Notesale: Turn your study into money

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Solution Making
Some general guidelines to follow when making solutions
1
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2
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80%) needed
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The
solution will be brought up to the final volume after the pH is adjusted
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Know the pKa of the buffer being used
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The values can be obtained
from the Merck Index, Sigma Chemical Catalog, and on-line
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How
quickly the pH changes will depend upon the concentration of the buffer and how close
the pH of the solution is to the pKa value
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4
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Measure final volumes with
graduated cylinders; never use the gradations on beakers and flasks, since these are
notoriously inaccurate
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Any solutions containing proteins,
carbohydrates or other labile components must be refrigerated
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millimolar (mM) vs
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You will need to use these skills this semester
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You need to be comfortable interchanging these
units
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02 M / 20 mM NaCl / 2 x 104 μM = 2 x 107 nM
There are practice problems dealing with units interconversions at the end of this section
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Units of “%(w/v)” (ie
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Thus, given a final concentration of a chemical (assuming you are starting
with a pure, dry substance) and the required final volume,
gram of the chemical = Final volume (ml) x fractional weight
For example: to prepare 200 ml of 5% NaCl: 200 x 0
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This would be prepared by dissolving 5g of NaCl in approximately 150 ml of water, and then
bring the final volume up to 200 ml in a graduated cylinder
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e
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Thus, given a final concentration of a liquid
chemical (assuming you are starting with a pure, 100%, substance) and the required final
volume,
volume of the liquid chemical = Final volume (ml) x fractional volume diluent
For example, to prepare 200 ml of 70% ethanol: 200 x 0
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This would be prepared by adding 140 ml of ethanol to a graduated cylinder and then adding
water to a final volume of 200 ml
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The easiest way to calculate the necessary dilutions is to use the following relationship:
V1 x C1 = V2 x C2
V equals the volume
C equals the concentration
MWs of Some Molecules
Sucrose (MW = 342)
Glycine (MW: use Google)
NaCl (MW = 58)
KCl (MW = 74

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