balancing-oxidation-handout

balancing-oxidation-handout - Review: balancing chemical...

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Balancing equations using oxidation numbers C 3 H 8 O + CrO 3 + H 2 SO 4 Cr 2 (SO 4 ) 3 + C 3 H 6 O + H 2 O Review: balancing chemical equations • Balance the following chemical reaction: CuCl 2 + Al Cu + AlCl 3 • In the past (e.g. in grade 11) we balanced equations by “inspection”. • Balancing equations relied on having equal numbers of atoms on each side of the equation • We can balance equations using oxidation #s. • This relies on the idea that the number of electrons lost by an element must be equal to the number gained by a different element. • In other words the total gain in oxidation numbers must be equal to the total lost. Using Oxidation Numbers total oxidation # CuCl 2 + Al Cu + AlCl 3 • Notice: Cu has gained 2e (oxidation # by 2) • Notice: Al has lost 3e (oxidation # by 3) • But, number of e gained must equal e lost • Multiply Cu by 3, Al by 2: change is 6 for both change total oxidation # 3CuCl 2 + 2Al 3Cu + 2AlCl 3 -1 -2 +2 +2 0 0 0 0 +3 +3 -3 -1 -1 -2 +2 +2 0 0 0 0 +3 +3 -3 -1 +6 0 0 +6 +6 -6 Steps to balancing equations 1. Write the skeleton equation 2. Assign oxidation numbers to all atoms
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