Concentration: Molarity determining mols in a volume of solution

   

Example 2:

How many moles of solute NH3 are in 682. mL of 1.5 M NH3 solutions?

SOLUTION

Step 1

Write out the definition for molarity. M = moles solute/ liters of solution

Step 2

Tabulate the quantites given in the question and the unknown volume of solution moles of solute molarity 682 mL ? unknown 1.5 M NH3

Step 3

Convert the volume from milliliter to liters to match the molarity definition volume unit 682 mL x 1 Liter / 1000 mL = 0.682 Liters of solution

Step 4

Use the definition of molarity to cancel out volume and determine the moles of solute. mols solute = Molarity x volume in Liters moles solute = [ 1.5 mol NH3 / 1 L ][ 0.682 L / 1 ] = 1.02 moles ammonia, NH3

Dr. Walt Volland, all rights reserved 1997-2005 revised March 29, 2005