solute)/(mass soln) * 100 <br>
or think of it as <b>part per hundred</b> (<b>pph</b>)<br>
ex. 10% sugar ==> (10 g sugar)/(100 g soln)<br>
<br>
units don't have to be "g", just same unit for numerator and denom.<br>
<br>
mass soln = mass solute + mass solvent<br>
(needed when converting from or to molarity, as is density of soln)<br>
<br>
ppm: like pph (mass solute)/(mass soln) * 10^6<br>
or (g solute)/(10^6 g soln) <br>
<br>
ppb: (mass solute)/(mass soln) * 10^9<br>
or (g solute)/(10^9 g soln)<br>
<br>
M: molarity (mol solute)/(L soln) denominator is vol of soln<br>
<br>
<i>m</i>: molality (mol solute)/(kg solvent) denominator is solvent only (not soln)<br>
<br>
X: mol fraction (mol solute)/(total mol soln)<br>
total mol soln = (mol solute + mol solvent)<br>
<br>
mol % = X * 100<br>
<br>
mole fractions add to 1, mole percents add to 100<br>
<br>
solubility: (g solute)/(100 g solvent) denominator is <b>solvent only</b> (not soln)<br>
<br>
can be obtained by doing: (g solute/g solvent) * 100 g solvent<br>
<br>
Do NOT confuse this with mass %.<br>
For mass % the denominator is mass of SOLUTION<br>
<br>
For solubility the denominator is mass of SOLVENT<br>
<br>
In terms of converting between the units I suggest you try doing them the way I<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">did in class. While there are other ways of doing them I’ve provided a single<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">road map on how to do all of them. It’s easier to learn one way to approach all<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">these problems than several different ways based on what your given and what<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">you’re after.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Hope this helps.<br>
<br>
Dr. Zellmer<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
</div>
</body>
</html>