2.1.5 Redox

Question 1

Oxidation number of elements is always

Answer 1

Zero

Question 2

O oxidation number

Answer 2

-2 e.g in CaO, H2O

Question 3

H oxidation number

Answer 3

+1 e.g in NH3, H2S

Question 4

F oxidation number

Answer 4

-1 (e.g HF)

Question 5

Na+, K+ oxidation number

Answer 5

+1

Question 6

Mg2+, Ca2+ oxidation number

Answer 6

+2

Question 7

Cl-, Br-, I- oxidation nunber

Answer 7

-1

Question 8

What is the oxidation number of H in metal hydrides (e.g NaH, CaH2)

Answer 8

-1

Question 9

What is the oxidation number of O in peroxides (H2O2)

Answer 9

-1

Question 10

Oxidation number of O bonded to F (F2O)

Answer 10

+2

Question 11

Sum of oxidation numbers is equivalent to

Answer 11

The total charge

Question 12

Worked example using formulae using oxidation numbers

Answer 12

E.g oxidation nunber of N in NO3-

-> O = -2 so O3 is -6
Total charge = -1
-6 - - 1 = N = 5

Question 13

The roman numeral shows the […] of an element e.g for iron (II)

Answer 13

oxidation state
-> iron (II) = oxidation number +2 = Fe2+

Question 14

Nitrate (III) is NO2-. What is the oxidation number of N

Answer 14

+3

Question 15

Sulfate formula

Answer 15

SO42-

Question 16

Oxidation is terms of oxygen

Answer 16

The addition of oxygen

Question 17

Reduction in the case of oxygen

Answer 17

Removal of oxygen

Question 18

OILRIG (in terms of electrons)

Answer 18

Oxidation is loss, reduction is gain

Question 19

Redox in terms of oxidation number

Answer 19

Reduction = a decrease in oxidation number
Oxidation = an increase in oxidation number

Question 20

Reaction of Zinc with HCl

Answer 20

Zn + 2HCl -> ZnCl2 + H2

-> Zn oxidises as its number increases by 2, while H reduces.

Question 21

What is a disproportionate reaction

Answer 21

One where the same element is both oxidised and reduced