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Molarity

A chemistry teacher who teaches General Chemistry at the K-12 level..

Molarity

Molarity, an expression of concentration is expressed as a ratio of moles of solute to volume of solution in Litres or dm^3.

preparation of a molar solution

preparation of a molar solution

Molarity Calculations

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

  1. The information given to you in the problem along with the appropriate units
  2. You must then write the formula that you will use to solve the numerical
  3. At times you will have to modify the formula suited to the needs of the problem
  4. Then, substitute the given values in your formula
  5. 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?

Given:

Moles of NaCl= 0.5 mol

Volume of solution= 0.3L

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Formula: M=n/V

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?

Given:

Volume of solution =55 L

Molarity = mol/L= 3.00 M

Moles =?

Formula n= VM

Substitute

Number of moles n= = 3.00 mol /L X 55 L= 165 mol

Calculate -

molesVolumeMolarity

0.5

?

0.01M

?

3L

0.25 M

0.1

5L

?

Lab preparation of a solution

Preparation of a solution in the lab

Preparation of a solution in the lab

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