# Biochemistry Notes for Class 12 “Molarity” Class 12

**Molarity**

Molarity is based on the volume of solution containing the solute. Since density is a temperature dependent property a solution’s volume, and thus its molar concentration, changes with temperature. By using the solvent’s mass in place of the solution’s volume, the resulting concentration becomes independent of temperature.

Molarity is the common way of referring to concentrations of solutions. The goal of most basic molarity problems shall be to get the moles from grams by dividing the molecular weight and then dividing by the total number of liters or by given the molarity find the number of grams of the solution by multiplying the volume then the molecular weight. Molarity might give you the density of the solution, from which you can obtain the mass by multiplying the density by the volume.

Although there are several ways in which the concentration of a solution can be quantified, molarity is one of the most basic and widely used. Molarity (M) is defined as the number of moles of solute dissolved in one liter of solution. The higher the molarity, the more concentrated or strong the solution is. For example, a 12 M (which is said “twelve molar”) solution of HCl (ie. hydrochloric acid) is much more concentrated than a 0.10 M solution! The basic formula for calculating molarity is:

*Molarity (M) = moles of solute (mol) per liters of solution (L)*

To solve for moles of solvent, we can use algebra to manipulate the above equation producing the following derived formulas:

*moles of solute (mol) = Molarity (M) × liters of solution (L)*

In simple terms, the following formula could be used for preparation of molar solutions for lab solutions preparation

For preparation of molar solution

Molecular weight of the compound (A)/1000

*× Required morality (B) × Required volume of solution (C) = D gram*

In the above equation for preparation of solution of ‘B’ molarity, ‘D’ grams of the solute could be dissolved in ‘C’ ml of solvent.

QUESTIONS

1. ……………….. is based on the volume of solution containing the solute

(a) Normality (b) Molarity (c) Molality (d) Percent

2. Molarity is the common way of referring to ……………….. of solutions