January 5, 2011
Block 2-2 Chem 11
Molarity is the number of moles of the substance contained in 1 Liter of solution. This is based on a substance in a solution. Also the other name for Molarity is called Molar Concentration.
There is a difference between concentration, concentrated, and dilute. The concentration of a substance in a solution is the quantity of the substance, which is in a given volume of the solution. The concentrated solution has a high concentration. This means that a lot of the substance is dissolved in the solution. Dilute solution has a low concentration which means that very little of the substance is dissolved.
Here is the Formula:
Molarity/ Molar Concentration = moles
Or this way might be easier to remember:
M = mol
That means if you want to solve for L it would be:
L = mol
That means if you want to solve for mol it would be:
Mol = M X L
Here is an example:
If 3.0 L of solution contain 5.0 mol of CaCl, what is the molarity of the CaCl?
Molarity = 5.0 mol = 1.666666667
= 1.6 mol
Let’s try something harder now! ~
This time you have to convert mL into Liters for the equation to work!
40.0 mL of a solution contains 0.060 mole of CaCl?
40.0mL X 1 L
= 0.0400 L
Molarity = 0.060
= 1.5 M CaCl
The next example is determining the number of moles:
What is the mass of NaCl is contained in 4.00L of 0.300 M NaCl?
Moles of NaCl = 0.300 X 4.00 = 1.2 mol
Mass of NaCl = 1.2mol X 58.5g = 70.2 g
The next example is determining the volume.
What is the volume of 2.40 M HCl can be made from 100.0 g of HCl?
Moles HCl = 100.0 g X 1mol = 2.74 mol
V = 3.57 X10^-3 mol = 1.14 L