mole concept molar mass and percentage composition - Overview, Structure, Properties & Uses

Q: How is a mole similar to a dozen?

One mole of substance consists of 6.022×10 23 atoms and is similar to the amount of atoms in carbon that is 12g for one mole. A dozen is equal to 12. So dozen and mole are similar.

Mole Concept Molar Mass and Percentage Composition with FAQs

Edited By Team Careers360 | Updated on Jun 30, 2022 07:31 PM IST

In this article we will cover the topics molar mass definition, molar mass formula, molar mass units, molecular weight definition, molecular weight formula, mole concept, gram molecular weight. Mole is defined as the amount of substance. It will define the identity of a substance by knowing the number of ions or atoms present in it. For water and hydrogen peroxide, both contain hydrogen and oxygen but their properties are extremely different just by the difference in the number of oxygen present in them. So the knowledge of the quantity of the substance is very important. The number of moles is calculated by using the equation,

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No. of moles= Given mass/molecular mass
Mole Concept
Define Molecular Mass
Molar Mass Equation
Percentage Composition
What is Molecular Mass?
Molecular Mass Formula
Formula Mass

No. of moles= Given mass/molecular mass

The number of entities present in one mole is determined experimentally by Avogadro and its value is 6.022×10²³. This number is called the Avogadro number and is very important in chemistry. It is also represented by the letter N_A. Its unit is per mole. The number of moles of any substance can be calculated by dividing the total number of particles in a molecule by the Avogadro's constant. Hence it indicates that one mole of a substance contains 6.022×10²³/mole. For example, for one mole of a carbon atom, there are 6.022×10²³ atoms of carbon.

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Mole Concept

From the definition of the mole, 1 mole of any element contains the same number of atoms for any other element with one mole From the definition of the mole, 1 mole of any element contains an equivalent number of atoms for the other element with one mole. The mass of 1 mole of each element is different thus the mass of each atom will be different.

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As the mole definitions and atomic mass unit definitions deal with the same substance i.e., 12C, thus the molar mass of each substance is equivalent to the atomic weight in amu. According to the mole definition, 12 g of carbon 12 contains 1 mole of carbon 12 atoms. Based on the definition of the mole. The molecular weight of carbon is 12g/mol. This relation will hold for every element since their atomic masses are measured concerning the 12C in amu.

And the molar mass of a compound in grams is also numerically equal to its formula mass in amu. And also atomic mass and molar mass are equal in their respective magnitudes, but they are vastly different in terms of scale. Let us take an example for a drop of water, the number of molecules in the drop of water is roughly 100 billion times greater than the total number of people on earth. So it represents that for a tiny fraction of 1 mole of water, it contains more water molecules. And there will be 100 billion molecules per individual on earth. Therefore a mole is used to represent 6.022×10²³ atoms but it is such a large number we cannot even imagine.

Gram Molecular Mass of C

For one mole of substance when the mass is expressed in grams it is called gram molecular mass. For carbon gram molecular mass is 12g. For water H₂O The gram molecular weight is 2+16 =18g. Since the value of atomic mass for H and O is 1 and 16 and water molecules contain 2 hydrogen atoms.

What is Molar Mass?

Define Molecular Mass

The molar mass of a substance or molecular mass is defined as the total mass of one mole of a substance. That is 6.022×10²³ the number of particles. Atomic mass is different from molar mass in the aspect that atomic mass refers to the mass of one single atom of an element and the and its unit is atomic mass unit ‘u’. 1 amu is equal to 1.66×10^-24g.

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Molar Mass Equation

Molar mass is the ratio of a given mass to the number of moles.

The molar mass formula or molecular weight formula used to calculate the molar mass of the element or the compound is given as shown below.

Molar mass= mass/ no of moles.

Percentage Composition

Percentage composition tells the percentage of each element in a given compound. The equation that can be used for calculating percentage composition is shown below.

Percentage composition=(Mass of individual component/mass of the mixture)×100

What is Molecular Mass?

Molecular weight definition-

The mass of a single molecule in a compound is defined as its molecular mass. By calculating the molecular mass of a compound, we need to add the atomic mass units of respective atoms in it. The unit of molecular mass is commonly Dalton and is represented by Da. 1Da=1u.

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Molecular Mass Formula

The molecular mass of molecules is calculated by multiplying the molar mass of atoms by the number of atoms in each molecule. Some of the examples for molar mass calculation are shown below.

For Cl₂ The molecular mass is twice the amu of Cl. And 1 amu of Cl is 35.453u.

That is the molecular mass of Cl₂= 2×35.453×1.000g/mol=71g/mole.

SI unit of molar mass

The molar mass unit is kg/mol but is also expressed in grams per mole.

What is molecular weight?

Molecular weight is defined as the mass of a molecule in comparison to molar mass; it is the mass of a mole of a particular substance. Its unit is amu, which is an atomic mass unit. It is obtained by adding the atomic weights of individual atoms in a molecule.

Molecular weight unit

The unit of molecular weight is the same as that of molecular mass that is g/mole.

What is gram molecular mass?

The molecular mass of a substance expressed in grams is called the gram molecular mass and it is numerically equal to its molecular mass.

What is gram molecular weight?

The molecular weight of a substance expressive in grams is the gram molecular weight. It is numerically equal to the value of molecular weight.

Formula Mass

The formula of a chemical substance represents the type and the number of atoms present in a chemical substance. The water molecule contains two hydrogen atoms and one oxygen atom. So, the chemical formula of water is H₂O and one oxygen atom and the molecular mass of water can be calculated from its atomic mass as 18g. Therefore, the molecular mass is calculated from the formula of a particular substance. Hence it is also called formula mass.

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Frequently Asked Questions (FAQs)

1. Which is an organic compound having molecular mass 60?

The organic compound with molecular mass 60 is urea that is (NH₂)₂CO. The empirical weight of this compound is 60g and the given molecular weight is 60g. Molecular formula= (Empirical formula)n from which n can be calculated as,

n=60/60=1

So the compound is urea.

2. What is the unit of molecular mass?

The unit of molecular mass is g/mole.

3. What is molecular weight measured in?

It is the weight of one mole of a given compound.

4. How is a mole similar to a dozen?

One mole of substance consists of 6.022×10²³ atoms and is similar to the amount of atoms in carbon that is 12g for one mole. A dozen is equal to 12. So dozen and mole are similar.

5. What is the mass of a carbon atom in a gram?

Mass of carbon atom is obtained by dividing molecular mass by Avogadro number and is 1.9944×10^-23g.

6. What is the molar mass of CH4?

By adding the atomic mass of carbon atom and four hydrogens atom the molar mass of methane can be easily calculated 12.011+4(1.008) =16.043g.