Ch. 11: Oxidation-Reduction Reactions (Complete)

Question 1

defn: oxidation-reduction (redox) reactions

Answer 1

reactions that involve the transfer of electrons from one chemical species to another

Question 2

defn: the law of conservation of charge

Answer 2

electrical charge can be neither created nor destroyed

Question 3

why can an isolated loss or gain of electrons never occur?

Answer 3

because of the law of conservation of charge

Question 4

defn: redox reaction

Answer 4

an electron transfer that comes as a result of simultaneous oxidation (loss of electrons) and reduction (gain of electrons)

Question 5

defn: oxidizing agent
defn: reducing agent

Answer 5

oxidizing agent: causes another atom in a redox reaction to undergo oxidation and is itself reduced

reducing agent: causes the other atom to be reduced and is itself oxidized

Question 6

redox reaction mnemonic:

Answer 6

LEO the lion says GER: Loss of Electrons is Oxidation, Gain of Electrons is Reduction

OIL RIG is a mnemonic for the SAME
Oxidation Is Loss of electrons, Reduction Is Gain of electrons

Question 7

what do almost all oxidizing agents contain?

Answer 7

oxygen or another strongly electronegative element (such as a halogen)

Question 8

what do reducing agents contain?

Answer 8

metal ions or hydrides (H-)

Question 9

True or False: Sometimes texts will describe the compound as a whole as the oxidizing or reducing agent

Answer 9

True (CrO3, rather than Cr6+)

Question 10

func: oxidation numbers

Answer 10

assigned to atoms in order to keep track of the redistribution of electrons during chemical reactions

Question 11

what are the 8 oxidation number assignment rules?

Answer 11

the oxidation number . . .

1. of a free element is zero
2. for a monatomic ion is equal to the charge of the ion
3. of each Group IA element in a compound is +1
4. of each Group IIA element in a compound is +2
5. of each Group VIIA element in a compounds is -1, except when combined with an element of higher electronegativity
6. of hydrogen is usually +1; however, its oxidation number is -1 in compounds with less electronegative elements
7. of oxygen is -2, in most compounds
8. the sum of the oxidation numbers of all the atoms present in a neutral compound is zero. the sum of the oxidation numbers present in a polyatomic ion is equal to the charge of the ion.

Question 12

what is convention for order of cation and anion in a compound?

Answer 12

Cation first, anion second

Question 13

what is similar and different between oxidation number and formal charge?

Answer 13

both account for the perceived charge on an element, but they do so in different ways

oxidation number assumes unequal division of electrons in bonds, “awarding” the electrons to the more electronegative element

formal charge assumes equal division of electrons in bonds, “awarding” one electron to each atom in the bond

Question 14

where should you start when assigning oxidation numbers?

Answer 14

start with the known atoms, which are usually groups I and II, halides, and oxygen

Question 15

do transition metals have one or more than one oxidation states? why?

Answer 15

transition metals can take on multiple oxidation states

when transition metals are oxidized or reduced, the absorption and emission of light from a metal is altered such that different frequencies are absorbed

changes of oxidation state in transition metals usually correspond to a color change

Question 16

what two things must be balanced when balancing a redox reaction?

Answer 16

the net charge
the number of atoms

Question 17

defn + aka: half-reaction method

Answer 17

aka: ion-electron method

the equation is separated into two half-reactions, the oxidation part and the reduction part

each half-reaction is balanced separately, and they are then added to give a balanced overall reaction

Question 18

defn: complete ionic equation

Answer 18

we split the various species into all of the ions present

Question 19

defn: spectator ions

Answer 19

species that are present on both sides of the equation in the same form, are chemically inert within the reaction

they do not take part in the overall reaction but simply remain in the solution unchanged

Question 20

defn: net ionic equation

Answer 20

shows only the species that actually participate in the reaction (no spectator ions)

Question 21

what should you do with aqueous compounds, solid salts when writing net ionic equations?

Answer 21

aqueous compounds: split into their constituent ions

solid salts: keep together as a single entity

Question 22

defn: combination reaction

Answer 22

two or more species come together to form a product

Question 23

defn: decomposition reaction

Answer 23

one product breaks down into two or more species

Question 24

defn: combustion reactions

Answer 24

a fuel (usually a hydrocarbon) is mixed with an oxidant (usually oxygen), forming carbon dioxide and water

Question 25

defn + aka: double-displacement reactions

Answer 25

aka: metathesis reactions

involve the switching of counterions

Question 26

why are double-displacement reactions not usually redox reactions?

Answer 26

because all ions generally retain their oxidation state

Question 27

in double-displacement reactions where both reactants and both products are aqueous, is there a net ionic reaction? why or why not?

Answer 27

no, because all of the ions appear on both sides of the reaction

Question 28

defn + aka + use: disproportionation

Answer 28

aka: dismutation

a specific type of redox reaction in which an element undergoes both oxidation and reduction in producing its products

used by many biological enzymes

Question 29

what is the main difference between acid-base titrations and redox titrations?

Answer 29

acid-base titrations follow the movement of protons

redox titrations follow the transfer of charge (as electrons) to reach the equivalence point

Question 30

what are two unique aspects of the indicators that redox titrations use?

Answer 30

they change color at a particular voltage (emf) value

they have different colors in their oxidized and reduced forms

Question 31

defn + func: potentiometric titration

Answer 31

a form of redox titration where no indicator is used

instead, the electrical potential difference (voltage) is measured using a voltmeter

as a redox titration progresses, its voltage changes

Question 31

defn + what does it rely on + process: iodimetric titration

Answer 31

a prototypical redox titration which involves the use of starch indicators to identify iodine complexes

it relies on the titration of free iodine radicals

the presence of iodine is initially determined by a dark solution in the presence of starch, and at the endpoint of the titration, a colorless solution develops

Question 32

what is potentiometric titration analogous to in acid-base titration?

Answer 32

acid-base titration with a pH meter instead of a color indicator