Molar Concentration or Molarity


Molar concentration:
-A homogeneous mixture where one substance is dissolved is called a solution
-In salt water salt is the solute and water is the solvent

We need to be able to calculate the concentration of solutions.  The concentration is the amount of the solute dissolved in a certain bolume of a solution.

Molar concentration or molarity is the number of moles in one lire of a solution.  We use "M" to denote concentration and it has the units of "moles/L".

Formuale:
                 Moles of solute (mol) 
Molarity = volume of solution (L)   or simply M= mol
                                                                            L

Ex. Calculate the number of grams of calcium hydroxide in 1.30 L of a 0.75 M Ca(OH)2 solution.
Moles of Ca(OH)2 = 0.75 M x 1.30 L = 0.975 mol/L of Ca(OH)2

Ex. How many moles of KCI are contained in 0.25 L of 0.80 mol/L KCI?
moles of KCI = molarity x volume = 0.80 mol/L KCI x 0.25 L
=0.20 mol/L

Ex. How many grams of MgCl2 are contained in 30.0 mL of 1.5 x 10^2 mol/L MgCl2?
moles of MgCl2 = 1.5 x 10^2 mol/L MgCl2 x .0300 L = 4.5 x 10^4 mole of MgCl2

Ex. Calculate the volume in mL of a 0.450 M NaCl solution that contains 96.45 g NaCl.

MMass= 23.0 + 35.5 = 58.5 g/mol
L = mol
        L

moles of NaCl= 96.45 g = 1.64871 moles of NaCl2
                         58.5 g

1.64871 = 3.6638 L and since we need it in mL, the answer is 3663.8 mL
0.450

Here is a video explaining how to calculate molarity:

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