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WAEC questions for "Chemistry :: Redox Reactions"
Q1

Which of the following substances is the anode in the dry Leclanche cell?

A

Carbon rod

B

Muslin bag

C

The seal

D

Zinc container

E
Q2

Consider the reaction represented by the equation: 2H2SO4(aq) + C(s) → 2H2O(l) + 2SO2(aq) + CO2(aq). H2SO4 is acting as

A

a catalyst

B

an oxidizing agent

C

a reducing agent

D

a sulphonating agent

E
Q3

Which of the following oxides of nitrogen has oxidation number of +1?

A

KNO3

B

N2O

C

N2O3

D

NO

E
Q4

In dry Leclanche cell, manganese (IV) oxide acts as

A

a reducing agent

B

binding agent

C

catalyst

D

depolarizer

E
Q5

Oxidation takes place at the electrolysis because the anode

A

is deficient in electrons

B

is deficient in protons

C

has excess electrons

D

has attraction for positive ions

E
Q6

Calculate the quantity of electricity passed when 0.4A flows for 1 hour 20 minutes through an electrolytic cell?

A

4800

B

3840

C

1920

D

32

E
Q7

Which of these cell notations is the correct representation of Daniel cell?

A

Zn(s) / Zn2+(aq) || Cu2+/Cu(s)

B

Cu(s) / Cu2+(aq) || Zn2+(aq) / Zn(s) 

C

Zn2+(aq) / Zn(s) || Cu(aq) / Cu(s)

D

Cu2+(aq) / Cu(s) || Zn(s) /Zn2+(aq)(

E
Q8

Which species undergo reduction in the reaction represented by the equation below?

H2S(aq) + 2FeCl3(aq) → S(s) + 2HCl(aq) + 2FeCl2(aq)

A

Fe3+

B

H2S

C

Cl-

D

S

E
Q9

What is the oxidation number chromium in K2CrO4?

A

+1

B

+2

C

+4

D

+6

E
Q10

What is the product formed at the cathode during the electrolysis of concentrated sodium chloride solution using carbon electrodes?

A

Chlorine

B

Hydrogen

C

Oxygen

D

Sodium

E
Q11

Electrolysis is applied in the following processes except

A

electroplating

B

extraction of aluminium

C

extraction of iron

D

purification of copper

E
Q12

The oxidation number of  iodine in the iodate ion (IO3-) is

A

-5

B

-1

C

+1

D

+5

E
Q13

Consider the reaction: 2Al(s) + 6H+(aq) → 2Al3+(aq) + 3H2(g) . What is the total number of moles of electrons transferred from aluminium atoms to the hydrogen ions?

A

3

B

4

C

5

D

6

E
Q14

In the reaction represented by the equation:

5Fe2+(aq) + MnO-4(aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+4(aq) + 4H2O(l). Which species is reduced?

A

Fe2+

B

MnO-4

C

H+

D

Fe3+

E
Q15

In which of the following reactions is sulphur (IV) oxide acting as an oxidizing agent?

A

2HNO3(aq) + SO2(g) → H2SO4(aq) + 2NO2(g)

B

2KMnO4(aq) + 5SO2(aq) + 2H2O(l) → K2SO4(aq) + MnSO4(aq) + 2H2SO4(aq)

C

FeCl3(aq) + SO2(g) + 2H2O(l) → FeCl2(aq) + 2HCl(g) + H2SO4(aq)

D

2H2S(g) + SO2(g) → 2H2O(l) + 3S(s)

E
Q16

Which of the following equations represent a redox reaction?

A

Pb(NO3)2(aq) + 2HCl → PbCl3 + 2HNO3(aq)

B

H2S(g) + Cl2(g) → 2HCl(g) + S(s)

C

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

D

BaCl2(aq) + K2SO4(aq) → BaSO4(s) + 2KCl

E
Q17

The main difference between a primary cell and a secondary cell is that the primary cell

A

The primary is an electrolytic cell but the secondary is not

B

cannot be recharged the secondary cell can

C

can be recharged but the secondary cell cannot

D

contains the electrodes but the secondary cell does not

E
Q18

What is the reducing agent in the reaction represented by the following equation?

Fe3+(aq) + H2S(g) → 2Fe2+(aq) + 2H+(aq) + S(s)

A

Fe3+(aq)

B

H2S(g)

C

Fe2+(aq)

D

S(s)

E
Q19

The reaction that takes place at the cathode when a aqueous solution of NaCl is electrolysed using carbon electrodes is

A

2H-(aq) + 2e- → H2(g)

B

Na+(aq) + e- → Na(s)

C

4OH → 2H2O2(l) + O2(g) + 4e-

D

2Cl- → Cl2(g) + 2e-

E
Q20

Consider the cell represented below.

Zn/Zn2+(aq) // Cu2+(aq)/Cu(s) .Which of the following statements is correct about the cell?

 

A

Zn is oxidized to Zn2+

B

Cu is oxidized to Cu2+

C

It is an electrolytic cell

D

Each single line represents a salt bridge

E
Q21

Consider the following electronegativity values:
H W X Y Z
2.1 1.2 1.5 2.1 3.5
Which of the elements represented by the letters W to Z will combine with hydrogen (H) to form a purely covalent compound?

 

 

 

A

W

B

X

C

Y

D

Z

E
Q22

Which is the change in the oxidation number of of I- in the reaction represented by the following equation?

5I-(aq) + 6H+(aq) + 10-3(aq) → 3I2(g) + 3H2O(l)

A

-5 to -3

B

-1 to 0

C

+5 to +3

D

-1 to +2

E
Q23

Consider the electrochemical cell represented below. Zn(s)/Zn2+(aq)//Cu2+(aq)/Cu(s) .Which of the following equations describes the reaction occuring in the cell?

A

Cu(s) + Zn2+(aq) → Cu2+(aq)

B

Cu(s) + Zn2+(s) → Cu2+(aq) + Zn2+(aq)

C

Zn(s) + Cu2+(aq) → Zn2+(s) + Cu(s)

D

Zn2+(aq) + Cu2+(aq) → Zn(s) + Cu(s)

E
Q24

Which of the metals is most likely extracted by electrolysis of its fused chloride?

A

V

B

W

C

X

D

Y

E
Q25

Which of the following statements is/are correct about tin plating?

I.  The electrolyte must be a soluble salt of tin

II  The object to be plated is made the cathode

III The anode is made of tin

IV  The negative electrodes dissolves

A

I only

B

I and II only

C

I, II, III only

D

I, II and IV only

E
Q26

What is the product at the positive electrodes

A

Lead

B

Oxygen

C

Hydrogen

D

Bromine

E
Q27

Determine the amount of electrons needed to deposit 6.4g of copper during the electrolysis of copper (II) tetraozosulphate (VI) solution [Cu = 64]

A

0.10mole

B

0.20mole

C

1.0mole

D

2.0mole

E
Q28

The equation for the reaction at the anode during the electrolysis of concentrated sodium chloride solution is

A

2Cl-(aq) → Cl2(g) + 2e-

B

4OH-(aq) → 2H2O(l) + O2(g) + 4e-

C

Na+(aq) + e- → Na(s)

D

2H+(aq) + 2e- → H2(g)

E
Q29

Consider the following equation: Cr2O72-(aq) + 14H+(aq) + 6e- → 2Cr3+(aq) + 7H2O(l). The oxidation number of chromium changes from

A

-2 to +3

B

-2 to +6

C

+6 to +3

D

+7 to +6

E
Q30

Which of the following ions require the largest quantity of electricity for discharge at an electrode?

A

2.0 mole of Q3+

B

2.5 mole of R2+

C

3.0 mole T-

D

4.0 mole of Y-

E
Q31

If two metallic ions of the same concentration migrate to a graphite cathode, the one that would be preferentially discharged is the one that has the

A

smaller mass

B

lower electrical charge

C

greater stability in solution

D

stronger tendency to accept electrons

E
Q32

When conentrated sodium chloride is electrolysed using inert electrodes, the products are

A

oxygen and hydrogen

B

hydrogen and chlorine

C

sodium and oxygen

D

sodium and chlorine

E
Q33

What is the oxidation number of nitrogen in Al(NO3)3?

A

+1

B

+3

C

+5

D

+6

E
Q34

What is oxidized in the reaction represented by the following equation?

3Cu + 8HNO3 → 3Cu(NO3)2 + 2NO + 4H2O

A

Oxygen

B

Hydrogen

C

Nitrogen

D

Copper

E
Q35

Which of the following ssubstances decomposes when an electric current is passed through it?

A

Glucose solution

B

Zinc rod

C

Hydrochloric acid

D

Tetrachloromethane

E
Q36

A concentrated solution containing H+, Cu2+, OH- and Cl- was electrolyzed using platinum electrodes. Which of the ions will be discharged at the cathode?

A

H+

B

Cu2+

C

OH-

D

Cl-

E
Q37

In the electrolysis of CuSO4 using copper electrodes, the reaction of the anode is

A

discharge of SO42-

B

discharge of OH-

C

dissoution of copper electrodes

D

evolution of oxygen

E
Q38

A feasible cell was constructed by joining the two half celss thus:

Cu2+(aq) + 2e- → Cu(s) Eo = +0.34V;  Zn2+(aq) + 2e- → Zn(s) Eo = -0.76V. What is the standard of e.m.f of the cell?

A

-1.1V

B

-0.42V

C

+0.42V

D

+1.1V

E
Q39

In which of the following is the oxidation number of sulphur equal to -2?

A

S8

B

H2S

C

SO2

D

SO32-

E
Q40

An iron nail placed in solution of copper (II) tetraoxosulphate (VI) is soon covered with a deposit of copper. Which of the following equations represents the reaction?

A

Fe2+(aq) + Cu(s) → Fe3+(aq) + Cu2+(aq)

B

Fe2+(aq) + Cu(s) → Fe(aq) + Cu2+(aq)

C

Fe(s) + Cu2+(aq) → Fe2+(aq) + Cu2+(aq)

D

Fe(s) + Cu2+(aq) → Fe2+(aq) + Cu(s)

E
Q41

0.10 mole dm-3 NaCl conducts electricity better than o.10 mole dm-3 CH3COOH because the solution of NaCl

A

contains more ions

B

is neutral to litmus

C

has a lower molar mass

D

has a higher pH

E
Q42

Which of the following occurs when a solution of CuSO4 is electrolysed using copper electrodes?

A

The cathode becomes coated with copper

B

Both electrodes gain electrons

C

The blue colour of the solution fades gradually

D

The anode increases in mass

E
Q43

Which of the following is not correct about oxidation number convention? The oxidation number of a/an

A

element in the free state is zero

B

monoatomic ion is equal to its charge

C

alkali metals like sodium in its compound is +1

D

atom of a diatomic molecule is +2

E
Q44

When dilute copper (II) chloride solution is electrolysed, the reaction at the cathode is represented by the equation:

A

Cu → Cu2+ + 2e-

B

Cu2+ + 2e- → Cu

C

4OH- + 4e- → O2 + 2H2O

D

2Cl- → Cl2 + 2e-

E
Q45

The set-up shown in the diagram represents a/an

A

Secondary cell

B

Electrochemical cell

C

Daniel cell

D

elctrolytic cell

E
Q46

The bulb in the set-up will not light if K is

A

Molten sodium chloride

B

acidified water

C

tetrachloromethane

D

Ethanoic acid

E
Q47

A metal which can be used as sacrificial anode for preventing corrosion of iron pipe is

A

copper

B

magnesium

C

silver

D

lead

E
Q48

What is the function of sulhpur (IV) oxide in the reaction represented by the following equation?

SO2(g) + 2H2S(g) → 3S(g) + 2H2O(l)

A

Dehydrating agent

B

Oxidizing agent

C

Bleaching agent

D

Acid

E

Precipitant

Q49

Which of the following will produce oxygen and hydrogen during its electrolysis using plantinum electrode?

A

Glucose solution

B

Aqueous copper (II) tetraoxosulphate (VI)

C

Dilute sodium chloride solution

D

Concentrated hydrochloric acid

E

Dilute copper (II) chloride solution

Q50

How many electrons are removed from Cr2+ when it is oxidized to CrO42-?

A

0

B

2

C

4

D

8

E

10

Q51
Rusting of iron is an example of
A
deliquescence
B
decomposition
C
displacement reaction
D
redox reaction
E
reversible reaction
Q52

Which of the following is/are manufactured by electrolysis?

I   Calcium

II  Chlorine

III Aluminium

IV  Iron

A

IV

B

I and II

C

III and IV

D

I, II and III

E

I, II, III and IV

Q53
The factors which affect the preferential discharge of ions during electrolysis include I . protons in the nucleus II unpaired electrons III relative position in the electrochemical series IV charge on the ions
A
IV
B
I and II
C
III and iV
D
I, II and III
E
I, II, III and IV
Q54

Which of the following will migrate to the cathode during electrolysis?

A

Zinc ions

B

Chloride ions

C

Sulphide ions

D

Tetraoxosulphate (VI) ions

E

Trioxonitrate (V) ions

Q55

The common feature of reaction at the anode is that

A

electrons are consumed

B

oxidation is involved

C

ions are reduced

D

the electrodes dissolves

E

the electrolyte is diluted

Q56

Which of the following metals is not extracted by electrolysis?

A

Iron

B

Sodium

C

Calcium

D

Magnesium

E

Aluminium

Q57

Amphoteric oxides are oxides which

A

react with water to form acids

B

react with water to form alkali

C

show neither acidic or basic properties

D

react with both acids and alkalis

E

contain high proportion of oxygen

Q58

In which of the following compounds is the oxidation number of nitrogen equal to +3?

A

NO3

B

N2O

C

NO

D

HNO2

E

HNO3

Q59

Which of the following statements is not correct about electrolysis?

A

Reduction occurs in the anode

B

Anions migrate to the anode

C

Positive ions migrate to the cathode

D

Concentration affects the discharge of ions

E

Electrolytes conducts electric current

Q60

When acidified KmnO4 solution is decolorised by ethene, the gas the acts as

A

a straight-chain hydrocarbon

B

a saturated hydrocarbonate

C

a reducing agent

D

a dehydrating agent

E

an oxidizing agent