Redox

Question 1

What is the oxidation number of any uncombined element ?

Answer 1

0

Question 2

What is the oxidation number of combined oxygen ?

Answer 2

-2

Question 3

What is the oxidation number of combined hydrogen ?

Answer 3

+1

Question 4

What is the oxidation number of a simple ion ?

Answer 4

the charge on the ion

Question 5

What is the oxidation number of combined fluorine ?

Answer 5

-1

Question 6

What is the oxidation number of hydrogen in a metal hydride ?

Answer 6

-1

Question 7

What is the oxidation number of oxygen in a peroxide ?

Answer 7

-1

Question 8

What is the oxidation number of oxygen when bonded to fluorine ?

Answer 8

+2

Question 9

What is the oxidation number of a transition metal ?

Answer 9

the number in the brackets

Question 10

What is oxidation in terms of electron transfer ?

Answer 10

loss of electrons

Question 11

What is oxidation in terms of oxidation number ?

Answer 11

an increase in oxidation number

Question 12

What is reduction in terms of electron transfer ?

Answer 12

gain of electrons

Question 13

What is reduction in terms of oxidation number ?

Answer 13

a decrease in oxidation number

Question 14

What is a redox reaction ?

Answer 14

a reaction that involves both oxidation and reduction

Question 15

What is an oxidising agent ?

Answer 15

a specie that oxidises another specie and itself gets reduces

Question 15

What is a reducing agent ?

Answer 15

a specie that reduces another specie and itself gets oxidised

Question 16

What is disproportionation ?

Answer 16

where the same element is oxidised or reduced in a redox reaction

Question 17

What is the reagent, observation and equation in the test for carbonate ions ?

Answer 17

• reagent : nitric acid
• observation : bubbles of gas (can be bubbles through limewater to prove it is CO2)
• 2H+ (aq) + CO3 2- (aq) => H2O (l) + CO2 (g)

Question 18

What is the reagent, observation and equation in the test for sulphate ions ?

Answer 18

• reagent : barium nitrate
• observation : white precipitate
• Ba 2+ (aq) + SO4 2- (aq) => BaSO4 (s)

Question 19

Why must you do the test for carbonates before the test for sulphates ?

Answer 19

because you can get a false positive if CO3 2- is present as barium carbonate is produced, which is insoluble

Question 20

What is the reagent, observation and equation in the test for ammonium ions ?

Answer 20

• reagent : hydroxide ions
• observation : damp red litmus paper turns blue
• NH4+ (aq) + OH- (aq) => NH3 (g) + H2O (l)

Question 21

What is the order for tests in qualitative analysis ?

Answer 21

1. carbonates
2. sulphates
3. ammonium
4. halides

Question 22

Which acid should be used for the carbonate test if you may go on to test for halides or sulphates and why ?

Answer 22

nitric acid, as you are testing for sulphates and halides, so you can’t use hydrochloric or sulphuric acid

Question 23

Why is it important to remove carbonates by adding acid before testing for sulphates ?

Answer 23

because carbonates may give a false positive when barium nitrate is added

Question 24

Which barium solution should be used for the sulphate test if you may go on to test for halides , and why ?

Answer 24

barium nitrate, as you are testing for halides so you can't use barium chloride

Question 25

Why is the halide test done last ?

Answer 25

to rule out the carbonates and sulphates first as they also give a white precipitate