General Chemistry II Workshop 10: Redox Reactions and Electrochemistry (10 point

Question

General Chemistry II Workshop 10: Redox Reactions and Electrochemistry (10 points total) In the next workshop we will be looking at Electrochemistry. some basic redox chemistry. redox reaction. Before we can do this we must review A chemical reaction that involves the transfer of electrons is called a Here is an example: Zn (s) + Cu2+ (aq) ? Zn2+(aq) + Cu (s) Cu. ion. In this In this reaction two electrons are transferred from the solid Zn to the aqueous C process the solid Zn became a Zn2 ion. This means that the solid Zn lost 2 electrons over of the reaction and went from an oxidation state of Zn(0) to an oxidation state o lon became solid Cu. This means that the Cuž* ion gained 2 electron and went from an oxidation state of Cu(+2) to an oxidation state of Cu(O). f Zn(+2). The Cu2+ s over the course of the reaction which By looking at the change in oxidation state of the species in question you can determine species gained electrons ( this species is being reduced and is called the oxidizing agent) and which (this species is being oxidized and is called the reducing agent). The following of oxidation state rules that you must learn. These rules will help you determine the provides a list oxidation states of all other atoms: 1. The oxidation state of an atom in an uncombined element 0 2. The oxidation state of a monatomic ion the charge of the ion 3. Oxygen usually has an oxidation state of -2 in covalent compounds (except in peroxides, where it is-1) 4. Hydrogen always has an oxidation state of +1 in covalent compounds and-1 when combined with metals 5. Fluorine always has an oxidation state of-1 in covalent compounds 6. The sum of all oxidation states in a neutral covalent compound 0 7· The sum of all oxidation states in a charged covalent compound-the charge on the ion Let's explore Redox Chemistry 1. What is the oxidation number of sulfur in the following chemical species? a. S 042 b.H2S 2. Balance the following reactions. For each reaction, indicate if it is a redox reaction. For each redox reaction, name species that is being oxidized and reduced, name the reducing agent and the oxidizing agent, and show how the oxidation states change. b. HNOs(aq)+AI(s)A(NO3)s(aq) H2(g) YES/NO

Explanation / Answer

1.

a) S2O42-:

Suppose the oxidation number of S is x.

2(x) + 4(-2) = -2

2x - 8 = -2

2x = -2 + 8

x = +6/2 = +3

So, the oxidation number of S in S2O42- is +3.

b) H2S:

Suppose the oxidation number of S is x.

2(+1) + x = 0

2 + x = 0

x = -2

So, the oxidation number of S in H2S in -2.

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