electrolysis

Question 1

During the electrolysis of molten lead bromide, which of the following takes place :
A : Bromine is released at the cathode. B: Lead is deposited at the anode.
C : Bromine ions gain electrons. D: Lead is deposited at the cathode

Answer 1

D.

Question 2

Here is an electrode reaction : Cu → Cu2+ + 2e-. [i.e. Cu- 2e- →Cu2+]. At which electrode(anode or cathode) would such a reaction take place. Is this an example of oxidation or reduction.

Answer 2

• At anode. Oxidation.

Question 3

` A solution contains magnesium ions(Mg2+), iron (II) ions (Fe2+) and copper ions (Cu2+). On passing an electric current through this solution which ions will be the first to be discharged at the cathode. Write the equation for the cathode reaction.

Answer 3

• Mg2+

Question 4

An electrode ‘A’ is connected to the positive terminal of a battery and electrode ‘B’ to the negative terminal.

(i) Give the names of the electrodes A & B.
(ii) Which electrode is the oxidizing electrode.

Answer 4

(i) A – Anode, B – Cathode. (ii) A.

Question 5

State the appropriate term used for : – A liquid or solution, which conducts electricity with accompanying chemical change.

Answer 5

• Electrolytes.

Question 6

Electrons are getting added to an element Y.

(i) Is Y getting oxidized or reduced?
(ii) What charge will Y have after the addition of electrons?
(iii) Which electrode will Y migrate to during electrolysis?

Answer 6

(i) Reduced (ii) Negative (iii) Anode

Question 7

`

Explain how electrolysis is an example of redox reaction.

Answer 7

• A redox reaction is one in which reduction and oxidation occurs simultaneously.
  (i) Cathode (Reducing electrode) : – At cathode, the cations gain electrons to form neutral atoms. As electrons are gained, the ion is said to be reduced.
  (ii) Anode (Oxidizing electrode) : – At anode, the anions lose electrons to form neutral atoms. As electrons are lost, the ion is said to be oxidized.

Question 8

What kind of particles will be found in a liquid compound which is a non-electrolyte?

Answer 8

Molecules.

Question 9

Complete the sentence by choosing the correct words – Electrolysis is the passage of ………… [electricity / electrons] through a liquid or a solution accompanied by a …………. [physical / chemical] change.

Answer 9

Electricity, Chemical.

Question 10

Name a liquid which is a non-electrolyte.

Answer 10

Alcohol.

Question 11

Name one substance which contains : (i) ions only (ii) molecules only (iii) both ions and molecules.

Answer 11

(i) NaOH (ii) Alcohol (iii) NaCO3.

Question 12

What is meant by the term ‘electrolyte’.

Answer 12

Chemical compounds which conduct electricity either in a fused or in aq. solution state and undergo chemical decomposition due to the flow of current through it are called electrolytes.

Question 13

What are the particles present in a compound which is non-electrolyte?

Answer 13

Molecules only.

Question 14

If an electrolyte is described as a ‘strong electrolyte’, what does this mean

Answer 14

(a) They are electrolytes which allow a large amount of electricity to flow through them and hence are good conductors of electricity.
(b) Are almost completely dissociated in fused or aqueous solution state.
(c) The solution contains almost only free mobile – ions.

Question 15

Explain why (i) solid sodium chloride does not allow electricity to pass through. (ii) copper, though a good conductor of electricity , is a non-electrolyte.

Answer 15

(i) In sodium chloride, Na+ and Cl - ions are not free to carry the electric current.
(ii) Copper metal is solid and has no mobile ions whereas an electrolyte should dissociate into oppositely charged ions to conduct the electric current.

Question 16

Classify the following substances under three headings: (i) Strong Electrolytes (ii) Weak Electrolytes (iii) Non Electrolytes – Acetic acid, ammonium chloride, ammonium hydroxide, carbon tetrachloride, dilute hydrochloric acid, sodium acetate, dilute sulphuric acid.

Answer 16

(i) Strong Electrolytes – Ammonium chloride, dilute hydrochloric acid, dilute sulphuric acid.
(ii) Weak Electrolytes – Ammonium hydroxide, acetic acid.
(iii) non Electrolytes – Carbon tetrachloride.

Question 17

As we descend the electrochemical series containing cations, the tendency of the cations to get _________ [oxidized / reduced] at the cathode increases.

Answer 17

reduced

Question 18

The [higher / lower] _________ the concentration of an ion in a solution, the greater is the probability of its being discharged at its appropriate electrode.

Answer 18

higher

Question 19

Name a solid which undergoes electrolysis when molten.

Answer 19

Lead bromide.

Question 20

What should be the physical state of lead bromide if it is to conduct electricity?

Answer 20

Molten state.

Question 21

What particles are present in pure lead bromide? Write the equations for the reactions which take place at the electrodes during the electrolysis of lead bromide.

Answer 21

Lead ions and Bromide ions.
At cathode Pb²⁺ + 2e^- → Pb
At anode 2Br^--1 – 2e^- → 2[Br]
2[Br] → Br₂ ↑

Question 22

Supply the word [or words] that will make the sentence into a correct statement which is to be written down again completely : - The electrolysis of lead bromide liberates lead and bromine.

Answer 22

The electrolysis of molten lead bromide liberates lead and bromine.

Question 23

If the compound formed between X [a metal with valency 2] and Y [a non-metal with valency 3] is melted and an electric current passed through the molten compound , the element X will be obtained at the ________ and Y at the _______ of the electrolytic cell. [Provide the missing words.]

Answer 23

Cathode, Anode

Question 24

Write the equations of the reactions which take place at the cathode and anode when acidified water is electrolyzed.

Answer 24

At cathode 2H⁺ + 2e^-- → 2H → H₂.
At anode 2OH- – 2e- → 2OH → H2O + O
O + O → O2.

Question 25

Name the gas released at the cathode when acidulated water is electrolyzed.

Answer 25

Hydrogen

Question 26

Copy and complete the following sentence: With platinum electrodes hydrogen is liberated at the ________ and oxygen at the _________ during the electrolysis of acidified water.

Answer 26

Cathode, Anode

Question 27

When the electrolysis of acidified water is carried out: [1] What is the ratio of the volume of hydrogen produced to the volume of oxygen. [2] Give the equation for the discharge of ions at the cathode.

Answer 27

[1]

2 : 1.

[2]

H+ + e- → [H]
2[H] → H2.

Question 28

(i) If HX is a weak acid, what particles will be present in its dilute solution apart from those of water.

Answer 28

Non-ionized molecules : H+ and X -.

Question 29

Pure water consists almost entirely of ______ (ions / molecules)

Answer 29

Molecules

Question 30

We can expect that pure water ________ (will / will not) normally conduct electricity.

Answer 30

will not

Question 31

To carry out the so-called “electrolysis of water”, sulphuric acid is added to water. How does the addition of sulphuric acid produce a conducting solution.

Answer 31

Sulphuric acid ionizes to form ions.

Question 32

State what is observed when copper sulphate solution is electrolyzed using a platinum anode.

Answer 32

Blue colour of the solution disappears.

Question 33

What ions must be present in a solution used for electroplating a particular metal.

Answer 33

Metal ions of the metal with which electroplating is done.

Question 34

A solution of silver nitrate is a good electrolyte but it is not used for electroplating an article with silver.

Answer 34

Because electroplating is not uniform due to very fast reaction.

Question 36

Choosing only words from the following list write down the appropriate word to fill in the blanks below : -
‘anions, anode, cathode, cations, electrode, electrolyte, nickel, voltameter’.
To electroplate an article with nickel requires an (a) ________ which must be a solution containing (b) ________ ions. The article to be plated is placed as the (c) ________ of the cell in which the plating is carried out. The (d) ________ of the cell is made from pure nickel. The ions which are attracted to the negative electrode and discharged are called (e) _______ .

Answer 36

(a) Electrolyte (b) Nickel (c) Cathode (d) Anode (e) Cations.

Question 37

Select the correct compound from the list – Ammonia, Copper oxide, Copper sulphate, Hydrogen chloride, Hydrogen sulphide, Lead bromide – which matches with the description given below : (i) A solution of this compound is used as the electrolyte when copper is purified.

Answer 37

Copper sulphate

Question 38

When the compound is electrolyzed in the molten state, lead is obtained at the cathode.

Answer 38

Lead bromide.

Question 39

Write two applications of electrolysis in which the anode diminishes in mass.

Answer 39

(i) Electroplating of an article (ii) Electro-refining of metals.

Question 40

The following questions refer to the electrolysis of copper sulphate solution with copper electrodes :
(i) Compare the change in mass of the anode

Answer 40

(i) Anode diminishes in mass.

Question 41

(ii) What is seen to happen to the colour of the copper sulphate solution if platinum electrodes are used? Explain this observation.

Answer 41

(ii) The colour of the solution fades since the blue Cu2+ ions which are discharged at the cathode are not replaced or added at the anode.

Question 42

(iii) What is the practical application of the electrolysis of copper sulphate solution? Briefly describe one such application.

Answer 42

(iii) Electro-refining of impure copper. The pure copper metal dissolves out from the copper anode [impure copper block] and the Cu2+ions formed in solution at the anode are deposited at the cathode [the thin pure sheet of copper]. The impurity present in impure copper anode settle down as anode mud or slime which contains insoluble gold and silver. Impurities such as iron, zinc etc ionize and dissolve in the electrolytic copper sulphate solution.

Question 43

A. non-electrolyte.
B. strong electrolyte.
C. weak electrolyte.
D. metallic conductor.
(i) Molten ionic compound.
(ii) Carbon tetrachloride.
(iii) An aluminium wire.
(iv) A solution containing solvent molecules, solute molecules and ions formed by the dissociation of solute molecules.
(v) A sugar solution with sugar molecules and water molecules.

Answer 43

(i) B (ii) A (iii) D (iv) C (v) A.

Question 44

(i) Here is an electrode reaction:
Cu → Cu2+ + 2e.
At which electrode (anode or cathode) would such a reaction take place? Is this an example of oxidation or reduction?
(ii) A solution contains magnesium ions (Mg2+) iron (II) ions (Fe2+) and copper ions (Cu2+). On passing an electric current through this solution which ions will be the first to be discharged at the cathode? Write the equation for the cathode reaction.
(iii) Why is carbon tetrachloride, which is a liquid, a non-electrolyte?

(i) The reaction take place at anode. This is an example of oxidation.
(ii) Mg2+.
(iii) Carbon tetrachloride is a covalent compound and do not undergo chemical decomposition due to the flow of current through it.

Answer 44

(i) The reaction take place at anode. This is an example of oxidation.
(ii) Mg2+.
(iii) Carbon tetrachloride is a covalent compound and do not undergo chemical decomposition due to the flow of current through it.

Question 45

(i) Define the term ‘catenation’.

Answer 45

(i) Catenation is defined as the tendency of an element to form chains of identical atoms.

Question 46

An electrode ‘A’ is connected to the positive terminal of a battery and electrode ‘B’ to the negative terminal.

Answer 46

i) A – Anode, B – Cathode.

Question 47

(i) Give the names of the electrodes A & B.

Answer 47

i) A.

Question 48

State the appropriate term used for : – A liquid or solution, which conducts electricity with accompanying chemical change.

Answer 48

Electrolytes.

Question 49

Electrons are getting added to an element Y.

(i) Is Y getting oxidized or reduced?
(ii) What charge will Y have after the addition of electrons?
(iii) Which electrode will Y migrate to during electrolysis?

Answer 49

i) Reduced
(ii) Negative
(iii) Anode.

Question 50

Explain how electrolysis is an example of redox reaction.

Answer 50

A redox reaction is one in which reduction and oxidation occurs simultaneously.

(i) Cathode (Reducing electrode) : At cathode, the cations gain electrons to form neutral atoms. As electrons are gained, the ion is said to be reduced.
(ii) Anode (Oxidizing electrode) : At anode, the anions lose electrons to form neutral atoms. As electrons are lost, the ion is said to be oxidized.

Question 51

What kind of particles will be found in a liquid compound which is a non-electrolyte?

Answer 51

Molecules.

Question 52

Complete the sentence by choosing the correct words – Electrolysis is the passage of ………… [electricity / electrons] through a liquid or a solution accompanied by a …………. [physical / chemical] change.

Answer 52

Electricity, Chemical

Question 53

Name a liquid which is a non-electrolyte.

Answer 53

Alcohol.

Question 54

Name one substance which contains : (i) ions only (ii) molecules only (iii) both ions and molecules.

Answer 54

(i) NaOH
(ii) Alcohol
(iii) NaCO3

Question 55

i) What is meant by the term ‘electrolyte’.

Answer 55

(i) Chemical compounds which conduct electricity either in a fused or in aq. solution state and undergo chemical decomposition due to the flow of current through it are called electrolytes.

Question 56

What are the particles present in a compound which is non-electrolyte?

Answer 56

Molecules only.

Question 57

If an electrolyte is described as a ‘strong electrolyte’, what does this mean.

Answer 57

(a) They are electrolytes which allow a large amount of electricity to flow through them and hence are good conductors of electricity.
(b) Are almost completely dissociated in fused or aqueous solution state.
(c) The solution contains almost only free mobile – ions.

Question 58

. Explain why

(i) solid sodium chloride does not allow electricity to pass through.

Answer 58

In sodium chloride, Na+ and Cl- ions are not free to carry the electric current.

Question 59

opper, though a good conductor of electricity , is a non-electrolyte.

Answer 59

Copper metal is solid and has no mobile ions whereas an electrolyte should dissociate into oppositely charged ions to conduct the electric current.

Question 60

Classify the following substances under three headings: (i) Strong Electrolytes (ii) Weak Electrolytes (iii) Non Electrolytes – Acetic acid, ammonium chloride, ammonium hydroxide, carbon tetrachloride, dilute hydrochloric acid, sodium acetate, dilute sulphuric acid.

Answer 60

`

(i) Strong Electrolytes – Ammonium chloride, dilute hydrochloric acid, dilute sulphuric acid.
(ii) Weak Electrolytes – Ammonium hydroxide, acetic acid.
(iii) non Electrolytes – Carbon tetrachloride.

Question 61

As we descend the electrochemical series containing cations, the tendency of the cations to get _________ [oxidized / reduced] at the cathode increases.

Answer 61

reduced

Question 62

The [higher / lower] _________ the concentration of an ion in a solution, the greater is the probability of its being discharged at its appropriate electrode.

Answer 62

higher.

Question 63

Name a solid which undergoes electrolysis when molten.

Answer 63

Lead bromide

Question 64

What should be the physical state of lead bromide if it is to conduct electricity?

Answer 64

Molten state.

Question 65

What particles are present in pure lead bromide? Write the equations for the reactions which take place at the electrodes during the electrolysis of lead bromide.

Answer 65

Lead ions and Bromide ions.

At cathode Pb2+ + 2e- → Pb

At anode 2Br-1 – 2e- → 2[Br]

2[Br] → Br2 ↑

Question 66

Supply the word [or words] that will make the sentence into a correct statement which is to be written down again completely : - The electrolysis of lead bromide liberates lead and bromine.

Answer 66

The electrolysis of molten lead bromide liberates lead and bromine.

Question 67

If the compound formed between X [a metal with valency 2] and Y [a non-metal with valencY 3] is melted and an electric current passed through the molten compound , the element X will be obtained at the ________ and Y at the _______ of the electrolytic cell. [Provide the missing words.]

Answer 67

Cathode, Anode.

Question 68

Write the equations of the reactions which take place at the cathode and anode when acidified water is electrolyzed.

Answer 68

At cathode 2H+ + 2e- → 2H → H2.

At anode 2OH- – 2e- → 2OH → H2O + O

O + O → O2.

Question 69

Name the gas released at the cathode when acidulated water is electrolyzed.

Answer 69

Hydrogen.

Question 70

Copy and complete the following sentence: With platinum electrodes hydrogen is liberated at the ________ and oxygen at the _________ during the electrolysis of acidified water.

Answer 70

Cathode, Anode.

Question 71

When the electrolysis of acidified water is carried out: [1] What is the ratio of the volume of hydrogen produced to the volume of oxygen. [2] Give the equation for the discharge of ions at the cathode.

Answer 71

[1] 2 : 1.

[2] H+ + e- → [H]

2[H] → H2.

Question 72

f HX is a weak acid, what particles will be present in its dilute solution apart from those of water.

.

Answer 72

Non-ionized molecules : H+ and X- .

Question 73

(ii) Write down the words or phrase from the brackets that will correctly fill in the blanks in the following: (1) Pure water consists almost entirely of ______ (ions / molecules). (2) We can expect that pure water ________ (will / will not) normally conduct electricity.

Answer 73

) Molecules, will not.

Question 74

To carry out the so-called “electrolysis of water”, sulphuric acid is added to water. How does the addition of sulphuric acid produce a conducting solution.

Answer 74

Sulphuric acid ionizes to form ions.

Question 75

Question .17. (i) State what is observed when copper sulphate solution is electrolyzed using a platinum anode.

Answer 75

Blue colour of the solution disappears.

Question 76

What ions must be present in a solution used for electroplating a particular metal.

Answer 76

Metal ions of the metal with which electroplating is done.

Question 77

A solution of silver nitrate is a good electrolyte but it is not used for electroplating an article with silver.

Answer 77

) Because electroplating is not uniform due to very fast reaction.