Ch 11 - Oxidation Reduction Reactions

Question 1

What is the difference between oxidation and reduction and makes a redox reaction?

Answer 1

• oxidation is a loss of electrons
• reduction is a gain of electrons
• the 2 are paired together to make a redox reaction

Question 2

What are oxidizing and reducing agents?

Answer 2

• oxidizing facilitates the oxidation of another compound and is reduced itself in the process - tendency to gain electrons - (almost all contain oxygen or a similar electronegative element - O2, H2O2, halogens, H2So4, HNO3, NaClO, PCC, NAD+, FADH)
• reducing facilitates the reduction of another compound and is itself oxidized in the process (often contain metal ions or hydrides (H-) - CO, C, B2H6, LiAlH4)

Question 3

How are oxidation numbers assigned?

Answer 3

• any free element or diatomic species has an ON of 0
• ON of a monatomic ion is equal to the charge of the ion
• when in compounds, group 1 metals have an ON of +1; group 2 metals have an ON of +2, group 7 have ON of -1 (unless combined with an element with higher electronegativity)
• ON of H is +1 unless it is paired with a less electronegative element, in which case it is -1
• ON of oxygen is -2, except in peroxides (when its charge is -1) or in compounds with a more electronegative element
• the sum of the ON of all the atoms in a compound is equal to the overall charge of the compound

Question 4

How are redox reactions balanced?

Answer 4

using the half-reaction method (ion-electron method)

• separate the 2 half reactions
• balance the atoms of each half reaction; start with all the elements besides H and O (in acidic solution balance H and O using H+; use OH- in basic solution)
• balance the charges of each half reaction by adding electrons as necessary to one side of the reaction
• multiply the half reactions as necessary to obtain the same number of electrons in both half reactions
• add the half reactions, cancelling out terms on both sides of the reaction
• confirm that the mass and charges are balanced

Question 5

What do complete ionic equations account for and how are they written?

Answer 5

• account for all the ions present n a reaction

- to write, split all aqueous compounds into their relevant ions, keep solid salts intact

Question 6

What do net ionic equations do differently than complete equations?

Answer 6

• ignore spectator ions to focus only on the species that actually participate in the reaction
• to obtain, subtract the ions appearing on both sides of the reaction (spectator ions)

Question 7

What is the net ionic equation for reactions that contain no aqueous salts?

Answer 7

generally the same as the overall balanced reaction

Question 8

What is the net ionic equation for double displacement (metathesis) reactions that do not form a solid salt?

Answer 8

there is no net ionic reaction because all ions remain in solution and do not change oxidation number

Question 9

What are disproportionate (dismutation) reactions?

Answer 9

a type of redox reaction in which one element is both oxidized and reduced, forming at least 2 molecules containing the element with different oxidation states

Question 10

What are oxidation-reduction titrations?

Answer 10

• similar to acid-base titration
• follow transfer of charge
• indicators used change color when certain voltages of solutions are achieved

Question 11

What are potentiometric titrations?

Answer 11

• a form of redox titration in which a voltmeter or external cell measures the electromotive force (emf) of a solution
• no indicator is used and the equivalence point is determined by a sharp change in voltage