Students of ICSE Class 10 should refer to Electrolysis ICSE Class 10 Chemistry board year questions and solutions. below which have come in past board exams. You should always go through questions that have come in previous years. This will help you to understand the pattern of questions in ICSE Class 10 Chemistry and prepare accordingly. This will help you to get better marks in ICSE Class 10 Board Exams
ICSE Class 10 Chemistry Electrolysis Board Exam Questions
Students should learn the important questions and answers given below for Chapter Electrolysis in Chemistry for ICSE Class 10. These board questions are expected to come in the upcoming exams. Students of ICSE Class 10th should go through the below board exams questions and answers which will help them to get more marks in exams.
Board Exam Questions Electrolysis ICSE Class 10 Chemistry
(a) Molten lead bromide conducts electricity. It is called an (1) ……….. It is composed of lead ions and bromide (2) ……… . The lead (3) ………are (4) ………charged and are called (5) ………… . The bromide (6) ………are (7) ……….charged and are called (8) ……… . During electrolysis, the lead (9) ………..are attracted to the (10) ………….charged electrode which is called (11) …………and the bromide. (12) ………….are attracted towards the (13) ………….. charged electrode which is called (14) ………… .
Answer
(1) electrolyte (2) ions (3) ions (4) positively
(5) cations (6) ions (7) negatively (8) anions
(9) ions (10) negatively (11) cathode (12) ions
(13) positively (14) anode
(b) Solid lead (II) bromide will not conduct an (1) ………………….The (2) ……….are held in a rigid crystal (3) …………and are not free to move to the (4) ………… . When the solid is (5) ……………., it (6) …………..and allows the passage of an electric current (7) ………….is liberated at the cathode and (8) ……………..at the anode. The decomposition of an electrolyte by an electric current is called (9) …………….
Answer
(1) Electric current (2) ions (3) lattice (4) electrodes
(5) heated (6) melts (7) lead (8) bromine
(9) electrolysis
(c) For electroplating an article with nickel require an (1) ……… which must be a solution containing (2) ……… ions. The article to be plated is placed as the (3) ……… of the cell on which the plating is carried out. The (4) ……… of the cell is made from pure nickel. The ions which are attracted to the negative electrode and discharged are called (5) ……… .
Answer
(1) electrolyte (2) nickel (3) cathode (4) anode
(5) cations
(d) 1. Electrolysis is the passage of …………………. through a liquid or a solution accompanied by a …………………. change.
Answer
electricity, chemical
2. An electrically charged atom is called……….. .
Answer
an ion
3. The solution of a substance which conducts electricity is called ………………… .
Answer
an electrolyte
4. An electrolyte is a……………… .
Answer
good conductor of electricity
5. A weak electrolyte is one which………………… .
Answer
is feebly ionized in the solution
6. A strong electrolyte is one which…………………. .
Answer
is completely ionized in the solution
7. Sodium chloride is……………. .
Answer
strong electrolyte
8. Water is…………………… .
Answer
a weak electrolyte
9. The electrode where the current enters the electrolyte is called the………..
Answer
anode
10. Negative electrode is called the………. .
Answer
cathode
11. Cations migrate to…………during electrolysis.
Answer
cathode
12. During electrolysis, anions undergo……………………at the………………
Answer
oxidation, anode
13. The reactions occurring at the cathode during electrolysis involve……………………
Answer
reduction
14. ………… is a non-electrolyte.
Answer
sugar
15. Pure water consists almost entirely of ……………
Answer
molecules
16. We can expect that pure water………normally conduct electricity.
Answer
will not
17. Elements liberated at the anode during electrolysis are said to be………………
Answer
electronegative
18. In solution or in molten state a ……………… electrolyte consists almost entirely of ions.
Answer
strong
19. As we descend the electrochemical series containing cations, the tendency of the cations to get …………………….. at the cathode increases.
Answer
reduced
20. The……………….. the concentration of an ion in a solution, the greater is the probability of its being discharged at its appropriate electrode.
Answer
higher
21. In the electrolysis of acidulated water, oxygen is produced by the discharge of…………… ions at the anode.
Answer
OH–
22. ………… lead bromide does not conduct electricity.
Answer
solid
23. Ionization is a ……………… process.
Answer
reversible
24. Hydrogen chloride ………………when dissolved in water.
Answer
ionizes
25. A solution of hydrogen chloride gas in water conducts electricity because………………. but a solution of hydrogen chloride gas in toluene does not conduct an electric current because………………………….. .
Answer
it ionizes in solution to form free ions; it remains as a single molecule in solution.
26. The gas given off at cathode during the electrolysis of acidulated water is……………. .
Answer
hydrogen
27. With platinum electrodes, hydrogen is liberated at the ………… and oxygen at the ………… during the electrolysis of acidified water.
Answer
cathode, anode
MCQ on Electrolysis Class 10 Chemistry Questions with Answers
Check Our MCQ on Electrolysis Class 10 with Answers free Pdf download. Class 10 Chemistry MCQ Questions with Answers are prepared according to the latest exam pattern of Icse boards. We have Provided you Electrolysis Class 10 ICSE MCQ Questions with Answers to make your preparation to score good marks in the Class 10 exam.
Question. Identify the weak electrolyte from the following :
(a) Sodium Chloride solution
(b) Dilute Hydrochloric acid
(c) Dilute Sulphuric acid
(d) Aqueous acetic acid
Answer
D
Question. Which of these will act as a non-electrolyte ?
(a) Liquid carbon tetrachloride
(b) Acetic acid
(c) Sodium hydroxide aqueous solution
(d) Potassium chloride aqueous solution
Answer
A
Question. During ionisation metals lose electrons, this change can be called :
(a) Oxidation
(b) Reduction
(c) Redox
(d) Displacement
Answer
A
Question. The metallic electrode which does not take part in an electrolytic reaction.
(a) Cu
(b) Ag
(c) Pt
(d) Ni
Answer
C
Question. When dilute sodium chloride is electrolysed using graphite electrodes, the cation is discharged at the cathode most readily.
(a) Na+
(b) OH–
(c) H+
(d) Cl–
Answer
C
Question. During electrolysis of NaCl, the gas released at anode is :
(a) Chlorine
(b) Oxygen
(c) Hydrogen
(d) None of the above
Answer
B
Question. 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
D
Question. A compound which liberates reddish brown gas around the anode during electrolysis in its molten state is :
(a) Sodium chloride
(b) Copper (II) oxide
(c) Copper (II) sulphate
(d) Lead (II) bromide
Answer
D
Question. When fused lead bromide is electrolysed we observe :
(a) a silver grey deposit at anode and a reddish brown deposit at cathode
(b) a silver grey deposit at cathode and a reddish brown deposit at anode
(c) a silver grey deposit at cathode and reddish brown fumes at anode
(d) silver grey fumes at anode and reddish brown fumes at cathode.
Answer
C
Question. The vessel in which electrolysis of Lead bromide is carried out is :
(a) Clay crucible
(b) Glass vessel
(c) Silica crucible
(d) Aluminium vessel
Answer
C
Question. The ion which is discharged at the cathode during the electrolysis of copper sulphate solutions using copper electrodes as anode and cathode.
(a) Cu2+
(b) OH–
(c) SO42–
(d) H+
Answer
A
Question. An aqueous electrolyte consists of the ions mentioned in the list, the ion which could be discharged most readily during electrolysis.
(a) Fe2+
(b) Cu2+
(c) Pb2+
(d) H+
Answer
B
Question. During silver plating of an article using potassium argentocyanide as an electrolyte, the anode material should be :
(a) Cu
(b) Ag
(c) Pt
(d) Fe
Answer
B
Question. The particles present in strong electrolytes are :
(a) only molecules
(b) mainly ions
(c) ions and molecules
(d) only atoms
Answer
B
Electrolysis Class 10 ICSE MCQ Questions are given here. You can easily download MCQ on Electrolysis Class 10 free of charge to score well in the exam. These books cover the whole ICSE syllabus as recommended by the Council. Preparing from these books will help in making concepts. Students can utilize this Electrolysis Class 10 MCQ for their board exams. Besides, this MCQ are great study material to prepare for competitive exams.
We hope the given MCQ on Electrolysis Class 10 Chemistry with Answers Pdf free download will help you. If you have any issue in regard to MCQ Questions for Class 10 ICSE Chemistry Electrolysis. Drop a comment below and we will guide you as soon as possible.
Give One Word/Chemical Term
Question. The fundamental particles of the atoms that move when electric current is passed through a metal wire.
Answer
Electron
Question. The type of substances which undergo decomposition in aqueous solution form when electric current passes through them.
Answer
Strong electrolytes
Question. The type of materials which neither in solution nor in molten state allows an electric current to pass through it.
Answer
Non-electrolytes
Question. The process by which a particle gains or loses electrons.
Answer
Ionization
Question. The process by which an electrovalent substance breaks up into free mobile ions in the molten or aqueous form.
Answer
Dissociation
Question. An acid which is added during electrolysis of water.
Answer
Conc. H2SO4
Question. The acid used in electrolysis of water.
Answer
Sulphuric acid
Question. Electrodes used in electrolysis of copper sulphate.
Answer
Platinum electrodes
Question. A material used for making attackable electrodes.
Answer
Platinum
Question. Liquid which does not conduct electricity.
Answer
Non-electrolyte
Question. Electrolytic deposition of a superior metal on a baser metal.
Answer
Electroplating
Question. Electrolyte used in the process of silver plating.
Answer
Potassium argento cyanide
Question. Electrolyte used in the process of nickel plating.
Answer
Nickel ammonium sulphate
Question. A suitable cathode used in the electrorefining of copper.
Answer
Sheets of pure copper metal
Question. Impurities which remain behind at the bottom of the cell.
Answer
Anode mud
Question. Process used for obtaining highly electropositive metals.
Answer
Electrometallurgy
Define/Explain the Following
1. Electrolysis
Ans. The process due to which, a chemical compound in aqueous or fused state conducts direct electric current and at the same time undergoes chemical decomposition, due to the discharge of charged ions is called electrolysis.
2. Electrolytes.
Ans. An electrolyte is a substance, which in the fused state or in aqueous solution conducts an electric current and itself is decomposed as a result of electric current passing through it. For example sodium chloride, potassium chloride and acidulated water.
3. Strong electrolyte
Ans. An electrolyte having high degree of dissociation, is termed as strong electrolyte and hence it is completely dissociated in solution.
4. Weak electrolytes
Ans. The compounds which in their fused state or aqueous solution are feebly ionised and are poor conductors of electricity are called weak electrolytes. For example, acetic acid, oxalic acid.
5. Non-electrolytes
Ans. Non-electrolytes are substances which do not allow the current to pass through them either in the molten state or in aqueous solution. Non electrolytes are non-ionic.
6. Electrolytic cell
Ans. The vessel in which electrolysis is carried out consisting of two electrodes and an electrolyte is called an electrolytic cell or voltameter.
7. Electrodes
Ans. The graphite or metal plates or rods, through which current enters or leaves an electrolyte, are called electrodes.
8. Cathode
Ans. The electrode which is connected to the negative terminal of a battery, or a cell, is called cathode. The current from electrolyte leaves through cathode.
9. Anode
Ans. The electrode which is connected to the positive terminal of a battery, or a cell, is called anode. The current enters the electrolyte from anode.
10. Ions
Ans. When a chemical compound in fused state or in aqueous solution, breaks up into electrically charged atoms or group of atoms, then they are collectively called ions. For example, K+, Mg2+, Ca2+, F–, I–, S2–
11. Cations
Ans. The positively charged ions, which migrate towards cathode on the passage of electric current, are called cations. The cations accept electrons from cathode and change to neutral atoms. For example, Na+, Ca2+, K+.
12. Anions
Ans. The negatively charged ions, which migrate towards anode on the passage of electric current are called anions. The anions donate electrons to anode and change to neutral atoms. For example, Cl–, I–, OH–.
13. Ionisation
Ans. The process of formation of positively and negatively charged ions from molecules which are not initially in the ionic state is called ionisation. e.g., Polar covalent compound HCl.
HCl → H+ + Cl–
14. Dissociation
Ans.The process of separation of ions which are already present in an ionic compound is called electric dissociation. e.g., electrovalent compounds, NaCl.
NaCl → Na+ + Cl–
15. Reduction
Ans. A process of gaining of electrons by a cation to form neutral atom (or gaining of electrons by an electronegative atom to form an anion) is called reduction. Reduction takes place at cathode.
16. Oxidation
Ans. A process of loss of electrons by an atom to form a cation (or loss of electrons by an anion to form atom) is called oxidation. Oxidation takes place at anode.
17. Ionic equation
Ans. A chemical equation which represents the actual atoms (unionised) or ions or radicals taking part in a chemical reaction by the actual exchange of electrons is called an ionic equation.
18. Electroplating
Ans. The process of depositing a metal, generally a superior metal like silver, gold, chromium or nickel over another metal or article with the help of electric current is called electroplating.
19. Electrometallurgy
Ans. The process of extracting metals from their ores with the help of electrolysis is called electrometallurgy. Highly electronegative metals like Na, K, Mg, Ca and Al are extracted by electrolysis of their fused halides or oxides.
Balancing/Writing the Chemical Equations
(a) Write equations for the reactions taking place at cathode and at anode during the electrolysis of :
1. Acidified nickel sulphate solution with nickel electrode.
Answer
Cathode : Ni2+ + 2e– ⎯→ Ni
Anode : Ni – 2e– ⎯→ Ni2+
2. Acidified copper sulphate solution with copper electrode.
Answer
Cathode : Cu2+ + 2e– ⎯→ Cu
Anode : Cu – 2e– ⎯→ Cu2+
3. Acidified copper sulphate solution with platinum electrode.
Answer
Cathode : Cu2+ + 2e– ⎯→ Cu
Anode : OH– – e– ⎯→ OH
4OH– ⎯→ 2H2O + H2
4. Acidulated water with inert electrode.
Answer
Cathode : H+ + e– ⎯→ [H]
2 [H] ⎯→ H2
Anode : OH– – e– ⎯→ OH
4OH ⎯→ 2H2O + O2
5. Molten lead bromide with inert electrodes.
Answer
Cathode : Pb2+ + 2e– ⎯→ Pb
Anode : 2Br– – 2e– ⎯→ 2 [Br]
2[Br] ⎯→ Br2
6. Electroplating a spoon with silver.
Answer
Cathode : AgNO3 ⎯→ Ag+ + NO3–
Ag+ + e– ⎯→ Ag
Anode : NO3– – e– ⎯→ NO3
Ag + NO3 ⎯→ AgNO3
(b) Complete and balance the following equations :
Ans.
(c) Write equations for the reactions taking place at the two electrodes (mentioning clearly the name of the electrode) during the electrolysis of :
1. Acidified copper sulphate solution with copper electrodes.
2. Molten lead bromide with inert electrodes.
Ans.
Reasoning Based Questions
Q. 1. Why are acids, bases and salts classified as electrolytes ?
Answer
Ans. Acids, bases and salts are classified as electrolytes because these compounds dissociate into ions, conduct electricity and undergo chemical decomposition at the same time.
Q. 2. Metals like potassium, calcium, sodium, etc., can be extracted only by electrolysis.
Answer
Ans. Metals like K, Ca, Na, etc., can be extracted only by electrolysis because conventional reducing agents such as coke, carbon monoxide, hydrogen do not supply sufficient energy to break ionic bonds between the active metals and their chlorides or oxides.
Q. 3. Dilute acids are strong electrolytes. Why ?
Answer
Ans. Dilute acids produce a large number of hydronium ions, so they behave like strong electrolytes.
Q. 4. Sea water is a strong electrolyte. Why ?
Answer
Ans. Sea water is a strong electrolyte because sodium chloride dissolved in it dissociates completely into free mobile ions. Na+ Cl– Na+ + Cl–
Q. 5. Copper is a good conductor of electricity, but it is a non-electrolyte. Why ?
Answer
Ans. During metallic conduction, the chemical properties of copper are intact as it does not undergo chemical decomposition. Since, the flow of electricity only produces heat and energy and no new products are formed copper metal is thus a good conductor of electricity but is a nonelectrolyte.
Q. 6. A solution of ionic compound is an electrolyte, while that of covalent compound is nonelectrolyte ?
Answer
Ans. The solution of ionic compound has free ions, which can migrate to cathode and anode and discharge. Thus, solution of ionic compound is good conductor of electricity and hence is an electrolyte. However, a solution of covalent compound, consists of only molecules and does not have any free ions, which could migrate to cathode or anode. Hence, it is a non-electrolyte.
Q. 7. Explain, why hydrochloric acid is a conductor of electricity ?
Answer
Ans. Hydrochloric acid dissociates into ions in aqueous solution as follows : HCl ⇌ H+ + Cl– When a current is passed through in aqueous solution of HCl, the ions move towards their respective electrodes. Thus, the hydrochloric acid is a conductor of electricity.
Q. 8. Does wax conduct electricity ? Give reason to justify your answer.
Answer
Ans. No, wax does not conduct electricity because wax, being a covalent compound, does not have positively or negatively charged ions which could not be weakened by heating or in aqueous solution. Therefore due to absence of free ions, wax does not conduct electricity.
Q. 9. Mercury is a liquid and allows the flow of electricity, though it is not an electrolyte.
Answer
Ans. An electrolyte is a substance which on dissolving in water breaks up into positively and negatively charged ions. But mercury is a metal, so on dissolving in water, it can not break up into cations and anions. When electric current passes through mercury it does not undergo any decomposition and no new substance is formed. Electric current passes through mercury due to the presence of free electrons in its penultimate shell and not due to the formation of ions. Hence, mercury is a metallic conductor and not an electrolyte.
Q. 10. A solution of cane sugar does not conduct electricity, but a solution of sodium chloride is a good conductor.
Answer
Ans. The sugar cane solution is a covalent compound. When it is dissolved in water, it does not dissociate to give free ions which could migrate to cathode or anode. Hence, sugar solution is a bad conductor of electricity. The sodium chloride solution mainly consists of free sodium and chloride ions which could migrate to positively charged electrodes. Hence, solution of sodium chloride is a good conductor of electricity.
Short Questions
Q. 1. Classify following substances under three headings :
Strong electrolytes, Weak electrolytes, Non-electrolytes.
Acetic acid, ammonium chloride, ammonium hydroxide, carbon tetrachloride, dilute hydrochloric acid, sodium acetate, dilute sulphuric acid.
Ans. Strong electrolytes —Ammonium chloride, dilute hydrochloric acid, dilute sulphuric acid.
Weak electrolytes — Ammonium hydroxide, acetic acid, sodium acetates.
Non-electrolyte — Carbon tetra chloride.
Answer
Strong electrolytes —Ammonium chloride, dilute hydrochloric acid, dilute sulphuric acid.
Weak electrolytes — Ammonium hydroxide, acetic acid, sodium acetates.
Non-electrolyte — Carbon tetra chloride.
Q. 2. How will you distinguish between metallic conduction and electrical conduction ?
Answer
Q. 3. Differentiate between an electrolytic cell and electrochemical cell.
Answer
Q. 4. Differentiate between electrical conductivity of copper sulphate solution and copper metal.
Answer
Q. 5. Choose A, B, C or D to match the descriptions (i) to (v) below. Some alphabets may be repeated.
(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 molcules, solute molecules and ions formed by the dissociation of solute molecules.
(v) A sugar solution with sugar molecules and water molecules.
Answer
(i) B
(ii) A
(iii) D
(iv) C (v) A
Q. 6. Give three differences between sodium atom and sodium ion.
Answer
(i) Sodium atom is neutral in nature, while sodium ion is a positively charged particle.
(ii) Sodium atom vigorously reacts with water to liberate hydrogen gas, while sodium ion does not react with water.
(iii) Sodium atom tends to lose an electron to form sodium ion with a complete octet in the outermost shell.
Q. 7. Explain how electrolysis is an example of redox reaction.
Answer
Redox reactions are called simultaneous oxidation-reduction reactions. In electrode reactions, the positively charged ions (cations) accept electrons from cathode to form neutral atoms, i.e., at cathode reduction takes place. At anode, the negatively charged ions (anions) lose electrons to form neutral atoms, i.e., at anode oxidation takes place. So, electrode reactions also signify oxidation-reduction reactions. Hence, they are also called redox reactions.
Q. 8. (i) Write equations to show the electrolytic dissociation of :
Answer
(i) (a) Acids : H2SO4 ⇌ 2H+ + SO42–
HNO3 ⇌ H+ + NO3–
(b) Bases : NaOH ⇌ Na+ + OH–
KOH ⇌ K+ + OH–
(ii) When electricity is passed through fused sodium chloride, the electrolysis starts as follows :
NaCl ⇌ Na+ + Cl–
Na+ → + e– ⎯→ Na (At cathode)
Cl– – e– ⎯→ Cl
Cl + Cl ⎯→ Cl2 (At anode)
Sodium metal is deposited at cathode, while chlorine gas is liberated at anode. Electricity is conducted with the help of free sodium and chloride ions, which are present in fused sodium
chloride.
Q. 9. How is it possible to discharge Na+ ions in preference to H+ ions in electrolysis of NaCl solution ?
Answer
By using cathode made of moving mercury, Na+ ions are discharged in preference to H+ ions because of the nature of electrode. Mercury has strong tendency to form an amalgam with sodium :
Na+ + e– ⎯→ Na
Na + Hg ⎯→ Na/Hg
When the sodium amalgam dissolves in water, the reaction is :
2Na/Hg + 2H2O ⎯→ 2NaOH + H2 + Hg
Q. 10. A certain metal, say M, does not liberate hydrogen from dilute sulphuric acid, but displaces copper from aqueous copper(II) sulphate. State the most likely place for the metal in electrochemical series.
Answer
The activity series is obtained, when we examine replacement of one metal ion from its solution by another metal. The metal (M) which displaces copper from aqueous copper(II) sulphate is placed at higher position as compared to copper in activity series.
Q. 11. M is a metal above hydrogen in the activity series and its oxide has the formula M2O. This oxide when dissolved in water forms the corresponding hydroxide which is a good conductor of electricity. In the above context answer the following :
(i) What kind of combination exists between M and O ?
(ii) How many electrons are there in the outermost shell of M ?
(iii) Name the group to which M belongs.
(iv) State the reaction taking place at the cathode.
(v) Name the product at the anode.
Answer
(i) Electrovalent bond exists between M and O.
(ii) One electron is there in the outermost shell.
(iii) M belongs to First group.
(iv) M+ + e– ⎯→ M (at cathode).
M + M ⎯→ M2
(v) Oxygen gas is liberated at anode.
Q. 12. How will you electrolyse the molten solution of lead bromide ?
Answer
Molten lead bromide (PbBr2) forms Pb2+ and Br– ions. The positive lead ions (Pb2+) move to the cathode, and gain two electrons and change into lead atom.
Pb2+ + 2e– ⎯→ Pb
(Lead)
Lead is deposited at the cathode. The negative bromide ion migrates to the anode. It loses an electron and becomes a bromide atom. The two bromine atoms join bromine molecule. It is
liberated as bromine gas :
Br– – e– ⎯→ Br
Br + Br ⎯→ Br2
Q. 13. (i) What are the particles present in a non-electrolyte ?
(ii) What is conductivity of metals due to ?
(iii) What should be the physical state of lead bromide, if it is to conduct electricity ?
(iv) What particles are present in pure lead bromide ?
Answer
(i) Molecules are present in a non-electrolyte.
(ii) The conductivity of metals is due to movement of electrons.
(iii) Lead bromide should be in molten state, if it is to conduct electricity.
(iv) Lead ions and bromide ions are present in pure lead bromide in molten state.
Q. 14. (i) When the electrolysis of acidified water is carried out :
(a) What is the ratio of the volume of hydrogen produced to the volume of oxygen ?
(b) Give the equation for the discharge of ions at the cathode.
(ii) 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
(i) (a) The ratio is 2 : 1
(b) H+ + e– → H; 2H + 2H ⎯→ 2H2
(ii) Addition of sulphuric acid causes dissociation of water molecules into [H+] and [OH–] ions.
Q. 15. What would happen if in the electrolysis of acidified water, copper electrodes were used instead of platinum ones ?
Answer
At anode : OH– and SO32– would migrate to anode but neither would be discharged, instead copper atoms would get oxidised to Cu2+ and enter solution
Cu ⎯→ Cu2+ + 2e–
The electrolytic solution would become blue in colour. Anode would dissolve.
At cathode : H+ ions would migrate to the cathode and get reduced. Thus, H2 gas would be discharged at cathode
2H+ + 2e– ⎯→ 2H ⎯→ H2
Later, as the solution turns blue due to formation of Cu2+ ions, the Cu2+ ions will get discharged to 2H+ ions as they are less electropositive
Cu2+ + 2e– ⎯→ Cu↓
Q. 16. During the electrolysis of aqueous copper sulphate, between copper electrodes, the sulphate and hydroxyl ions remain as spectator ions.
Answer
During electrolysis of aqueous copper sulphate using copper electrodes, the two anions OH– and SO42– migrate to the anode, but none of them get discharged because the copper of the anode dissolves in the solution producing copper ions and electrons. Hence, OH– and SO42– ions remain as spectator ions.
Q. 17. The following questions refer to the electrolysis of copper sulphate solution with copper electrodes.
(i) Compare the change in mass of the cathode with the change in mass of the anode.
(ii) What happens, when electrolysis of aqueous copper sulphate between platinum electrode, occurs.
(iii) What is the practical application of the electrolysis of copper sulphate solution ? Briefly describe one such application.
Answer
(i) Mass of Cathode increases where as that of anode decreases due to deposition of pure copper on cathode.
(ii) The blue colour of copper sulphate is due to the presence of cupric ions (Cu2+). Cu2+ ions are discharged at the cathode and deposited as Pinkish copper metal, but OH– ions are discharged at anode. The electrolyte consists of hydrogen and sulphate ions which associate to form colourless sulphuric acid.
(iii) The electrolysis of copper sulphate solution is used in the purification of copper using pure copper plate as cathode and impure copper plate as anode.
Q. 18. During the electrolysis of copper(II) sulphate solution using platinum as cathode and carbon as anode :
(i) What do you observe at the cathode and at the anode ?
(ii) What change is noticed in the electrolyte ?
(iii) Write the reactions at the cathode and at the anode.
Answer
(i) At cathode red shiny metal deposits.
At anode bubbles of a colourless odourless gas are seen coming out.
(ii) Colour of electrolyte gradually fades from blue to colourless.
(iii) Reaction at cathode
Cu2+ + 2e– → Cu
Reaction at anode
OH– – e–→ OH
4OH → 2H2O + O2↑
Q. 19. Explain, how the blue colour of electrolyte fades during electrolysis of CuSO4 solution ?
Answer
The blue colour of electrolyte is due to the presence of copper ions in it. As the electrolysis is carried out, the copper ions discharge at the cathode.
Cu2+ + 2e– ⎯→ Cu
However, no copper ions enters in the electrolyte from anode. Thus concentration of copper ions goes on decreasing. This result in fading of blue colour. When copper ions completely finish the electrolyte becomes colourless.
Reaction of cathode :
H+ + 1e– ⎯→ H
H + H ⎯→ H2(g)
Reaction of anode :
OH– – 1e– ⎯→ OH
4OH ⎯→ 2H2O + O2(g)
