T 9 REDOX

Question 1

Define oxidation (all)

Answer 1

Loss of electrons (think Zn—>Zn2+ ZnCu voltaic)
Increase in oxidation number
Gain oxygen//loss of hydrogen

Question 2

Define reduction (all)

Answer 2

Gain of electrons (think Cu2+ —> Cu ZnCu voltaic cell)
Decrease in oxidation number
(Loss oxygen//gain hydrogen)

Question 3

Why do REDOX reactions occur (in pair always oxidation and reduction)?

Answer 3

Electrons are never lost freely; if a species is oxidized, a species is also reduced

Question 4

How do you know if a reaction is a redox reaction?

Answer 4

If oxidation states change = redox
If no change of oxidation states = not redox

Answer 5

Oxidation number = Roman numerals
Oxidation state = sign in front of number

Question 6

All elements in their elemental state have an oxidation state of

Answer 6

ZERO!!

Question 7

Simple ions have oxidation state equal to

Answer 7

THEIR CHARGE

Question 8

Oxygen within a compound always has an oxidation state of

Answer 8

-2 (EXCEPT in PEROXIDES, ex H2O2; when it is -1)

Question 9

Hydrogen within a compound always has an oxidation state of

Answer 9

+1 (EXCEPT in HYDRIDES, ex NaH, when it is -1)

Question 10

The algebraic sum of all the oxidation states in a compound is

Answer 10

ZERO

Question 11

The algebraic sum of all the oxidation states in an ion (complex ion)

Answer 11

= the CHARGE OF THE ION

Question 12

What does the position of a metal/element relative to HYDROGEN in an activity series tell you?

Answer 12

Species/metals ABOVE HYDROGEN REACT W ACIDS —> H2(g)
Those BELOW hydrogen DO NOT FORM H GAS IN REACTION W ACID

Question 13

What does the position of a metal/element relative to CARBON in an activity series tell you?

Answer 13

Whether it can be reduced by carbon.
If the species/metal is BELOW C it CAN BE REDUCED (ion—>atom) BY CARBON
If it is above, it cannot (eg hydrolysis required)

For this and hydrogen: think in thirds; the particular property (forming H2 when w acid // reduces by carbon) is for those in the 2/3 part.

Question 14

Oxidation numbers/states are used for:

Answer 14

Naming of compounds
Determining whether a reaction is a redox reaction + what is oxidized/reduced
(To balance redox reactions)

Question 15

How do you balance/find equation of redox reactions?

Answer 15

Use HALF-EQUATION METHOD
Write the two half-equations
BALANCE CHARGE=ELECTRONS. OXYGEN=WATER. HYDROGEN=H+
Ensure that you have the same amount of electrons in both half equations, if not MULTIPLY THE ENTIRE HALF EQUATION to get same amount electrons
Then add the two half equations together and simplify

Question 16

Define
Oxidizing agent
Reducing agent

Answer 16

Oxidizing agent = substance that causes another substance to be oxidized, and is itself reduced

Reducing agent = substance that causes another substance to be reduced, and is itself oxidized

Question 17

What is a redox couple + example using Zinc

Answer 17

The reactant and product in one of the half-equations are known as a redox couple (comp to acid base pair)
Zn and Zn2+

Question 18

Strength of oxidizing agent in redox couple

Answer 18

If one of the species is a strong oxidising agent, the other will be a weak reducing agent and vice versa (comp to acid/base pair)

Question 19

The higher up a species is in the activity series, the more powerful

Answer 19

REDUCING AGENT, prefers to be in the oxidized state

Question 20

The lower down in the series the more powerful

Answer 20

OXIDIZING AGENT (prefers to be in the reduced state).