Question

What is molarity? Give its unit.

Answer 1

Hint: The formula for molarity contains two terms, one is mass of solute and other is volume of solution. Molarity is a way to express the concentration of solution.

Complete step by step answer:
Qualitatively, a solution can be described as either dilute solution or concentrated solution. Quantitative descriptions include the concentration of the solution. The concentration of solutions gives information about the amount of solute present in the given amount of solution. Various terms are used to describe the concentration of solute in the solution. These terms include percent by mass, percent by volume, ppm, ppb, normality molarity, molality and mole fractions.

Molarity is the number of moles of solute present per unit volume of the solution. It is obtained by dividing the number of moles of solute with volume of solution. The unit of volume of solution should be in liters.
\[{\rm{Molarity = }}\dfrac{{{\rm{Number of moles of solute}}}}{{{\rm{Volume of solution in liter}}}}{\rm{ }}\]

Thus, if 180 grams (1 mole) of glucose is dissolved in sufficient amounts of water so that total volume of the solution is one liter, then the molarity of the solution is 1 M.
If 1 L of solution contains 18 grams (0.1 moles) of glucose, then the molarity is 0.1 M.
The unit of molarity is mol/L or M.

Note:
Do not mix the concepts of molarity with molality which is expressed as mass of solute divided by mass of solution in kg.