A chemistry teacher who teaches General Chemistry at the K-12 level..
Molarity, an expression of concentration is expressed as a ratio of moles of solute to volume of solution in Litres or dm^3.
Molarity calculations are important in all stages of learning -from High School Chemistry to Graduate research.
Molarity is one of the popular ways in which concentration of a solute is expressed.
Every binary solution has two components- solute and solvent. When the solute is expressed as the number of moles and the solution used is expressed in units of Litres or dm^3 then it is termed as molarity.
This introductory article gives you the basic calculations you will encounter in preparing molar solutions or solving numericals based on molarity.
We use M or mol/L as unit for molarity.
1 Liter = 1000 mL.
The General format for solving any numerical problem must include
- The information given to you in the problem along with the appropriate units
- You must then write the formula that you will use to solve the numerical
- At times you will have to modify the formula suited to the needs of the problem
- Then, substitute the given values in your formula
- Finally, calculate and give the final answer with appropriate units
Types of problems to calculate molarity
1. Type 1
Problems where you are directly asked to calculate the molarity
What is the molarity of a 0.30 liter solution containing 0.50 moles of NaCl?
Moles of NaCl= 0.5 mol
Volume of solution= 0.3L
Substitution: M= 0.5mol/0.3L
Final answer= 1.67 M
2. Type 2
Problems that use V= n/M
Calculate the volume of a 3.50 molar solution of H2SO4 made from 3mol of H2SO4.
Problems that use n=VXM
How many moles of NaOH are in 55.0 liters of a 3.00 M solution?
Volume of solution =55 L
Molarity = mol/L= 3.00 M
Formula n= VM
Number of moles n= = 3.00 mol /L X 55 L= 165 mol