Mole Concept and Molar Mass in Chemistry

Mole

The mole, denoted as (mol), is the SI unit representing the amount of substance.

One mole

One mole is the amount of substance which contains the same number of particles as 12.0 g of Carbon-12.

Avogadro's number

Avogadro's number, also known as the Avogadro constant is the number of particles in one mole of any substance.

Avogadro's Number (NA)

NA = 6.022 x 1023

Molar Mass

The mass of one mole of substance is called the molar mass (or molecular weight). The unit of molar mass is g/mol.

Mole Ratio

A mole ratio is a conversion factor that relates the number of moles of different substances in a balanced chemical equation.

Conversion between mole and Avogadro's number

3 moles of HCl contain ................... HCl molecules.

Moles in atoms of Zinc

How many moles are in 3.01 x 1023 atoms of Zinc?

Molecules in water

How many molecules do 2.5 moles of water contain?

Moles of chlorine gas

How many moles of chlorine gas are there in 8.33 x 1023 molecules?

Molecules in carbon dioxide

How many molecules are in 0.25 mol of carbon dioxide?

Calculating Molar Mass

To find the molar mass of a compound, you need to sum the atomic masses of all the atoms in the compound, taking into account the number of each atom present.

Example of Molar Mass Calculation

Calculate molar mass of the following compounds: H₂O, Sodium Carbonate, Potassium Sulfate.

Stoichiometric relationship

It is a way to express the stoichiometric relationship between reactants and products in a reaction.

Coefficients in Mole Ratio

To determine the mole ratio, compare the coefficients of each of the substances in the equation.

Mole Ratio Example

The mole ratio of the above equation is 2 : 1 : 2.

Mole Ratio of Hydrogen to Water

What is the mole ratio of hydrogen gas to water in the following equation: H2 (g) + O2 (g) H2O (l)?

Avogadro's constant

The number of particles in one mole of a substance, approximately 6.022 x 10²³.

Chemical amount in moles

Calculated using the formula n = m / MM, where n is the amount in moles, m is mass in grams, and MM is molar mass in g/mol.

Percentage composition

The mass percentage of each element within a compound, calculated by dividing the mass of an element by the total mass of the compound and multiplying by 100.

Molecular formula

A formula that shows the actual number of each type of atom in a molecule.

Empirical formula

A formula that shows the simplest whole-number ratio of atoms in a compound.

Calculation of moles

The amount of substance n, in moles, can be calculated for a given mass of substance using the formula n = m / M.

Example of moles calculation

For 64g of oxygen (O2), n = 64 g / 32.0 g/mol = 2.0 mol O2.

Percentage composition of sodium carbonate

To determine, divide the mass of sodium by the total mass of sodium carbonate and multiply by 100.

Percentage composition of Hydrogen in water

Calculated by dividing the mass of Hydrogen in water by the total mass of water and multiplying by 100.

Example of empirical formula calculation

For a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen, the empirical formula is CH2O.

Steps to calculate empirical formula

1. Convert mass percentages to grams. 2. Convert mass to moles. 3. Divide by the smallest number of moles. 4. Write the empirical formula.

Example of empirical formula from mass

A compound with 20.32 g of Carbon, 5.12 g of Hydrogen, and 7.9 g of Nitrogen needs to be analyzed to find its empirical formula.

Mass of sodium chloride

To find the mass of 0.2 mol of sodium chloride, multiply the number of moles by the molar mass of sodium chloride.

Finding moles of potassium bromide

Calculate the number of moles in 2.48 g of potassium bromide using the formula n = m / M.

Finding moles of carbonate

Calculate the number of moles in 6 kg of carbonate using the formula n = m / M.

Finding moles of hydrogen

Calculate the number of moles in 10 g of hydrogen using the formula n = m / M.

Diatomic molecule

A molecule composed of two atoms, such as O2.

Mass of glucose sample

To find the number of moles in a 1.52 kg sample of glucose C₆H₁₂O₆, convert kg to g and use the formula n = m / M.