Molar Concentration or Molarity
-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".
Moles of solute (mol)
Molarity = volume of solution (L) or simply M= mol
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
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
moles of NaCl= 96.45 g = 1.64871 moles of NaCl2
1.64871 = 3.6638 L and since we need it in mL, the answer is 3663.8 mL
Here is a video explaining how to calculate molarity:
Posted by TheChemGuys