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Difference Between Molecular Mass and Molar Mass for JEE Main 2024

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Last updated date: 22nd Jul 2024
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What is Molecular Mass and Molar Mass: Introduction

To explain molecular mass and molar mass: Molecular mass refers to the mass of a single molecule and is calculated by summing up the atomic masses of all atoms in the molecule. It is expressed in atomic mass units (amu). On the other hand, molar mass refers to the mass of one mole of a substance, which is numerically equivalent to its molecular mass or the sum of the atomic masses of its constituent atoms. Molar mass is expressed in grams per mole (g/mol) and is used to convert between the mass of a substance and the number of moles present. Let’s further know about the characteristics of molecular mass and molar mass.


Category:

JEE Main Difference Between

Content-Type:

Text, Images, Videos and PDF

Exam:

JEE Main

Topic Name:

Difference Between Molecular Mass and Molar Mass

Academic Session:

2024

Medium:

English Medium

Subject:

Chemistry

Available Material:

Chapter-wise Difference Between Topics


Defining Molecular Mass

Molecular mass, also known as molecular weight, is the sum of the atomic masses of all the atoms in a molecule. It is calculated by adding up the atomic masses of each individual atom present in the molecule. Molecular mass is expressed in atomic mass units (amu) and provides information about the mass of a single molecule. It is a fundamental property used in various chemical calculations, including stoichiometry, determining the empirical formula of compounds, and analyzing the composition of substances. The properties of molecular mass are:

  • Calculation: Molecular mass is calculated by summing up the atomic masses of all the atoms present in a molecule. It provides the total mass of the molecule.

  • Units: Molecular mass is expressed in atomic mass units (amu) or Daltons (Da). These units represent a relative scale of mass based on the carbon-12 isotope as a reference.

  • Molecular Identity: The molecular mass is specific to each unique molecule. Different molecules have different molecular masses based on the arrangement and types of atoms in their structure.

  • Ratio and Proportions: Molecular mass allows for the determination of the ratio and proportions of different elements within a molecule. This information is crucial for stoichiometric calculations, including determining empirical and molecular formulas and calculating reaction yields.

  • Physical and Chemical Properties: The molecular mass influences various physical and chemical properties of a substance, including boiling point, melting point, solubility, and reactivity. It is a factor in determining the behaviour and interactions of molecules in chemical reactions.


Defining Molar Mass

Molar mass is the mass of one mole of a substance. It is calculated by summing up the atomic masses of all the atoms in a molecule and is expressed in grams per mole (g/mol). Molar mass provides the mass of a given number of particles, allowing for conversions between mass and moles. It is a fundamental property used in stoichiometry, determining the quantities of substances involved in chemical reactions and converting between mass and volume. The properties of molar mass are:

  • Units: Molar mass is expressed in grams per mole (g/mol) or sometimes in kilogram per mole (kg/mol). These units represent the mass of one mole of a substance.

  • Numerical Relationship: Molar mass provides a numerical relationship between the mass of a substance and the number of moles present. It allows for conversions between mass and moles using the concept of Avogadro's number $(6.022 \times 10^23)$.

  • Stoichiometry: Molar mass is a key factor in stoichiometric calculations, which involve determining the quantities of reactants and products in a chemical reaction. It helps establish the mole ratios necessary for balancing equations and calculating reaction yields.

  • Gas Laws: Molar mass is involved in various gas laws, such as the ideal gas law, which relates the pressure, volume, temperature, and number of moles of a gas. Molar mass helps establish the relationship between gas properties and molecular weights.

  • Solution Concentration: Molar mass is used to calculate the concentration of a solute in a solution, such as molarity (moles of solute per liter of solution) or molality (moles of solute per kilogram of solvent).


Molecular Mass and Molar Mass Differences

S.No

Category 

Molecular mass 

Molar mass 

1.

Definition

The sum of the atomic masses of all atoms in a molecule.

The mass of one mole of a substance.

2.

Calculation

Calculated by summing up the atomic masses of the constituent atoms.

Calculated by summing up the atomic masses of all atoms in a molecule or formula unit.

3.

Units

Expressed in atomic mass units (amu) or Daltons (Da).

Expressed in grams per mole (g/mol).

4.

Purpose

Provides the total mass of a single molecule.

Allows conversion between mass and moles of a substance.

5. 

Relationship

Molecular mass is a property of a specific molecule.

Molar mass is a property of a substance as a whole.

6. 

Stoichiometry

Used in determining the empirical and molecular formulas of compounds.

Essential in stoichiometric calculations and reaction yield calculations.


Molecular mass and molar mass are important concepts in chemistry. This table provides a concise overview of the main differences between molecular mass and molar mass, including their purpose, units, calculation, stoichiometry, etc.


Summary 

Molecular mass and molar mass are two distinct concepts in chemistry. The composition and structure of molecules play a significant role in determining their unique molecular masses and play a crucial role in stoichiometric calculations and determining the quantities of substances involved in chemical reactions. Molar mass enables the calculation of reaction yields by converting between the mass of one substance and the moles of another involved in the reaction.

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FAQs on Difference Between Molecular Mass and Molar Mass for JEE Main 2024

1. Why do different molecules have different molecular masses?

Different molecules have different molecular masses because the molecular mass is determined by the types and arrangement of atoms within the molecule. Each atom has a specific atomic mass, and when multiple atoms combine to form a molecule, their individual atomic masses are summed up to calculate the molecular mass. Since different molecules consist of different combinations of atoms, they will have different molecular masses. Therefore, the composition and structure of molecules play a significant role in determining their unique molecular masses.

2. How is molar mass used in stoichiometry?

Molar mass is a crucial component in stoichiometry, where it is used for various calculations. It allows for the conversion between mass and moles of a substance, facilitating the determination of the number of moles of a given mass or vice versa. Molar mass is also essential in balancing chemical equations, ensuring that the ratio of reactants and products is correct. Furthermore, it is used to calculate the empirical and molecular formulas of compounds by comparing the molar mass with the empirical formula mass.

3. What is the relationship between molecular mass and molar mass?

The relationship between molecular mass and molar mass lies in the fact that the molar mass is numerically equal to the molecular mass when expressed in grams per mole. The molecular mass represents the mass of a single molecule, calculated by summing up the atomic masses of all the atoms in the molecule. On the other hand, molar mass represents the mass of one mole of a substance and is determined by summing up the atomic masses of all the atoms in a molecule or formula unit. Thus, the molar mass can be obtained by multiplying the molecular mass by the molar mass constant, which is Avogadro's number (6.022 x 10^23).

4. How is molecular mass different from molar mass?

Molecular mass refers to the sum of the atomic masses of all the atoms in a single molecule, representing the mass of that specific molecule. It is expressed in atomic mass units (amu) or Daltons (Da). On the other hand, molar mass represents the mass of one mole of a substance and is calculated by summing up the atomic masses of all the atoms in a molecule or formula unit. Molar mass is expressed in grams per mole (g/mol) and allows for the conversion between mass and moles of a substance.

5. What units are used to express molecular mass?

Molecular mass is typically expressed in atomic mass units (amu) or Daltons (Da). Atomic mass units are a unit of measurement used to quantify the mass of atoms and molecules on a relative scale. One atomic mass unit is defined as 1/12th the mass of a carbon-12 atom. The molecular mass of a compound is calculated by summing up the atomic masses of all the atoms present in the molecule. It provides a measure of the total mass of the molecules and is essential for various calculations in chemistry, such as determining the stoichiometry of chemical reactions and the composition of compounds.