Redox reactions

Redox reactions for edexcel AS Chemistry

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Rules for oxidation numbers

1)The oxidation number of any uncombined element is always 0.

2)The oxidation number of any uncombined ion is always the same as its charge.

3)The sum of all oxidation numbers in a molecule is 0.

4)Flourine always has an oxidation number of -1.

5)Hydrogen always has an oxidation number of +1, expect in metal hydrides when it is -1.

6)Oxygen has an oxidation number of -2, except in peroxides when it is -1.

7)Chorine always has an oxidation number of -1 except with oxygen and flourine when positive.

8)Group 1 elements always have +1, group 2 always +2, group 3 always +3 and group 7 always -1.

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Balancing equations using oxidation numbers

Step 1) write down all of the oxidation numbers in a reaction that change.

Step 2) calculate the total change for each element (product ON - reactant ON)

Step 3) calculate the electron transfers for each element.

Step 4) Balance the electron transfers, (multiply the element to increase ON)

Step 5) Balance oxygens by adding water to the right side.

Step 6) Balance the hydrogens by adding H+ ions to the left hand side.

Step 7)Add up all the charges and check they balance.

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