Molarity
- Molarity (M) is the amount of a substance in a certain volume of solution. Molarity
is defined as the moles of a solute per liters of a solution. Molarity is also known
as the molar concentration of a solution.
Formula
- To calculate the molarity of a solution, you divide the moles of solute by
the volume of the solution expressed in liters.
Example Problems:
1. Calculate the molarity of a 3 L solution prepared by dissolving 20 moles of
glucose in enough water.
Step 1: Identify what is required in the problem.
Calculate the molarity in the problem.
Step 2: Identify the given in the problem
Moles of solute: 20 moles
Solution (L): 3 L
Step 3: Write the working equation.
M = nsolute = mol solute
m
solvent kg solvent
Step 4: Substitute the given values
M = 20 mols
3L
Step 5: Find the answer.
M = 6.67 M
2. What is the molarity of a 0.30 L solution containing 0.50 moles of NaCl?
Step 1: Identify what is required in the problem:
Calculate the molarity of the solution
Step 2: Identify the given in the problem.
Moles of solute: 0.50 moles
Solution (L): 0.30 L
Step 3: Write the working equation.
M = nsolute = mol solute
m
solvent kg solvent
Step 4: Substitute the given values.
M = 0.50 mols
0.30 L
Step 5: Find the answer
M = 1.67 M
3. 0.444 mol of CoCl2 in 0.654 L of solution. What is the molarity in the
solution?
Step 1: Identify what is required in the probem.
Calculate the molarity of the solution
Step 2: Identify the given in the problem.
Moles of solute: 0.444 moles of CoCl2
Solutio (L): 0.654 L
Step 3: Write the working equation.
M = nsolute = mol solute
m
solvent kg solvent
Step 4: Substitute the given values.
M = 0.444 mols
0.654 L
Step 5: Find the answer.
M = 0.679 M
4. 1.457 mol KCl in 1.500 L of solution. Calculate the molarity in the solution.
Step 1: Identify what is required in the problem.
Calculate the molarity of the solution.
Step 2: Identify the given in the problem.
Moles of Solute: 1.457 moles of KCl
Solution (L): 1.500 L
Step 3: Write the working equation.
M = nsolute = mol solute
m
solvent kg solvent
Step 4: Substitute the given values.
M = 1.457 mols
1.500 L
Step 5: Find the answer.
M = 0.971 M
5. 0.25 moles of NaCl in 0.3 L of solution. What is the molarity in the
solution?
Step 1: Identify what is required in the problem.
Calculate the molarity of the solution
Step 2: Identify the given in the problem.
Moles of Solute: 0.25 moles of NaCl
Solution (L): 0.3 L
Step 3: Write the working equation.
M = nsolute = mol solute
m
solvent kg solvent
Step 4: Substitute the given values.
M = 0.25 mols
0.3 L
Step 5: Find the answer.
M = 0.83 M
