Electrochemistry

Question 1

Electronegativity is…

Answer 1

A measure of the tendency of an atom (of that element) to attract a bonding pair of electrons

Question 2

oxidation can be identified by…

Answer 2

• a loss of electrons
• an increase in oxidation number
• the gaining of oxygen
• the loss of hydrogen

Question 3

reduction can be identified by…

Answer 3

• a gain of electrons
• a decrease in oxidation number
• the loss of oxygen
• the gain of hydrogen

Question 4

redox reactions involve…

Answer 4

electron transfer

Question 5

oxidation shows electrons on the ___ side of the equation

Answer 5

RHS (R cannot go with Reduction)

Question 6

reduction reactions show electrons on the ___ side of the equation

Answer 6

LHS

Question 7

oxidants or oxidising agents are…

Answer 7

reactants that cause another substance to be oxidised

Question 8

reductants or reducing agents are…

Answer 8

reactants that cause another substance to be reduced

Question 9

explain qs for oxidants

Answer 9

a reaction with (oxidant) causes (other reactant) to lose electrons. thus, it is causing the oxidation of (other reactant)

Question 10

explain q for reducant

Answer 10

a reaction with (reductant) causes (other reactant) to gain electrons. thus, (reductant) is causing the reduction of (other reactant)

Question 11

do oxidation numbers appear as: +2, -2 or 2+, 2-?

Answer 11

+2 or -2, always the sign preceding the number

Question 12

rule one for oxidation numbers (N.O)

Answer 12

the sum of all the oxidation numbers in any substance is equal to the overall charge. this means that in elemental form, it will always have an N.O of 0.

eg. Oxygen gas = N.O of 0
      Oxide ion (2-) = N.O of -2

Question 13

rule two for oxidation numbers (N.O)

Answer 13

fluorine has an N.O of -1 in compounds

Question 14

rule three for oxidation numbers (N.O)

Answer 14

group one metals are +1 in compounds, while group 2 metals are +2 in compounds

Question 15

rule four for oxidation numbers (N.O)

Answer 15

when H is bonded to non-metals, it has an oxidation number of +1. When H is bonded to metals, it has an oxidation number of -1 (hydride ion)

Question 16

rule five for oxidation numbers (N.O)

Answer 16

oxygen usually has an oxidation number of -2 in compounds. however, in peroxides, it has an oxidation number of -1.

eg. H2O2, BaO2

Question 17

rules six and seven for oxidation numbers (N.O) - not NECESSARY

Answer 17

6. Group seven elements are usually -1 in compounds (unless a higher rule contradicts this). if two or more group seven elements are present, the more ELECTRONEGATIVE one is -1. Fluorine is the most electronegative element.
7. In the absence of other information, group 6 metals are USUALLY -2, group 5 non-metals are USUALLY -3 and group 3 metals are USUALLY +3. many transition metals have variable oxidation numbers so assign these last.

Question 18

find the oxidation number for : oxygen gas (O₂) and ammonium sulphate ((NH₄)₂SO₄)

Answer 18

oxygen gas - overall sum = 0, thus the N.O is 0
- O = 0

ammonium sulphate - sulphate has a sum of -2, O is -2 so 4 x -2 = -8, making S +6 (-8+6=-2)

                               - ammonium has a sum of +1, H is +1 so 4 x +1 = 4, making N -3 (4+-3 =+1) - S = +6, O = -2, N = -3, H = +1