Redox Student Notes.doc

Chemistry 30 Electrochemistry Notes

I Introduction to Electrochemistry

1 Definition

2. Reactions involving a transfer of electrons

i) Reduction:

* The term came from reducing a large amount of ore (containing iron ions) to a small amount of metal.

ii) Oxidation:

*The term came from the explosiveness of reactions involving oxygen.

*Booklet page 5

Chemistry 30 Diner Notes

3. Redox Reactions

Cu2+(aq) + Ni(s) ----> Cu(s) + Ni2+(aq)

Write the two half reactions;

Reduction

Oxidation

** Booklet page 6

4. Oxidizing and Reducing Agents

**Booklet page 7


II Predicting Redox Reactions

1. Steps for Predictions

i)

ii)

iii)

iv)

v)

vi)

2. Examples

a) Predict the most likely redox rxn when chromium is placed into aqueous zinc sulfate

Step i)

ii)

iii)

iv)

v)

vi)


b) Predict the most likely redox rxn when potassium permanganate is slowly poured into acidic iron(II)sulfate solution.

i)

ii)

iii)

iv)

v)

vi)

**Booklet page 10,11

III Creating Redox Tables (With Lab Data)

1. Data;

a)

b)

**Booklet page 12-15IV Balancing Redox Reactions


**When most reactants and products are known but the complete reaction is not on the data table use these rules for balancing in an acidic or basic environment.

1. Rules for an acidic solution

i)

ii)a)

b)

c)

d)

iii)

iv)

v)

2. Acidic example

i) Balance the following redox reaction

CrO42- + SO32- ----> CrO2- + SO42-

Step 1: Split into half reactions ( do one at a time)

Step 2a: Balance all non O or H

Step 2b: Balance O with H2O


Step 2c: Balance H with H+

Step 2d: Balance charge with e-

Other half reaction:

Step 3: Multiply top rxn by 2 and bottom by 3 to balance electrons

Step 4: Combine both reactions

Step 5: Reduce

3. Basic Rules

i) Balance like it was in acidic conditionsii) Switch H+ --> H2Oiii) Switch H2O --> OH-

i) Balance the following redox reaction - basic

Zn + NO3- ----> Zn2+ + N2O

V Oxidation Numbers (States)

1. Definition


2. Rules

i)

ii)

iii)

iv)

v)

3. Examples

What is the oxidation number for each of the following atoms

i) N in N2O N 2 O

ii) N in NO3- N O 31-

iii) C in C2H5OH C 2 H 5 O H

iv) C in C6H12O6 C 6 H 12 O 6

v) C in CO2 C O2


The combustion of glucose in the body to carbon dioxide is:

4. Disproportionation

Sometimes the same substance is both oxidized and reduced. An example of this is the preparation of “elephant toothpaste”.

Use oxidation numbers to determine if this is a disproportionation.

Ex: 3Cl2 + 6OH- à 5Cl- + ClO3- + 3 H2O

VI Balancing Redox Reactions with Oxidation Numbers

1. Steps:

i)


ii)

iii)

iv)

v)

2. Examples

a)

b)

VII Redox Stoichiometry

1. Titration Definition

2. Example


Standardize ( find the [ ] ) the kMnO4 by titrating 10.00 mL of 0.500 mol/L tin (II) chloride with acidified KMnO4.

Evidence:

Trial 1 2 3 4

Final buret (mL) 18.40 35.30 17.30 34.10

Initial buret (mL) 1.00 18.40 0.60 17.30

Volume KMnO4 17.40 16.90 16.70 16.80

Endpoint colordark pint light pink light pink light pink

Endpoint average; 16.80 mL ( they must all be within 0.20 mL)

Analysis:

Determine net ionic redox equation;

Do the Stoichiometry:


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Redox Student Notes.doc