Chemistry Unit 5 - Using Moles: Moles, Avogadro Constant, Gases and Volume S3B

What is a mole?

A mole is a measure of the amount of particles of matter. A mole is a unit of measuring chemical substances, its unit is mol.

Moles = mass/molar mass

The mole ratio of a compound is the ratio in which each substance can have their mass, amount of moles and particles solved for.

What is molar mass?

Molar mass is the mass of a substance per mole. It is measured in atomic mass units, where 1 amu is 1/12 of a Carbon-12.

• 1 Proton = 1 amu, 1 Neutron = 1 amu

• The atomic mass is found from the mass of the protons plus the neutrons.

• Relative isotopic mass = mass of atom / mass of carbon-12

• Mass of an ion is the SAME as the mass of its original atom. They only gain or lose electrons, which have minute effects on the mass.

• Relative Molecular Mass (or Mr, molar mass) = All Ar (relative atomic mass) values added up together

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What is the molar gas volume at rtp? (20℃ and 1 atmosphere in pressure)

It is 24 dm³.

What is the Avogadro constant?

It is the number of particles of a substance per mole, 6.02 × 10²³. This means different substances have the same number of particles for every one mole. Although their number of particles per mole might be the same, their total mass will still differ because they have different atomic masses/molar masses. Avogradro’s constant applies to all particles, atoms, ions, molecules, etc.

Na = Symbol for Avogadro constant. The a can also be capital.

Number of particles = number of moles x Avogadro constant

How do we find the percentage purity of a substance?

% purity = mass of pure substance/total mass x 100

How do we find the percentage by mass of a substance?

% by mass = Relative atomic mass of substance/relative atomic mass of compound

OR: % by mass = Ar of substance/Total Ar of compound

State the law of conservation of mass.

The mass of the products in a chemical equation is equal to the mass of the reactants in the same equation because the atoms are not gained nor lost, only rearranged.

Elements always react in the same ratio to form a given compound