2. 2
Units
Moles
• Mole (mol)
– The number of atoms needed such that the
number of grams of a substance equals the atomic
mass of the substance.
– 6.022137 × 1023
– For example, a mole of carbon-12 atoms is 12
grams, a mole of hydrogen atoms is 1 gram, a
mole of hydrogen molecules is 2 grams, etc.
4. 4
Percent
• %(weight/volume)
– Percentage of solute in a given amount of
solvent.
– Stated in grams/100ml
– Examples
• 1% solution is a solution which contains
1g/100ml.
• 10% solution is a solution which contains
10g/100ml.
Percent
• %(volume/volume)
– Percent volume of one solution in another
solution
– Examples
• A 50% ethanol solution contains 50% ethanol
and 50% water.
• A 10% ethanol solution contains 10% ethanol
and 90% water.
5. 5
Concentrated solutions (5x, 10x,
50x, 100x ……)
• Some stock solutions are concentrated and
need to be diluted before using.
• Form example, a 10X stock solution is one
that contains ten times the concentration of all
solutes relative to a working solution, which is
considered to be a 1X solution.
• Therefore, you need to dilute a 10X by a
factor of ten to obtain your final working
solution.
• Example: In order to prepare 2000ml of TAE
buffer using a 50x stock solution you need to
add 40ml of 50x TAE stock and 1960ml of
water. (1:50 dilution)
Dilutions
• Formula which is used to make working solutions
from more concentrated stock solutions.
• C1V1= C2V2
– C2= The final concentration of the working solution
– V2= Final volume of the working solution
– C1= Initial concentration of the stock solution
– V1= Amount of the stock solution required to make the
appropriate amount of the final solution
– The units must be consistent!
– Three out of four variables must be known.
6. 6
Converting
• Units can be cancelled
• You can multiply or divide anything by
one.
• Keep track of the units being used.
