Aim: How can we tell the difference between oxidizing and reducing

agents? Do Now:

1.Take out a calculator and reference tables. 2.Write the oxidation states for each element in

the following compounds: •HClO•NaHCO3

•AgNO3

•Cl2

Answer to do now

HClO

NaHCO3

AgNO3

Cl2

How can we tell if a reaction is a redox reaction?

• Not all reactions are redox reactions. • To determine whether a redox reaction has

occurred, assign oxidation numbers to each atom on the reactant and product sides.

• If there is a change in oxidation numbers for any of the atoms, then a redox reaction has occurred.

• Hint: If an uncombined element becomes part of a compound, it is a redox reaction.

• Hint: Double replacement reactions are not redox.

Practice ProblemsDetermine whether the following are redox reactions:

Zn + HCl ZnCl2 + H2

NaCl + AgNO3 AgCl + NaNO3

MnO2 + 4HCl MnCl2 + Cl2 + 2H2O

Another Problem • In the following reaction, which element is oxidized and

which is reduced? 2Fe3+ + Sn2+ 2Fe2+ + Sn4+

• The Fe gains electrons and is thus reduced. • Because the Fe took its electrons from the Sn, it

oxidized the Sn.• Because the Sn gave its electrons to the Fe, it reduced

the Fe.• The element that is oxidized is said to be a reducing agent.

• The element that is reduced is said to be an oxidizing agent.

Practice ProblemsIn the following reactions, which are the oxidizing

agents and which are the reducing agents? Explain.Co(s) +PbCl2(aq) CoCl2(aq) + Pb(s)

2Fe3+ + Sn2+ 2Fe2+ + Sn4+