Question 1

Question 2Differentiate between(i) Electrolytes and Non-electrolytes(ii) Strong and Weak electrolytes(iii) Anode and Cathode(iv) Electrolytic dissociation and ionization with suitable examples.

Accepted Answer

(i) Differences between Electrolytes and Non-electrolytes are:ElectrolytesNon-electrolytesChemical compound which conduct electricity in the fused or in aqueous solution state and undergo chemical decomposition due to the flow of current through it.Chemical compound which do not conduct electricity in the fused or aqueous solution state and do not undergo chemical decomposition due to the flow of current through it.Electrolytes are ionic compoundsNon-electrolytes are covalent compoundsParticles in Electrolytes – ions only or Ions and molecules onlyParticles in non-electrolytes – Molecules onlyExamples :Acids — dil. HCl, HNO3 H2SO4.Alkalis — KOH, NaOH solutions.Ionic salts — PbBr2 [molten], CuSO4 [aq.]Examples :Pure or distilled water, Alcohol, Kerosene, Carbon disulphide, liquid carbon tetrachloride, sucrose, glucose, sugar solution.(ii) Differences between Strong and Weak electrolytes are:Strong electrolytesWeak electrolytesThey are electrolytes which allow a large amount of electricity to flow through them and hence are good conductors of electricity.They are electrolytes which allow small amount of electricity to flow through them and hence are poor conductors of electricity.They are almost completely dissociated in fused or aqueous solution state.They are partially dissociated in fused or aqueous soln. state.Particles in strong electrolytes are mainly ions onlyParticles in weak electrolytes are ions and unionized molecules.Examples :Generally all strong acids and bases and most salts of strong acids.Acids: dil. HCl, H2SO4, HNO3, HBr, HI.Bases : NaOH, KOH, LiOH soln.Salts: NaCl, NaNO3, Na2SO4, CuCl2Examples :Generally all weak acids and bases and most salts of weak acids.Acids: Carbonic, Acetic, Oxalic, Formic.Bases: NH4OH, Ca(OH)2, Mg(OH)2.Salts: Sodium carbonate, bicarbonate, oxalate and formate aq. soln.(iii) Differences between Anode and Cathode are:AnodeCathodeIt is the electrode connected to the positive terminal of the batteryIt is the electrode connected to the negative terminal of the battery.Anions migrate to anodeCations migrate to cathode.The anions donate excess electrons to the anode and they are oxidised to neutral atoms. Hence, Anode is the Oxidising Electrode.The cations gain excess electrons from the cathode and they are reduced to neutral atoms. Hence, Cathode is the Reducing Electrode.(iv) Differences between Electrolytic dissociation and ionization are:Electrolytic DissociationIonizationIt is a process which takes place in electrovalent compoundsIt is a process which takes place in covalent compounds.It involves separation of ions which are already present in an ionic compounds.It involves formation of charged ions from molecules which are not in the ionic state.PbBr2 (ionic) ⇌ Pb2+ + 2Br1-HCl [aq.] (covalent) ⇌ H1+ + Cl1-.Ionization may also involve atoms changing into ions [e.g. Mg ⟶ Mg2+ + 2e-]

Question 2

Question 12State the reason for difference in product formed at the anode during electrolysis of aq. CuSO4 using :(i) active electrode — copper anode(ii) inert electrode — platinum anode.

Accepted Answer

(i) Electrolysis of aq. CuSO4 using copper anode — Product at anode is nil. [Copper ions are formed]Reaction at anode: Cu - 2e- ⟶ Cu2+SO42- and OH- ions migrate to anode but neither of them are discharged due to the nature of anode, (copper loses electrons more easily than SO42- and OH-) because copper anode itself ionises to give Cu2+ ions.(ii) Electrolysis of aq. CuSO4 using inert platinum anode — Product at anode is oxygen gas.SO42- and OH- ions migrate to anode but OH- ions are discharged since they are lower in the electrochemical series.Oxidation of the OH- ions gives unstable hydroxyl radical which forms water with the liberation of oxygen.

Question 3

Question 15Give reasons for the following changes —(i) pure water a non-electrolyte — becomes an electrolyte on addition of dil. H2SO4(ii) Blue colour of aq. CuSO4 — turns almost colourless on it's electrolysis using Pt electrodes.

Accepted Answer

(i) Pure water is almost a non-electrolyte and will not normally conduct electricity. It consists almost entirely of molecules. It can be electrolytically decomposed by addition of traces of dil. H2SO4 which dissociates as: H+1 and SO42- and help in dissociating water into H+1 and OH- ions, water being a polar solvent. Hence, pure water a non-electrolyte, becomes an electrolyte on addition of dil. H2SO4(ii) The blue colour of CuSO4 solution is due to the Cu2+ ions. During it's electrolysis using Pt electrodes, at the cathode Cu2+ ions are discharged as neutral copper atoms by accepting electrons. These are not replaced by Cu2+ ions from the Anode because at the Anode, OH- ions are discharged. Hence, the blue colour of CuSO4 solution fades and it becomes almost colourless on it's electrolysis using Pt electrodes.

Question 4

Question 16'Iron is electroplated with silver' —(i) define the term in italics(ii) state two reasons for electroplating(ii) state why the iron is not placed at the anode and silver at the cathode during electroplating.

Accepted Answer

(i) Electroplating — It is the electrolytic process of deposition of a superior metal [i.e., nickle, silver, chromium, gold] on the surface of a baser metal or article [e.g., iron, copper, brass](ii) Reasons for electroplating:Prevents corrosion or rusting — of the base metal.Makes the article attractive and gives it an expensive appearance.(iii) The article to be electroplated (i.e., iron) is always placed at the cathode because during electrolytic reaction the metal is always deposited at the cathode by gain of electrons.The metal to be plated on the article (i.e., silver) is always made the anode because the metal anode continuously dissolves as ions in solution and is hence replaced periodically.

Question 5

Question 17Draw a diagram for —(i) electroplating an article with silver;(ii) electrorefining or purification of copper.

Accepted Answer

(i) Below diagram shows electroplating an article with silver:(ii) Below diagram shows electrorefining or purification of copper:

Question 6

Question 18State the (i) electrolyte (ii) cathode used (iii) anode used (iv) electrode reaction at cathode (v) electrode reaction at anode (vi) product at cathode and anodeduring(a) electroplating an article with nickel (b) electroplating a spoon with silver (c) purification of impure copper.

Accepted Answer

(a) Electroplating an article with nickel :Electrolyte — Aqueous solution of Nickle SulphateCathode used — Cleaned article to be electroplatedAnode used — Active electrode. Plate or block of nickle metalElectrode reaction at cathode — Ni2+ + 2e- ⟶ Ni [deposited]Electrode reaction at anode — Ni - 2e- ⟶ Ni2+Product at cathode — Nickel. (It is deposited on the article.)Product at anode — Nil (Ni2+ ions formed)(b) Electroplating a spoon with silver :Electrolyte — Sodium argentocyanide Na[Ag(CN)2]Cathode used — Cleaned article to be electroplatedAnode used — Active electrode. Plate or block of Silver metalElectrode reaction at cathode — Ag1+ + 1e- ⟶ Ag [deposited]Electrode reaction at anode — Ag - 1e- ⟶ Ag1+Product at cathode — Silver. (It is deposited on the article.)Product at anode — Nil (Ag1+ ions formed)(c) Purification of impure copper :Electrolyte — Aqueous copper sulphate solution [acidified]Cathode used — Pure thin sheet of copperAnode used — Impure block of copperElectrode reaction at cathode — Cu2+ + 2e- ⟶ Cu [deposited]Electrode reaction at anode — Cu - 2e- ⟶ Cu2+ [cation]Product at cathode — Pure Copper. (It is deposited over thin sheet of pure Copper.)Product at anode — Nil (Cu2+ ions formed)

Question 7

Question 21State how activity series of metals plays a role in extraction of metals from oxides.

Accepted Answer

Depending on the ease with which the metals lose their electrons and form ions they are arranged in metal activity series or electrochemical series.The arrangement is so done that the elements that ionize most readily [discharged with great difficulty] are placed at the top of the series and other elements in the descending order.Metals at the top of the series (eg. K, Na, Ca, Mg, Al) ionize most readily. Being highly reactive, they cannot be reduced by common reducing agent like C, CO, H2.Metals at the middle of the activity series (eg. Zn, Fe, Pb, Cu), being less reactive, can be extracted from their ores by reduction with common reducing agents like C, CO, H2.Metals near the bottom of the activity series (eg. Hg, Ag), due to their very low reactivity, can be extracted from their ores, by heating only.Metal at the bottom of the activity series (Au, Pt) exist in native state .

Question 8

Question 11. ElectrolysisComplete and balance the electrode reactionsa. Electrolysis of fused lead bromide   1. Dissociation of lead bromidePbBr2 ⇌ ............... + ............... [ions present Pb2+, Br1-] ]2. Reaction at cathode [inert-graphite]Pb2+ + ............... ⟶ ............... [product Lead metal]3. Reaction at anode [inert-graphite]Br1- - ............... ⟶ ...............Br + Br ⟶ ............... [product Bromine vapours]b. Electrolysis of acidified water   4. Dissociation of acidified waterH2SO4 ⇌ ............... + ...............   H2O ⇌ ............... + ............... [ions H1+, SO42-, OH1-]5. Reaction at cathode [inert-platinum]H1+ + ............... ⟶ ...............   H + H ⟶ ............... [product Hydrogen gas]6. Reaction at anode [inert-platinum]OH1- - ............... ⟶ ...............   4OH ⟶ ............... + ............... [product oxygen gas]c. Electrolysis of aq. copper sulphate [Active-copper electrode] 7. Dissociation of aq. copper sulphateCuSO4 ⇌ ............... + ............... [ions present — Cu2+, H1+, SO42-, OH1-]H2O ⇌ ............... + ...............8. Reaction at cathode [copper (or Pt. or C)]Cu2+ + ............... ⟶ ............... [product copper metal]9. Reaction at anode [active copper]Cu - ............... ⟶ ............... [product nil - Cu2+ ions][Inert-platinum electrode]Dissociation of aq. copper sulphateCuSO4 ⇌ ............... + ............... [ions present — Cu2+, H1+, SO42-, OH1-]H2O ⇌ ............... + ...............Reaction at cathode [Pt. or Carbon or Cu]Cu2+ + ............... ⟶ ............... [product copper metal]Reaction at anode [inert-Pt. or C]OH1- - ............... ⟶ ...............4OH ⟶ ............... + ............... [product oxygen gas]

Accepted Answer

1. ElectrolysisComplete and balance the electrode reactionsa. Electrolysis of fused lead bromide   1. Dissociation of lead bromidePbBr2 ⇌ Pb2+ + 2Br1- [ions present Pb2+, Br1-] ]2. Reaction at cathode [inert-graphite]Pb2+ + 2e- ⟶ Pb [product lead metal]3. Reaction at anode [inert-graphite]Br1- - 1e- ⟶ BrBr + Br ⟶ Br2 [product Bromine vapours]b. Electrolysis of acidified water   4. Dissociation of acidified waterH2SO4 ⇌ 2H1+ + SO42-   H2O ⇌ H1+ + OH1- [ions H1+, SO42-, OH1-]5. Reaction at cathode [inert-platinum]H1+ + 1e- ⟶ H x 4   2H + 2H ⟶ 2H2 [product Hydrogen gas]6. Reaction at anode [inert-platinum]OH1- - 1e- ⟶ OH x 4   4OH ⟶ 2H2O + O2 [product oxygen gas]c. Electrolysis of aq. copper sulphate [Active-copper electrode]7. Dissociation of aq. copper sulphateCuSO4 ⇌ Cu2+ + SO42- [ions present — Cu2+, H1+, SO42-, OH1-]H2O ⇌ H1+ + OH1-8. Reaction at cathode [copper (or Pt. or C)]Cu2+ + 2e- ⟶ Cu [product copper metal]9. Reaction at anode [active copper]Cu - 2e- ⟶ Cu2+ [product nil - Cu2+ ions][Inert-platinum electrode]Dissociation of aq. copper sulphateCuSO4 ⇌ Cu2+ + SO42- [ions present — Cu2+, H1+, SO42-, OH1-]H2O ⇌ H1+ + OH1-Reaction at cathode [Pt. or C or Cu)]Cu2+ + 2e- ⟶ Cu [product copper metal]Reaction at anode [inert-pt. or C]OH1- - 1e- ⟶ OH x 44OH ⟶ 2H2O + O2 [product oxygen gas]

Question 9

Question 2B2. B Electrorefining of copperComplete and balance the electrode reactions16. Dissociation of aq. copper sulphateCuSO4 ⇌ ............... + ...............   H2O ⇌ ............... + ...............17. Reaction at cathode [pure thin sheet of Cu]Cu2+ + ............... ⟶ ............... [Cu deposited on thin sheet]18. Reaction at anode [impure block of active Cu]Cu - ............... ⟶ ............... [product nil - Cu2+ ions]Electrometallurgy of sodium   19. Dissociation of sodium chloride fusedNaCl ⇌ ............... + ...............20. Reaction at cathode [inert - electrode]Na1+ + ............... ⟶ ............... [product Na metal]21. Reaction at anode [inert - electrode]Cl1- - ............... ⟶ ...............   Cl + Cl ⟶ ............... [product Cl2 gas]Electrometallurgy of aluminium   22. Dissociation of pure aluminaAl2O3 ⇌ ............... + ...............23. Reaction at cathode [inert - electrode]Al3+ + ............... ⟶ ............... [product Al metal]24. Reaction at anode [inert - electrode]O2- - ............... ⟶ ............... ⟶ 3O2 [product O2 gas]

Accepted Answer

2. B Electrorefining of copperComplete and balance the electrode reactions16. Dissociation of aq. copper sulphateCuSO4 ⇌ Cu2+ + SO42-   H2O ⇌ H1+ + OH1-17. Reaction at cathode [pure thin sheet of Cu]Cu2+ + 2e- ⟶ Cu [Cu deposited on thin sheet]18. Reaction at anode [impure block of active Cu]Cu - 2e- ⟶ Cu2+ [product nil - Cu2+ ions]Electrometallurgy of sodium   19. Dissociation of sodium chloride fusedNaCl ⇌ Na1+ + Cl1-20. Reaction at cathode [inert - electrode]Na1+ + 1e- ⟶ Na [product Na metal]21. Reaction at anode [inert - electrode]Cl1- - 1e- ⟶ Cl   Cl + Cl ⟶ Cl2 [product Cl2 gas]Electrometallurgy of aluminium   22. Dissociation of pure aluminaAl2O3 ⇌ 2Al3+ + 3O2-23. Reaction at cathode [inert - electrode]2Al3+ + 6e- ⟶ 2Al [product AL metal]24. Reaction at anode [inert - electrode]3O2- - 6e- ⟶ 3[O] ⟶ 3O2 [product O2 gas]

Question 10

Question 5(a)Copy and complete the following table which refers to two practical applications of electrolysis.  AnodeElectrolyteCathode(i) Silver plating of a spoon  Solution of potassium argentocyanide  (ii) Purification of copper      (iii) Extraction of copper

Accepted Answer

AnodeElectrolyteCathode(i) Silver plating of a spoonblock of pure silverSolution of potassium argentocyanidespoon to be electroplated(ii) Purification of copperImpure block of copperA solution of copper sulphate and dil. sulphuric acid.Thin strip of pure copper(iii) Extraction of sodiumGraphitefused sodium chlorideIron

Question 11

Question 20Assertion (A): Weak electrolytes do not allow any electricity to flow through them.Reason (R): Substances which are composed of only molecules do not allow any current to flow through them.Both A and R are true and R is the correct explanation of A.Both A and R are true but R is not the correct explanation of A.A is true but R is false.A is false but R is true.

Accepted Answer

A is false but R is true.Explanation — Electrolytes which allow small amounts of electricity to flow through them are called weak electrolytes. These are poor conductors of electricity. Hence the assertion (A) is false.Substances which are composed of only molecules are non electrolytes, they do not allow any current to flow through them. For example, Benzene, glucose.Hence the reason (R) is true.

Question 12

Question 22Assertion (A): An electrolyte can be acid, base or salt.Reason (R): An electrolyte is a substance which can conduct electricity in aqueous or molten state.Both A and R are true and R is the correct explanation of A.Both A and R are true but R is not the correct explanation of A.A is true but R is false.A is false but R is true.

Accepted Answer

Both A and R are true but R is not the correct explanation of A.Explanation — Electrolytes include acids (like HCl), bases (like NaOH), and salts (like NaCl). Hence, assertion (A) is true.Electrolytes conduct electricity in aqueous or molten states because they produce ions. Hence, Reason (R) is true.The reason correctly describes what an electrolyte does, but it doesn’t directly explain why acids, bases, and salts are classified as electrolytes. Hence, both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).

Question 13

Question 23Assertion (A): Oxidation occurs at the anode.Reason (R): Electrons are gained at the anode.Both A and R are true and R is the correct explanation of A.Both A and R are true but R is not the correct explanation of A.A is true but R is false.A is false but R is true.

Accepted Answer

A is true but R is false.Explanation — The reaction at anode involves oxidation of anions as they lose electrons to become neutral. Hence the assertion (A) is true.Electrons are donated or lost at the anode. However, gain of electrons takes place at cathode, where cations are reduced. Hence the reason (R) is false.

Question 14

Question 24Assertion (A): Polar covalent compounds can form ions when dissolved in water.Reason (R): Electrovalent compounds show dissociation.Both A and R are true and R is the correct explanation of A.Both A and R are true but R is not the correct explanation of A.A is true but R is false.A is false but R is true.

Accepted Answer

Both A and R are true but R is not the correct explanation of A.Explanation — Polar covalent compounds are converted into ions in water , and these ions conduct electricity. Hence assertion (A) is true.For example : water.Electrovalent compounds when melted or dissolved in water, electrostatic force of attraction is broken and they dissociate into ions and conduct electricity.Hence the reason (R) is true.Since reason (R) doesn't explain the ionisation of polar covalent compound it is not correct explaination of assertion (A).

Question 15

Question 25Assertion (A): A block of pure silver metal is used as anode during silver plating.Reason (R): Silver ions are deposited as metal at the anode.Both A and R are true and R is the correct explanation of A.Both A and R are true but R is not the correct explanation of A.A is true but R is false.A is false but R is true.

Accepted Answer

A is true but R is false.Explanation — The block of pure silver is used as anode because it is active electrode, as it slowly dissolves in the solution, Ag⁺ ions are produced for the plating process. Hence the assertion (A) is true.Silver ions are deposited on to the article that acts as cathode. Hence reason (R) is false.

Question 16

Question 1(f)Give reasons for the following:Ammonia is unionized in the gaseous state but in the aqueous solution, it is a weak electrolyte.

Accepted Answer

NH3 is polar covalent in nature, i.e., shows charge distribution in its molecules such that the 3 hydrogen atoms have a slight positive charge and Nitrogen atom has a slight negative charge.The nitrogen atom in ammonia has a lone pair of electrons. In aqueous solution, the ammonia molecule combines with a hydrogen atom H+ by sharing the lone pair of electrons of nitrogen atom to form ammonium ion (NH4+). Thus, in water, ammonium hydroxide (NH4OH) dissociates into NH4+ (ammonium ion) and OH- (hydroxide ion) as follows:NH4OH ⟶ NH4+ + OH-Due to this ionization, aqueous solution of ammonia (NH4OH) behaves as a weak electrolyte.

Question 17

Question 2Explain :(a) Sodium Chloride will conduct electricity only in fused or aq. soln. state.(b) In the electroplating of an article with silver, the electrolyte sodium argento-cyanide solution is preferred over silver nitrate solution.(c) Although copper is a good conductor of electricity, it is a non-electrolyte.

Accepted Answer

(a) The ions Na+ and Cl- are not free but held together by strong electrostatic force of attraction. In fused or molten state the ions break free and move. Hence, NaCl will conduct electricity only in fused state or aq. soln. state.(b) Migration of Ag1+ ions from sodium argento-cyanide solution is slow compared to that from silver nitrate. Hence, an even deposition of metal silver is obtained on the article. Therefore, the electrolyte sodium argento-cyanide solution is preferred over silver nitrate solution.(c) Copper does not undergo chemical decomposition due to flow of electric current through it. Hence, copper is a good conductor of electricity but it is a non-electrolyte.

Question 18

Question 3(b)What is the difference between Electrolytic dissociation and ionisation

Accepted Answer

Electrolytic dissociationIonisationSeparation of ions which are already present in an ionic compoundFormation of positively or negatively charged ions from molecules which are not initially in the ionic state.Electrovalent compounds show dissociation e.g., potassium chloride, lead bromide, etc.Polar covalent compounds show ionisation e.g., HCl, NH4OH etc.,KCl ⟶ K+ + Cl-HCl→H2OH++Cl−	ext{HCl} \xrightarrow{	ext{H}_2	ext{O}} 	ext{H}^{+} + 	ext{Cl}^{-}HClH2​O​H++Cl−

Question 19

Question 3(e)What is the difference between Strong electrolyte and weak electrolyte

Accepted Answer

Strong electrolyteWeak electrolyteStrong Electrolyte allow a large amount of electricity to flow through them.Weak electrolytes allow small amount of electricity to flow through them.These are good conductors of electricity.These are poor conductors of electricity.These are almost, completely dissociated in fused or aqueous solution state.These are partially dissociated in fused or aqueous solution state.These solutions contain (almost) only free mobile ions.These solutions contain ions as well as molecules.Strong electrolyte allows a bulb to glow brightly.Weak electrolyte allows a bulb to glow dimly.Examples:Acids — Hydrogen chloride, Nitric acid, etc.Bases — NaOH, KOH (aqueous or molten state)Salts — NaCl (molten or aqueous), PbBr2 (molten), CuCl2 (aq.), CuSO4 (aq.)Examples:Acids — Carbonic acid, acetic acid, oxalic acid etc.Bases — Ammonium hydroxide, calcium hydroxide (aqueous or molten state)Salts — Ammonium carbonate, lead acetate

Question 20

Question 8To 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 ?

Accepted Answer

Water in pure state consists almost entirely of molecules. Hence it is a non-electrolyte that will not conduct electricity.Water is a polar covalent compound. It can be electrolytically decomposed by addition of traces of dil. H2SO4 which dissociates as: H+1 and SO42- and help in dissociating water into H+1 and OH- ions. Thus, dilute sulphuric acid catalyses the ionisation of water to produce a conducting solution.

Electrolysis

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