Chapter 9.1

Question 1

Intrduction to Redox Reactions?

What is an oxidation reaction?

Answer 1

It involves the gain of oxygen or the loss of hydrogen, or loss of electrons

Question 2

Introduction to Redox Reactions

What is a reduction recation?

Answer 2

It involves the gain of hydrogen or the loss of oxygen, or gain of electrons

Question 3

Introduction to redox Reactions

What is special about redox reactions?

Answer 3

Oxidation and reduction
will always occur together

Question 4

Oxidation Numbers Enable Us to Track Redox Change

How can we determine the movement of electrons happening in a covalent bond?

Answer 4

Oxidation states

Question 5

Oxidation Numbers Enable Us to Track Redox Change

What is an oxidation state?

Answer 5

A value we assign to each atom in a compound that is a measure of the electron
control or possession it has relative to the atom in the pure element

Question 6

Oxidation Numbers Enable Us to Track Redox Change

What do the signs and values of the oxidation states determine?

Answer 6

The positive sign shows a loss of electeron control while a negative sign shows a gain of control in electrons. The value shows how many electrons the atom has gained or lost

Question 7

Strategy for Assigning Oxidation States

What is the oxidation state of free elements (uncombined)?

Answer 7

Zero

Question 8

Strategy for Assigning Oxidation States

What is the oxidation state of simple ions?

Answer 8

It is the same as their charge

Question 9

Strategy for Assigning Oxidation States

What is the oxidation states of atoms in neutral compound?

Answer 9

Add up to zero

Question 10

Strategy for Assigning Oxidation States

What is the oxidation states of all atoms ina polyatomic ion?

Answer 10

They must add up to charge on ion

Question 11

Strategy for Assigning Oxidation States

What is the ususal oxidation state for an element?

Answer 11

The charge of its most common ion

Question 12

Strategy for Assigning Oxidation States

What is the oxidation states of most non-metals and transition elements?

Answer 12

Vary in different compounds –
depending on the conditions and other elements present

Question 13

Strategy for Assigning Oxidation States

What are the usual oxidation numbers for Li, Na, K, H

Answer 13

+1

Question 14

Strategy for Assigning Oxidation States

What are the usual oxidation numbers for Mg, Ca

Answer 14

+2

Question 15

Strategy for Assigning Oxidation States

What are the usal oxidation numbers for F, Cl

Answer 15

–1

Question 16

Strategy for Assigning Oxidation States

What is the usual oxidation state of O?

Answer 16

–2

Question 17

Interpreting Oxidation States

What does a higher poistive number in the oxidation state mean?

Answer 17

The more the atom has lost control over electrons, in other words the more
oxidized it is.

Question 18

Interpreting Oxidation States

What does a higher negative number in the oxidation state mean?

Answer 18

The more the atom has gained control over electrons, in other words the more reduced it is

Question 19

Interpreting Oxidation States

What does an increase and decrease in oxidation state mean?

Answer 19

An increase in oxidation stae signifies oxidation and a decrease signifies reduction

Question 20

Systematic names of compounds use oxidation numbers

How is oxidation number shown in the element?

Answer 20

Oxidation number is
shown by inserting
a Roman numeral
in brackets after the
name or symbol of the
element.

Question 21

Redox Equations

What are half-equations?

Answer 21

Equations that represent the seperate oxidation and reduction of elements

Question 22

Redox Equations

What are half-equations?

Answer 22

Equations that represent the seperate oxidation and reduction of elements

Question 23

Redox Equations

What are the steps to follow in order to determine the full redox reaction?

Answer 23

1. Assign oxidation states to determine which atoms are being oxidized and which are being reduced.
2. Write half-equations for oxidation and reduction as follows:
   (a) balance the atoms other than H and O;
   (b) balance each half-equation for O by adding H2O as needed;
   (c) balance each half-equation for H by adding H+ as needed;
   (d) balance each half-equation for charge by adding electrons to the sides with the more positive charge.
   (e) check that each half-equation is balanced for atoms and for charge.
3. Equalize the number of electrons in the two half-equations by multiplying
   each appropriately
4. Add the two half-equations together, cancelling out anything that is the same
   on both sides.

Question 24

**Oxidizing and Reducing Agents **

What is the oxidizing agent?

Answer 24

The reactant that accepts electrons, it brings about oxidation of the other reactant. In the
process it becomes reduced

Question 25

# **Oxidizing and Reducing Agents ** What is the reducing agent?

Answer 25

The reactant that supplies the electrons, it brings about reduction and itself becomes oxidized

Question 26

# **Oxidizing and Reducing Agents** What are examples of oxidizing agents?

Answer 26

O2, O3, H+/MnO4–, H+/Cr2O72–, F2, Cl2, conc. HNO3, H2O2

Question 27

# **Oxidizing and Reducing Agents ** What are examples of reducing agents?

Answer 27

H2, C, CO, SO2, reactive metals

Question 28

# **Oxidizing and Reducing Agents ** Whether a species acts as an oxidizing or as a reducing agent actually depends on what?

Answer 28

What is it reacting with as agents can act as either reducing or oxdizing agents based on what they are reacting with

Question 29

# Oxiadizing and Reducing Agents Why is water used as a solvent in redox reactions?

Answer 29

Water is weak both as an oxidizing agent and as a reducing agent

Question 30

# **More reactive metals are stronger reducing agents** What does the strength of oxidizing and reducing agents depend on?

Answer 30

Their relative tendencies to lose or gain electrons

Question 31

# **More reactive metals are stronger reducing agents** Why do metals work as reducing agents?

Answer 31

Have a tendency to lose electrons and form positive ions

Question 32

# **More reactive metals are stronger reducing agents** What makes a metal a strong reducing agent?

Answer 32

The ability to lose electrons more readily than others, which means being more recative

Question 33

# **More reactive metals are stronger reducing agents** How can we check if the metal is more reactive than another?

Answer 33

If it is able to reduce ions of other metal

Question 34

# **More reactive non-metals are stronger oxidizing agents** Why do non-metlas work as oxidizng agents?

Answer 34

React by gaining electrons and forming negative ions, remove electrons from other substances

Question 35

# **More reactive non-metals are stronger oxidizing agents** What makes a non-metal a strong oxidizing agent?

Answer 35

The ability to gain electrons more readily which decreases down a group

Question 36

# **More reactive non-metals are stronger oxidizing agents**

Question 37

# **More reactive non-metals are stronger oxidizing agents** How can we check if the non-metal is more reactive than another?

Answer 37

A more reactive nonmetal is able to oxidize the ions of a less reactive non-metal.

Question 38

# **Redox Titration** What is a titre?

Answer 38

The volume of the solution added from the burette to reach equivalence

Question 39

# **Redox Titrations** What does the analysis of iron with manganate(VII) involve?

Answer 39

This redox titration uses KMnO4 in an acidic solution as the oxidizing agent, which oxidizes Fe2+ ions to Fe3+, MnO4– is reduced to Mn2+,

Question 40

What does the reaction of iron with manganate(VII) result in?

Answer 40

Colour change from deep purple to colourless

Question 41

# **Redox Reaction** What is the full redox reaction of iron with manganate(VII)?

Answer 41

Page 420

Question 42

# **Redox Reaction** What does the iodine-thiosulfate reaction involve?

Answer 42

The reaction of excess iodide with an oxidizing agnet(KMnO4, KIO3, K2Cr2O7, NaOCl) to form iodine

Question 43

# **Redox Titrations** What happens to the liberated iodine molecules?

Answer 43

They are titrated against sodium thiosulfate using starch as indicator

Question 44

# **Redox Titrations** What are the half equations and full redox reaction of iodine and thiosulfate?

Answer 44

Page 421

Question 45

# **Redox Titrations** What happens to the blue color of the starch indicator?

Answer 45

It forms a blue color when it forms a complex awith I2, however this blue color disappears when is reduced to I–

Question 46

# **Redox Titration** Why is determining the dissolved oxygen quantity of water important?

Answer 46

As oxygen is essential to the survival of aquatic life. As the level of pollution in water increases, the dissolved oxygen content generally decreases

Question 47

# **Redox Titrations** What is the BOD

Answer 47

BOD is the quantity of oxygen needed to oxidize organic matter in a sample of water over a five-day period at a specified temperature.

Question 48

# **Redox Titrations** What is the Winkler method?

Answer 48

A series of redox recations which helps determine quantity of dissolved oxygen in water

Question 49

# **Redox Titrations** What is the first step of the Winkler method?

Answer 49

The dissolved oxygen, O2(g), in the water is 'fixed’ by the addition of amanganese(II) salt such as MnSO4. Reaction of this salt with O2 in basic solution causes oxidation of Mn(II) to higher oxidation states, such as Mn(IV). Page 423

Question 50

# **Redox Titrations** What is the second step of the Winkler method?

Answer 50

Acidified iodide ions, I–, are added to the solution, and are oxidized by the Mn(IV) to I2

Question 51

# **Redox Titrations** What is the third step of the Winkler method?

Answer 51

The iodine produced is then titrated with sodium thiosulfate, or every 1 mole of O2 in the water, 4 mol of S2O32– are used