Selina Solutions for Class 10 Chemistry ICSE- Electrolysis

Complete Solution of Concise Chemistry Class-X

0
358
Electrolysis
Electrolysis

Get the complete solution of Concise Chemistry for Class-X (Selina) complete free.

Chapter-Electrolysis

Intext Questions

1. Fill in the Blanks.

            a) Powdered sodium chloride does not conduct an electric current, but it does so when melted or when in aqueous solution.

            b) Molten lead bromide conducts electricity. It is called an electrolyte. It is composed of lead ion and bromide ions. The lead ions are positively charged and are called cations. The bromide ions are negatively charged and are called anions.

            c) Substances which conduct electricity in the solid state are generally metallic conductors.

            d) The electron releasing tendency of zinc is more than that of copper.

            e) A solution of HCl gas in water conducts electricity because it furnish ions, but a solution of HCl gas in toluene does not conduct an electric current because it remain in molecular form.

            f) Pure water consists entirely of molecules.

            g) We can expect that pure water will not normally conduct electricity.

            h) Electrolysis is the passage of electricity through a liquid or a solution accompanied by a chemical change.

2. Define the following terms:

      a) Electrolysis: It is the process of breaking down a compound into its ions in molten state or in aqueous solution by passing electric current through it.

      b) Non-electrolyte: Compounds which do not allow electricity to pass through it. Distilled water, CCl4, glucose etc.

      c) Cation: Positively charged ions are called cations. Anion: Negatively charged ions are called anions.

      d) Weak electrolytes: Compounds which dissociated incompletely in aqueous solution or in molten state to produce a less number of ions. Carbonic acid, Acetic acid, ammonium hydroxide, ammonium carbonate, lead acetate, calcium hydroxide etc.

3. What is the difference between:

Modern explanation of ElectrolysisArrhenius explanation of Electrolysis
Electrolytes remain in ionic form even in solid state, held by strong electrostatic forces, water breaks the force and makes the ions mobile.Water ionises electrolytes
Electrolytic dissociationElectrolytic ionization
Separation of ions which are already present in the compound.Formation of ions from molecules which are not initially in ionic state.
CationAnion
Positively charged ionNegatively charged ion
Electrolytic dissociationThermal dissociation
Breaking of a compound by passing electricityBreaking a compound by heating it
Strong electrolyteWeak electrolyte
Compounds which dissociated almost completely in aqueous solution or in molten state to produce a large number of ions.Compounds which dissociated incompletely in aqueous solution or in molten state to produce a less number of ions.

4. Name:

A salt which is a weak electrolyteAmmonium carbonate
A base which is a weak electrolyteCalcium hydroxide
An inert electrode and an active electrodePt and Ag respectively
A positively charged non-metallic ionH+
The electrode at which reduction occursCathode
A non-metallic element which is a conductor of electricityNH4+

5. Electrolysis is a redox process. Explain

During the process of electrolysis, Oxidation occurs at the anode and reduction occurs at the cathode simultaneously.

6. Classify the following substances under three headings:

Strong electrolytesWeak electrolytesNon-electrolytes
Dilute hydrochloric acidAcetic acidCarbon tetrachloride
Sodium acetateAmmonium chloride 
Dilute sulphuric acidAmmonium hydroxide 

7. Explain why:

a) To be an electrolyte, it should be in aqueous or molten state, and should produce something new after passing electricity through it. Cu conducts electricity in solid state due to the electrons present in it and it never produces something new, after the passage of electricity. That’s why Cu is a good conductor but is a non-electrolyte.

b) In solid state, Na+ and Cl ions are held together by strong electrostatic force of attraction, thus in solid state, sodium chloride does not allow electricity to pass through it.

8.

i) Molten ionic compoundB(strong electrolyte)
ii)Carbon tetrachlorideA(non-electrolyte)
iii)An Aluminium wireD(metallic conductor)
iv)A solution containing solvent molecules, solute molecules and ions formed by the dissociation of solute molecules.C(weak electrolyte)
v)A sugar solution with sugar molecules and water moleculesA(non-electrolyte)

Intext Questions

1.Name two substances in each case:

a) Gluose,sucrose,urea,distilled water,or any example of non-electrolyte

b) Sulphuric acid, KOH or example of any strong electrolyte

c) Acetic acid, formic acid or example of any weak electrolyte.

2) Select the ion in each case, that would get selectively discharged from the aqueous mixture of the ions listed below:

a) SO42- , NO3 , OH  → OH ion

b) Pb2+, Ag+ and Cu2+→Ag+

3. a)Cu as metal and Zn2+ as ion.

b)Copper is above silver in the electrochemical series.Thus it can replace silver from silver nitrate solution.

c)Cu is more active.

4. a)Add Cu in silver nitrate solution. Cu+2AgNO3→Cu(NO3)2+2Ag↓

b)Add Zn in Copper sulphate solution.Zn+CuSO4→ZnSO4+Cu↓

5. In both the cases, free ions are formed.

6. During electrolysis of an aqueous solution of sulphuric acid between platinum electrodes, two types of anions migrate towards the anode but only one of them is discharged:

  1. OH and SO42-
  2. Water and oxygen. OH – e→[OH],  4[OH]→2H2O + O2
  3. Hydrogen. H+ + e→H, H + H →H2
  4. As both oxygen and hydrogen are colorless gases.
  5. As the mass of sulphuric acid does not change.

7. a) Electrodes A and B- anode and cathode respectively.

b) Oxidising electrode-A(anode)

8. Sulphuric acid is a strong electrolyte. It helps to increase the conductivity of water.

Exercise-6

1.Give reasons for the following:

a) During electrolysis of molten lead bromide, oxidation takes place at the anode and reduction takes place at the cathode.

Cathode: Pb2+ + 2e → Pb

Anode: Br – e →Br, Br + Br →Br2

b) During electrolysis of copper sulphate solution using platinum electrodes, the number of Cu2+ ions decreases in the electrolyte. As a result, the blue colour of the electrolyte fades out.

c) In solid state, free ions are absent and that’s why solid lead bromide is a non-electrolyte. In molten state, lead bromide produces lead ions and bromide ions.

d) Due to high affinity of oxygen, Aluminium oxide cannot be reduced by conventional reducing agents. Thus, Al is extracted by electrolytic reduction.

e) During electrolysis of water, the number of molecules of hydrogen is twice that of oxygen molecules.

According to Avogadro’s Law, molecules can be substituted by volumes. 2H2O→2H2 + O2. Hence the electrolysis of water gives 2 volumes of hydrogena and 1 volume of oxygen.

f) Sulphuric acid is preferred due to its non-volatile nature. HNO3 cannot be used due to their volatile nature.

g) Ammonia a covalent compound and thus remain unionised in the gaseous state. In aqueous solution, it produces ammonium hydroxide, which furnishes ammonium and hydroxide ion. NH3 + H2O → NH4OH, NH4OH→NH4+ + OH

h) Graphite electrodes are used as it is unaffected by reactive bromine vapour.

i) AgNO3 undergoes fast dissociation causing rough and non-uniform deposit of Ag. Thus AgNO3 is not preferred.

j) Carbon tetrachloride is liquid non polar covalent compound. That’s why it does not conduct electricity.

k) Electrolysis of aqueous solution of potassium salt produces hydrogen at the cathode as hydrogen is below potassium in the electrochemical series.

2. a)

 AnodeElectrolyteCathode
i) Silver plating of a spoonPlate of pure and clean AgSodium argentocyanide solutionArticle to be electroplated
ii) Purification of copperImpure CuCopper sulphate solution with few drops of sulphuric acidPure copper strip
iii)Extraction of sodiumGraphiteMolten NaClIron

 Ag-e →Ag+

Cu – 2e → Cu2+

Cl – e→Cl, Cl+ Cl →Cl2

3. b) CuSO4

    c) Iron object gets deposited by reddish brown copper and the size of the copper rod get reduced.

4.a) X-2e →X2+

       Y+3e → Y3-

   b) X2+ + Y3- → X3Y2

   c) cathode, anode

5. Electroplating , electrorefining

6. a) Molecules

    b) H+, X, HX

    c) loss, gain

    d) Cation of that particular metal

7.AgNO3 solution

2008

a) Anode, Oxidation

b) Cu2+, Cu2+  + 2e → Cu

c) Carbon tetrachloride is a non-polar covalent compound, thus, it is a non-electrolyte.

d) Lead is deposited at the cathode

2009

a) D or CH3COOH

b) Molten lead bromide conducts electricity.

c) i) Complex

    ii) Na[Ag(CN)2] is a complex salt which dissociates slowly causing uniform deposit of Ag. AgNO3 undergoes fast dissociation causing rough and non-uniform deposit of Ag. Thus AgNO3 is not preferred.

    iii) Low DC current for a longer time should be used to have a uniform coating.

    iv) Ag+ + e→ Ag

    v) Ag-e →Ag+

d) i) Ni2+

    ii) Oxygen

2010

a) iv) Lead Bromide

b)

Electrolyte: Nickel sulphate solution

Cathode: Article to be electroplated

Cathode Reaction: Ni2+ + 2e→Ni

Anode: Plate of pure and clean Ni

Anode Reaction: Ni-2e →Ni2+

c) A: NaCl is a strong electrolyte

    B: Acetic Acid is a weak electrolyte

    C: Sugar solution is a non-electrolyte

2011

a) Sulphuric acid initiate the ionisation.

b) i) Reddish Brown Deposit at the cathode

     ii) Blue colour fades

     iii) Cathode: Cu2+  + 2e → Cu, Anode: OH – e → [OH], 4[OH] → 2H2O + O2

c)

Copper Sulphate SolutionCopper Metal
Aqueous  solutionSolid state
IonsFree electrons

2012

a) iv) Aq acetic acid

b) 1→iii, 2→i, 3→ii

c) Furnish ions Na2+, Cl, H+, OH

d) i) Cu2+

    ii) Pt

    iii) OH

    iv) H+

    v) Plate of pure and clean Ag

2013

a) Greyish white metallic deposit at the cathode

b) i) Liquid CCl4

c) i)Left, connected to the positive terminal of the battery.

    ii) Cu – 2e → Cu2+

    iii) Reddish Brown Deposit at the cathode, Blue colour of the electrolyte does not changes.

d) Hydrogen Chloride

2014

a) iii)

b) iii)

c) Electroplating

d) Reddish Brown Deposit

e) Anode, loss of electron takes place

f) i) Na+, H+, OH

    ii) H+, CO32-, OH, H2CO3

    iii) Sugar molecules

g) i) H+  + e → H, H + H →H2

    ii) Oxygen

2015

a) Mass of anode decreases.

b) Graphite electrodes are used as it is unaffected by reactive bromine vapour.

c) During electrolysis of molten lead bromide, oxidation takes place at the anode and reduction takes place at the cathode.

Cathode: Pb2+ + 2e → Pb

Anode: Br – e →Br, Br + Br →Br2

2016

a) In solid state, due to the absence of free ions, sodium chloride cannot conduct electricity. In molten state or in aqueous solution, the electrostatic force of attraction disappears, and ions are set free, and thus, it becomes a conductor of electricity.

b) Na[Ag(CN)2] is a complex salt which dissociates slowly causing uniform deposit of Ag. AgNO3 undergoes fast dissociation causing rough and non-uniform deposit of Ag. Thus AgNO3 is not preferred.

c) Copper conduct electricity only by free electrons in solid state and thus, it is a non-electrolyte.