Moles

In chemistry a mole is a quantity of atoms, just like a ream of paper is a quantity of sheets of paper A ream of paper is 500 sheets of Paper. What is a chemical mole? A mole of atoms is 6.02 x atoms That’s atoms

Why do we need moles? Atoms and molecules are very small so they cannot be counted directly. In chemistry we usually weigh out elements and compounds. However, simply weighing something does not tell us how much there is (i.e. how many atoms or molecules). For example lead atoms are much bigger than hydrogen atoms, so 5g of hydrogen would contain far more atoms than 5g of lead.

6.02 X Blood Cells: Would be more than the total number of blood cells found in every human on earth x = a big number! 6.02 X Watermelon Seeds: Would be found inside a melon slightly larger than the moon X Pennies: Would make at least 7 stacks that would reach the moon.

A special number Also known as Avagadro’s number (constant) Amedeo Avogadro Is the number of atoms in 1 mole of a substance. But also: It is the number of atoms in exactly 12g of carbon

Moles are related to Relative Atomic mass Carbon has a relative atomic mass of12 As we weigh things in grams we say that in 12g of carbon atoms there is 1 mole of carbon atoms The relative atomic mass of hydrogen is1 Therefore a hydrogen atom is 12 times lighter than a carbon atom. Carbon Relative atomic mass = 12 1 mole of carbon atoms weighs 12g 1 Hydrogen Relative atomic mass = 1 1 mole of hydrogen atoms weighs 1g

Hydrogen relative atomic mass =1 1 mole = 1gwhich contains 6 x atoms Carbon, relative atomic mass = 12 1 mole = 12gwhich contains 6 x atoms Oxygen, relative atomic mass = 1 mole = which contains atoms Potassium, relative atomic mass = 1 mole = which contains atoms Arsenic, relative atomic mass = 1 mole = which contains atoms 16 16g 6 x g 6 x g 6 x 10 23

What is the mass of: 1 mole of nitrogen atoms? 2 moles of oxygen atoms? 0.5 moles of copper atoms? How many moles are there in: 11g of Boron atoms? 3g of carbon atoms? 80g of calcium atoms? 14g 32g 1 mole 0.25 moles 2 moles

Useful equation! Number of moles = Mass of element (how much you have) Relative atomic mass of the element For example. How many moles are there in 4 g of calcium? Number of moles = 4 40 = 0.1

MASS MOLES How much you have in g The number of moles you have of the substance FORMULA MASS (Relative atomic mass (atoms) or relative formula mass (molecules and compounds) Magic triangle

Moles are not just for atoms ! You can also have a mole of a molecule or a compound. Diatomic molecules An oxygen molecule contains 2 atoms of oxygen The formula mass of an oxygen molecule is 1 mole of oxygen molecules weighs 1 mole of oxygen molecules contains oxygen molecules OO g 6.02 x 10 23

How many moles in: 28 g of nitrogen molecules? 80g of bromine molecules? 5g of hydrogen molecules? What is the weight of: 1 mole of chlorine molecules? ½ mole of oxygen molecules? 2 moles of ammonia (NH 3 ) molecules? 1 mole 0.5 moles 2.5 moles 70g 16g 34g

Compounds are just like molecules! 1 mol of a compound is the Relative Formula Mass in grams Example: methane (CH 4 ) C 12 H 1 H 1 H 1 H 1 Relative formula mass = Mass of 1 mol of methane = 1 mol of methane contains methane molecules x 10 23