SRMP Lab Skills: Molecular Biology Curriculum - American Museum ...

Science Research Mentoring Program
MOLECULAR BIOLOGY
HANDOUT: Molarity and Solutions (continued)
STOCK SOLUTIONS
When you’re working in the lab, you will often make up reactions and buffers starting with stock
solutions (not solid chemicals), which you dilute to your working concentration. Stock solutions
can be described by molarity, w/v, or v/v.
Their concentration is often described as the multiple of the working concentration: that is, a 10X
buffer needs to be diluted by a factor of 10 to get the 1x working concentration. That means if the
final volume of your reaction is 10 mL, you will use 1 mL stock solution.
To calculate dilutions you only need one formula:
(Concentration stock) X (volume of stock used) = (Concentration final) X (final volume)
But first you must convert units! The concentration of the stock must be expressed in the same
units as the concentration of the final solution. The volume used will then be expressed in the
same units as the final volume.
molecular weights
Cu(NO 3
) 2
= 187.56 g/mol
Pb(NO 3
) 2
= 331.21 g/mol
Li 2
SO 3
= 93.95 g/mol
Al 2
O 3
= 101.96 g/mol
Na 2
CO 3
= 105.99 g/mol
NaOH = 40.00 g/mol
H 2
SO 4
= 98.08 g/mol
HCl = 36.46 g/mol
Ca(OH) 2
= 74.10 g/mol
NaCl = 58.44 g/mol
H 3
PO 4
= 98.00 g/mol
KCl = 74.55 g/mol
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