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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 Electrolysis||Arrhenius 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 dissociation||Electrolytic ionization|
|Separation of ions which are already present in the compound.||Formation of ions from molecules which are not initially in ionic state.|
|Positively charged ion||Negatively charged ion|
|Electrolytic dissociation||Thermal dissociation|
|Breaking of a compound by passing electricity||Breaking a compound by heating it|
|Strong electrolyte||Weak 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.|
|A salt which is a weak electrolyte||Ammonium carbonate|
|A base which is a weak electrolyte||Calcium hydroxide|
|An inert electrode and an active electrode||Pt and Ag respectively|
|A positively charged non-metallic ion||H+|
|The electrode at which reduction occurs||Cathode|
|A non-metallic element which is a conductor of electricity||NH4+|
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 electrolytes||Weak electrolytes||Non-electrolytes|
|Dilute hydrochloric acid||Acetic acid||Carbon tetrachloride|
|Sodium acetate||Ammonium chloride|
|Dilute sulphuric acid||Ammonium 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.
|i) Molten ionic compound||B(strong electrolyte)|
|iii)An Aluminium wire||D(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 molecules||A(non-electrolyte)|
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:
- OH– and SO42-
- Water and oxygen. OH– – e–→[OH], 4[OH]→2H2O + O2
- Hydrogen. H+ + e–→H, H + H →H2
- As both oxygen and hydrogen are colorless gases.
- 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.
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.
|i) Silver plating of a spoon||Plate of pure and clean Ag||Sodium argentocyanide solution||Article to be electroplated|
|ii) Purification of copper||Impure Cu||Copper sulphate solution with few drops of sulphuric acid||Pure copper strip|
|iii)Extraction of sodium||Graphite||Molten NaCl||Iron|
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
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
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+
a) iv) Lead Bromide
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
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
|Copper Sulphate Solution||Copper Metal|
|Aqueous solution||Solid state|
a) iv) Aq acetic acid
b) 1→iii, 2→i, 3→ii
c) Furnish ions Na2+, Cl–, H+, OH–
d) i) Cu2+
v) Plate of pure and clean Ag
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
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
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
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.