Mole

Key Stage 4

Meaning

A mole is an SI Unit used to show 6.02x10²³ particles of a chemical.

About Moles

Moles are based on the number of Carbon atoms in exactly 0.012kg (12g) of Carbon.

Moles are used to give a conversion between the number of atoms in a substance and useful quantities for chemical reactions. It would not be useful to talk about 1,000,000,000 atoms in a chemical reaction because that would be such a small amount of the chemical (0.0000000000000017g).

The relative atomic mass of an element is the mass of 1 mole or the mass of 6.02x10²³ atoms. So 1g of Hydrogen is 1 mole and contains 6.02x10²³ atoms. 235g of Uranium-235 is 1 mole and contains 6.02x10²³ atoms.

Equation

Number of Moles of an Element = (Mass of Element)/(Relative Atomic Mass of Element)

Number of Moles = \({\frac{m}{A_r}}\)

Where:

m = The mass of element being used.

A_r = The Relative Atomic Mass of the Element

Number of Moles of a Compound = (Mass of compound)/(Relative Formula Mass of compound)

Number of Moles = \({\frac{m}{M_r}}\)

Where:

m = The mass of compound being used.

M_r = The Relative Formula Mass of the compound

Calculating Moles

Calculating Moles from Masses

The Periodic Table is needed to for mole calculations in order to find the Relative Atomic Masses of the elements.

Calculating Moles for Elements
Calculate the number of moles in 36g of Carbon	Calculate the number of moles in 2g of Oxygen	Calculate the number of moles in 47g of Uranium-235
Relative Atomic Mass of Carbon = 12g No. Moles = \({\frac{m}{A_r}}\) No. Moles = \({\frac{36}{12}}\) No. Moles = 3mol	Relative Atomic Mass of Oxygen = 16g No. Moles = \({\frac{m}{A_r}}\) No. Moles = \({\frac{2}{16}}\) No. Moles = 0.125mol	Relative Atomic Mass of Uranium-235 = 235g No. Moles = \({\frac{m}{A_r}}\) No. Moles = \({\frac{47}{235}}\) No. Moles = 0.2mol

Calculating Moles for Compounds
Calculate the number of moles in 32g of Methane	Calculate the number of moles in 22g of Carbon Dioxide	Calculate the number of moles in 115g of Ethanol
Chemical Formula of Methane = CH₄ Relative Atomic Mass of Carbon = 12g Relative Atomic Mass of Hydrogen = 1g Relative Formula Mass of CH₄ = 12 + 1 x 4 Relative Formula Mass of CH₄ = 16 No. Moles = \({\frac{m}{M_r}}\) No. Moles = \({\frac{32}{16}}\) No. Moles = 2mol	Chemical Formula of Carbon Dioxide = CO₂ Relative Atomic Mass of Carbon = 12g Relative Atomic Mass of Oxygen = 16g Relative Formula Mass of CH₄ = 12 + 16 x 2 Relative Formula Mass of CH₄ = 44g No. Moles = \({\frac{m}{M_r}}\) No. Moles = \({\frac{22}{44}}\) No. Moles = 0.5mol	Chemical Formula of Ethanol = C₂H₅OH Relative Atomic Mass of Carbon = 12g Relative Atomic Mass of Hydrogen = 1g Relative Atomic Mass of Oxygen = 16g Relative Formula Mass of CH₄ = 12x2 + 1x6 + 16 Relative Formula Mass of CH₄ = 46g No. Moles = \({\frac{m}{M_r}}\) No. Moles = \({\frac{115}{46}}\) No. Moles = 2.5mol