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Moles What is a chemical mole? 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. A mole of atoms is 6.02 x 1023 atoms That’s 602000000000000000000000 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 1023 = a big number! 6.02 X 1023 Watermelon Seeds: Would be found inside a melon slightly larger than the moon. 6.02 X 1023 Pennies: Would make at least 7 stacks that would reach the moon. 6.02 X 1023 Blood Cells: Would be more than the total number of blood cells found in every human on earth. 602000000000000000000000 A special number Also known as Avagadro’s number (constant) Is the number of atoms in 1 mole of a substance. But also: It is the number of atoms in exactly 12g of carbon Amedeo Avogadro Moles are related to Relative Atomic mass Carbon has a relative atomic mass of 12 As we weigh things in grams we say that in 12g of carbon atoms there is 1 mole of carbon atoms Carbon Relative atomic mass = 12 1 mole of carbon atoms weighs1 12g The relative atomic mass of hydrogen is 1 Therefore a hydrogen atom is 12 times lighter than a carbon atom. Hydrogen Relative atomic mass = 1 1 mole of hydrogen atoms weighs 1g Hydrogen relative atomic mass =1 1 mole = 1g which contains 6 x 1023 atoms Carbon, relative atomic mass = 12 1 mole = 12g which contains 6 x 1023 atoms Oxygen, relative atomic mass = 16 1 mole = 16g which contains 6 x 1023 Potassium, relative atomic mass = 1 mole = 39g 39 which contains 6 x 1023 atoms Arsenic, relative atomic mass = 1 mole = 75g atoms 75 23 which contains 6 x 10 atoms What is the mass of: 1 mole of nitrogen atoms? 14g 2 moles of oxygen atoms? 32g 0.5 moles of copper atoms? 32g How many moles are there in: 11g of Boron atoms? 1 mole 3g of carbon atoms? 0.25 moles 80g of calcium atoms? 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 Magic triangle MASS How much you have in g MOLES The number of moles you have of the substance FORMULA MASS (Relative atomic mass (atoms) or relative formula mass (molecules and compounds) 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 16 O 16 O The formula mass of an oxygen molecule is 32 1 mole of oxygen molecules weighs 32g 1 mole of oxygen molecules contains 6.02 x 1023 oxygen molecules How many moles in: 28 g of nitrogen molecules? 80g of bromine molecules? 5g of hydrogen molecules? 1 mole 0.5 moles 2.5 moles What is the weight of: 70g 1 mole of chlorine molecules? 16g ½ mole of oxygen molecules? 2 moles of ammonia (NH3) molecules? 34g Compounds are just like molecules! 1 mol of a compound is the Relative Formula Mass in grams Example: methane (CH4) 1 1 H Relative formula mass = 16 1 H 12 H C 1 H Mass of 1 mol of methane = 16 1 mol of methane contains molecules 6.02 x 1023 methane