Exam 3 Pt. 3 - Electrochemistry (Oxidation-Redox Rxns)

What are oxidation reduction (redox) reactions? What type of reactions are these?

• Reactions with transfer of electrons

combination and single displacement 

What is the purpose of oxidation numbers and state?

• To keep track of electrons during transfer

What is the oxidation number of a single element in its most stable form?

• = 0

What is the oxidation number of single ion?

• = charge of ion

What is the oxidation number of multiple elements in a neutral compound?

• = 0 (sum of charges)

What is the oxidation number/state of polyatomic ions?

• = known charge (sum of charges)

Which ions have fixed oxidation numbers for the most part? What are these charges?

• H = +1

• O = -2

• F = -1

What is the exception to H’s fixed charge? What is it then?

• Except when paired with metal (group 1); charge = -1

When given a compound with multiple atoms, what must you do when asked for its oxidation state/number?

• State oxidation state for EACH atom

What two ways or versions could you be asked when balancing redox equations?

1. Acidic

2. Basic

What is oxidized?

• Losing electrons (more positive)

What is reduced?

• Gaining electrons (less positive)

What are half reactions?

• Splitting up a chemical equation based on oxidization and reduction

In an oxidized half reaction, on which side are the electrons?

• On the right (split up)

In an reduced half reactions, on which side are the electrons?

• On the left (combine)

What is the first step to balancing redox reactions?

1. Assign oxidation state and numbers to ALL ATOMS

What is the 2nd step to balancing redox reactions?

2. Write oxidation and reduction half reactions (no electrons)

What is the 3rd step to balancing redox reactions?

3. Balance atoms that are NOT O or H

What is the 4th step to balancing redox reactions?

4. Balance O by H2O

What is the 5th step to balancing redox reactions?

5. Balance H by adding H+

What is the 5.5 step of balancing redox reactions? What must you look at?

5. 5 Add electrons (look at subscripts and coefficients)

What is the 6th step to balancing redox reactions?

6. If necessary, multiply half reactions by constant, so that electrons are equal

What is the 7th step to balancing redox reactions?

7. Add half reactions together and simplify

If asked for the basic version, what is the 8th step to balancing redox reactions?

8. Add equal number of OH- to both sides to neutralize the H+ to produce H2O

then simplify again (H2O on both sides)

What is a cell in chemistry?

• A battery

What is a galvanic cell?

• A battery that uses redox reactions (transfer of electrons)

What is an anode? On what side is it?

• Electrode where oxidation occurs

on left side

What is a cathode?

• Electrode where reduction occurs

on right side

What is happening to electrons in the anode?

• Losing electrons; getting smaller

What is happening to the ion in the anode?

• Losing electrons; becoming more concentrated 

What is happening to the electrons in the cathode?

• Gaining electrons; getting larger

What is happening to the ions in the cathode?

• Ions combining with electrons; less concentrated

What is the function of a salt bridge in the galvanic cell?

• Connects cathode and anode to maintain charge balance

When is a galvanic cell considered dead?

• Once salt runs out; reaction has reached equlibrium

What is cell notation?

• anode | anode solution || cathode solution | cathode

In cell notation, how are the anode and cathode written?

• __ (s) (e.g. Cu(s))

NO CHARGE

In cell notation, how are is the anode solution and cathode solution written? Example?

• 1 M Cu2+ (aq)