1. Concentration Expressed in molarity, e.g.: 2 M NaCl = 2 “molar” NaCl
= 2 moles NaCl per liter of solution
(where 1 mole = x 1023 molecules)

2. How to make a 2M NaCl stock solution
You will have to put 2 moles of NaCl inside 1 liter of solution
From the Periodic Table, 1 mole of NaCl weighs:
1 x Na = grams,
1 x Cl = grams
1 x NaCl = = grams
So the formula weight of NaCl = grams
In a beaker, slowly dissolve 2 x = grams NaCl into about 800 ml water, then pour into graduated cylinder and make volume up to exactly 1 liter (=1000 ml)

3. Algebra Reminder
Whatever you do on one side of the equal sign, you must also do on the other side of the equal sign: = = =

4. How to make 200 ml of a 2 M NaCl stock solution
2 M NaCl = g / liter
= g /1000 ml
But we don’t want 1000 ml, we want 200 ml!
Use algebra: g = x g
1000 ml ml
Now multiply by 200 ml on both sides to find x:
( g)(200 ml) = (x g)(200 ml) = x = g
(1000 ml) (200 ml)
(So you will add 23.38g NaCl into a total of 200ml)

5. How to use stock solutions
How would you make 150 ml of a 1M NaCl solution from a 3M NaCl stock solution?
In other words, how many ml of your stock solution must go into 150 ml?
C1V1 = C2V2
(x ml)(3M) = (150 ml)(1M)
Now divide both sides by 3M to find x:
(x ml)(3M) = x ml = (150 ml)(1M) = 50 ml
(3M) (3M)

6. Fold Dilutions Most common notation, e.g. for a 10-fold dilution:
1 : 10
= 1 part (stock solution) into a total of parts
= 1 part (stock solution) + 9 parts (water)

7. A B C Serial Dilutions Bob's.ppt
transferring
1 ml 1 ml
A = concentrated stock solution
+9 ml +9 ml B = 1:10 dilution of A
C = 1:10 dilution of B and
a 1: dilution of A
Bob's.ppt
Graphics by Bob A B C