The Mole – Amount of a Substance
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MolesThe MoleThe ‘amount of a substance’ is often measured in grams. It could also be measured by counting the number of atoms, ions, or molecules present. However, because atoms weigh so little, it is more convenient to work on a larger scale and use moles.I mole- One mole of particles contains the same number of particles as there are atoms on exactly 12 of carbon 12.Avogadro’s number600,000,000,000,000,000,000,000This number is approximately 6 x 1023. The mass of 1 mole of a substance is equal to its Relative Mass in grams.Basic Mole EquationsE.g. Find the mass of:1 mole of chlorine atoms 35.5 g1 mole of water 18 g1 mole of sodium chloride 23 + 35.5 = 58.5 gE.g. What is the mass of 0.75 moles of carbon?1 mole C = 12 g0.75 moles C = 12 x 0.75 g = 9 gE.g. How many moles of carbon are there in 10 g?12 g contains 1 mole (as Ar C = 12)12 g = 1 mole1 g = moles[pic 1]10 g = 10 x moles[pic 2] = 0.83 molesE.g. How many moles of hydrogen atoms are there in 1 mole of ethanol (C2H6O)?The formula of ethanol, C2H6O, tells us that 1 mole of ethanol contains:2 moles of carbon atoms 6 moles of hydrogen atoms1 mole of oxygen atomsE.g. Find the mass of chlorine in 10 g of magnesium chloride:1st find how many moles of MgCl2 there are:Atomic mass95 g = 1 mole MgCl21 g = moles[pic 3]
10 g = 10 x moles[pic 4] = 0.1053 moles of MgCl2MgCl2 : Cl1 : 20.1053 : 0.2105 moles of Cl atoms1 mole of Cl = 35.5 g0.2105 moles = 35.5 x 0.2105 g = 7.47 g of Cl in 10 g of MgCl2StoichiometryStoichiometry or balancing of an equation can be found if the masses of the reactants and products in a particular reaction are known.E.g. Work out the stoichiometry for the reaction between 1.6 g of methane and 4.8 g of oxygen forming 3.6 g of water and one other productCH4O2H2OMass1.64.83.6Mr163218Moles0.10.150.2÷ Smallest11.52Ratio2342CH4 + 3O2 2CO +4H2O[pic 5]Further Moles and EquationsHow to work out complicated equationsWrite a balanced equationConvert mass into molesUse the equationConvert moles into massE.g. What mass of water vapour is formed when1.6 g of methane burns?Step 1EquationCH4 + 2O2 CO2 + 2H2O [pic 6] 1.6 g ?gStep 2Mass Moles[pic 7]16 g = 1 mole1 g = moles[pic 8]