Wednesday, January 5, 2011

Molarity - Isabelle Cheng January 5, 2011

Isabelle Cheng
January 5, 2011
Block 2-2 Chem 11
Ms. Chen


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
                        3.0 L

= 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
1                           10^3

= 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
                                    36.5 g

V = 3.57 X10^-3 mol = 1.14 L
       2.40 mol/L

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