The more solute there is per unit of solution, the more concentrated the solution is.
The most convenient method for measuring concentration is molarity. Molarity is a measure of how many
moles of solute are dissolved in 1 liter of solution.
A solution in which 5 moles of solute are dissolved in 1 liter of solution has a concentration of
5 moles/liter which we will abbreviate 5 M, and we say it is 5 Molar solution.
Molarity is a conversion factor between volume and moles, which allows us to determine the amount of
solute (in grams or moles) based on the easily measured volume of the solution.
If a solution has a concentration of 1 M this means that
Similarly, in a solution with a 0.2 M concentration
Just remember that Molarity is
moles
Liter
1 liter solution = 1 mole solute
1 liter solution = 0.2 moles solute
and use it as any other conversion factor
Examples:
a)
How many moles of NaCl are there in 2.5 liters of a 0.2 M solution?
(hint: start with the amount, not the concentration)
2.5 liters  0.2 moles NaCl = 0.5 moles
1 liter
b)
If you want to make a 5 M solution of LiOH in a 500 ml volumetric flask, how many
grams of LiOH would you need to dissolve?
500ml  1 liter
 5 moles

23.95 g
= 59.88 g
1000 ml
1 liter
1 mole LiOH
d)
How many milliliters of 6 M LiOH solution would you need if you wanted 100 g of
solute?
100 g 
1 mole LiOH
 1 liter
 1000 ml
= 695.9 ml
23.95 g
6 moles
1 liter
Molarity is measure the concentration of a solution. A 1 Molar solution has 1 mole of substance dissolved
in 1 liter of solution. The abbreviation for molarity is M, so a 5 M solution of NaCl has a concentration of
5 moles per liter
Note: you don’t make a 1 M solution by adding 1 mole of substance to 1 liter of water.
You make a 1 M solution by taking 1 mole of substance and adding enough water so that when the
substance is dissolved the solution has a volume of 1 liter.
In order to dilute a solution from one molarity to another, start with the amount of solution you want to
end up with, then multiply a fraction that has the desired concentration in the numerator and the higher
concentration in the denominator. In other words, multiply by “what you want over what you’ve got.”
a) How many ml of 6.0 M NaF solution would you need in order to make 500 ml of a 2.5 M solution?
The result above means that you would add 208 ml of the 6M solution, then add water until you had 500 ml