Molarity:  Molarity is the concentration of a solution expressed as the number of moles of solute per litre of solution.

#### Explanation:

To get the molarity, you divide the moles of solute by the litres of solution.

For example, a 0.25 mol/L NaOH solution contains 0.25 mol of sodium hydroxide in every litre of solution.

To calculate the molarity of a solution, you need to know the number of moles of solute and the total volume of the solution.

To calculate molarity:

1. Calculate the number of moles of solute present.
2. Calculate the number of litres of solution present.
3. Divide the number of moles of solute by the number of litres of solution.

EXAMPLE:

What is the molarity of a solution prepared by dissolving 15.0 g of NaOH in enough water to make a total of 225 mL of solution?

Solution:

Some students prefer to use a “molarity triangle”.

## Units:

In the International System of Units (SI) the coherent unit for molar concentration is mol/m3. However, this is inconvenient for most laboratory purposes and most chemical literature traditionally uses mol/dm3, which is the same as mol/L. This traditional unit is often denoted by the letter M, optionally preceded by an SI prefix as needed to denote sub-multiples, for example:

mol/m3 = 10−3mol/dm3 = 10−3mol/L = 10−3 M = 1 mmol/L = 1 mM.

The units millimolar and micromolar refer to mM and μM (10−3 mol/L and 10−6 mol/L), respectively.

error: Content is protected !!