[Chemistry Class Notes] Molarity Pdf for Exam

In this section, the simplest definition and Molarity formula will be explained with proper examples. You will find out how this formula is derived and how it can be used in different ways. After studying this section, you will find it convenient to understand the Molarity definition and formula properly. It is an important term used in different chapters. Hence, learning this formula will become absolutely mandatory.

 

Students have been taught various units of measurement, be it in Mathematics, Physics, or Chemistry as well. When it comes to Chemistry, there are various units of measuring different substances – their volume, concentration, etc.,- and one such unit which is widely used in Chemistry is the ‘mole’. 

 

Now, what is a mole? A mole is a unit of measurement used for a chemical substance from which comes the term ‘Molarity’. Molarity, also known as the molar concentration of a solution is the technique of calculating the amount of substance a particular chemical solution contains. It is measured by considering two indicators, that is, the number of moles that are present in the solute and the volume of the solution. The volume of the solution is essentially calculated in the unit of liters. Molarity is symbolized by ‘M’.

Definition of Molarity (M)

Molar Concentration or Molarity is defined as the number of moles of solute present in a definite amount of liters of the solution, that is, moles per liters of a solution.

 

Difference between Solute, Solvent, and Solution

Before going ahead, let us know the difference between the terms ‘solute’, ‘solvent, and ‘solution’ to make it easier to understand the concepts that are going to come ahead. A solution can be defined as a homogeneous mixture that contains one or more solutes in it, which means that solutes are nothing but materials that are present in solutions. A solvent is a substance that can dissolve a solute. Therefore, what we call a solution is nothing but a solute that is dissolved into a solvent, forming a solution.

 

Molality (m) – A Brief Introduction

The term Molality was first found in a publication that goes by the name “Thermodynamics and the Free Energies of Chemical Substances”, which was published in the year 1923 by G N Lewis and M Randall. It is symbolized by ‘m’.

 

Definition of Molality (m)

Molality can be defined as the number of moles of a solute that can be found in a kilogram of the solvent, that is, moles per kilogram of a solvent.

 

Difference between Molarity and Molality

Though the terms Molarity and Molality may seem somewhat similar as the two words sound almost the same, the sharp contrast between them and their usage makes it very important for the students to understand and to know, as it creates a huge difference while using it for various calculations. It may be difficult to notice and sometimes escape the eyes of the students, but there is one important distinction between the two terms Molarity and Molality. 

Molarity is the calculation of the number of solutes that are present in a liter of a solution. As we have mentioned earlier, a solution contains both the solute and the solvent. Whereas, Molality is the calculation of the number of solutes that are present in a kilogram of the solvent itself. As we already know, a solvent is something that dissolves the solute.

 

Mole Fraction – Definition 

As we know, a solution is a mixture of various constituents, and the Mole Fraction, which can also be called the Molar Fraction, is defined as the amount of one particular constituent, which is expressed in terms of moles divided by the total amount of all the constituents present in the solution.

 

Weight Percentage – Definition

The Weight Percentage, which can also be termed as the Mass Percentage is nothing but the ratio of the mass of a solute and the mass of a solution, multiplied by 100. 

Easy Way to Define Molarity with Formula

There are different terms used in the advanced syllabus of Chemistry. NCERT Chemistry has a set of physical chemistry where you will find a lot of new terms included and explained in every chapter. These terms are sometimes interlinked and have close meanings too. One such common term introduced in the advanced level chemistry by NCERT is molarity. Along with this term, you will also learn what morality and normality are.

Molarity is a new term for students who have just entered the advanced segment of chemistry. Different types of units will be introduced in Physical Chemistry. These units are used to measure the concentration of solutions and different constituents of a mixture. 

Molarity is defined as the concentration of solute in a solvent. You can refer to it as the easiest way to represent the concentration of a solute in a solution. To understand the actual definition of this term, you will have to understand what molecular weight is. The first step is to understand that the total weight of a molecule of a solute is called its molecular weight. 

 

The atomic weight of every constituent atom of the molecule is added to get the total weight of the solute’s molecule. When this molecular weight is expressed in grams, it represents one mole of that particular substance. This is what you have learned in your previous classes.

 

Let us recapitulate once more. One mole of a substance is the molecular weight of that substance expressed in grams. After learning what mole is, we can proceed to find out what the formula for Molarity is and how it is determined.

 

How Is the Correct Formula of Molarity Determined?

The correct formula of Molarity can only be determined when you know the proper definition of the term and the meaning of all the other chemical terms used to build the formula. As per the definition, the molarity of a solution is the total number of moles of solute present in a particular volume of solution.

 

If we represent everything with symbols then,

 

M = n/V

 

Here, ‘M’ stands for molarity, ‘n’ represents the number of moles of solute present in the solution and ‘V’ represents the volume of solution present in a container. 

 

Now that you have studied what mole stands for, you can easily calculate the amount of solute present in a particular solution. After learning the Molarity definition and formula, you should try some examples that show how molarity can vary and how it can be determined. These examples will also help you to find out other terms associated with the formula. In a nutshell, every problem related to molarity can be solved once you get familiar with the term and its formula.

 

Examples Used to Explain Molarity

The next section of this description page will take you to the explanation of examples. In this section, you will learn how the formula mentioned above can be used to calculate other associated terms. The explanation of the Molarity formula with examples will help you grab the concept better as the experts have used simple language.

 

Let us consider an example to keep this interesting discussion running. If one mole of calcium carbonate (CaCO3) is 100g. It means that the molecular weight of calcium carbonate is 100. Moving on, if this amount of calcium carbonate is present in 4 liters of a solution, then molarity will be:

M = n/V

 

= ¼

 

= 0.25 mol/liters

 

You can understand how this calculation using the formula of Molarity has been done. Do not forget to put on the unit of molarity after the calculation is done.

 

If you consider another example to understand the Molarity ka formula, you will learn a new trick. There are different kinds of solutions you will study in advanced-level chemistry. When the solute and solvent are both liquids, do not forget to consider the resultant volume of the solution. For instance, when 1 liter of sulphuric acid is mixed in 2 liters of water, the solution will become 3 liters. If you know what is the formula of Molarity, then you will understand that the volume of both liquids will be considered.

 

The use of the Molarity formula in Chemistry is exemplary. You will find it in different chapters of inorganic chemistry too. Hence, you should learn the definition and Molarity formula properly using the explanation given by the experts.

Conclusion

This is all about the concept of molarity and its difference from molality. Make sure you understand both terms well so that you can identify the right formula to derive the solutions to problems easily.  Focus on the examples given here to understand molarity better.