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<DIV>An anhydrous chemical has NO water attached to it. A trihydrate chemical
has 3 waters attached to it.</DIV>
<DIV> </DIV>
<DIV>This becomes important when making solutions, as the weight of the water
has to be included in the weight of the compound. </DIV>
<DIV> </DIV>
<DIV>100 g of sodium acetate, trihydrate is NOT the same amount of sodium
acetate as 100 g of sodium acetate, anhydrous. Some of the weight of the sodium
acetate trihydrate is the water.</DIV>
<DIV> </DIV>
<DIV>The molecular weight of sodium acetate anhydrous is about 82. </DIV>
<DIV>(CH3COONa) = (2 Carbons x 12) + (3 Hydrogens x 1) + (2 Oxygens x 16) +
(1 Sodium x 23)</DIV>
<DIV>(You need to look at a periodic table to get the weights of the chemicals,
and the side of the container to get the formula. Often, the side of the
container also lists the molecular weight.)</DIV>
<DIV> </DIV>
<DIV>The molecular weight of sodium acetate trihydrate is about 136.</DIV>
<DIV>(CH3COONa*3H2O) = weight of the anhydrous (82) plus the weight of 6 more
hydrogens (+6) plus 3 more oxygens (+48)</DIV>
<DIV> </DIV>
<DIV>So, if the directions calls for 100 g of the anhydrous sodium acetate, but
you only have trihydrate sodium acetate, you need to set up a ratio:</DIV>
<DIV> </DIV>
<DIV>x = (136/82) x 100 = 165.8 g </DIV>
<DIV> </DIV>
<DIV>This means that 165.8 g of sodium acetate trihydrate to equal 100 g of
sodium acetate anhydrous. So to make up the solution, you would use the 165.8 g
of sodium acetate trihydrate, instead of the 100 g.</DIV>
<DIV> </DIV>
<DIV>Hope this helps.</DIV>
<DIV> </DIV>
<DIV>Peggy A. Wenk, HTL(ASCP)SLS</DIV>
<DIV>William Beaumont Hospital</DIV>
<DIV>Royal Oak, MI 48073</DIV>
<DIV> </DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=JCarpenter764@aol.com
href="mailto:JCarpenter764@aol.com">JCarpenter764@aol.com</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=histonet@lists.utsouthwestern.edu
href="mailto:histonet@lists.utsouthwestern.edu">histonet@lists.utsouthwestern.edu</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, October 27, 2003 9:32
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Histonet] (no subject)</DIV>
<DIV><BR></DIV>what is the difference between the anhydrous compound and the
trihydrate compound? </BLOCKQUOTE></BODY></HTML>