2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

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Karnataka 2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 1.
What is mineral?
Answer:
Naturally occurring chemical substances in the earth curst obtained by mining are called minerals.

Question 2.
What is an ore?
Answer:
Mineral from which metal can be extracted profitably is called an ore.

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 3.
What is gangue or matrix?
Answer:
Unwanted earthly rocky impurities associated with ore is called gangue or matrix.

Question 4.
What is metallurgy?
Answer:
The scientific and technological process used for isolation of metals from its ore known as metallurgy.

Question 5.
What is concentration of ores?
Answer:
Removal of the unwanted materials like sand, clay, etc. from the ore is known as concentration of ores (ore dressing or benefication of ores).

Question 6.
How ore is concentrated by hydraulic washing? (gravity seperation method).
Answer:
In this process, stream of running water is used to wash the powdered ore. An unwanted lighter gangue particles are washed away and the heavier ores are left behind.

Question 7.
Explain magnetic separation concentration method.
Answer:
This method is used when either the ore or the impurities are magnetic in nature.
2nd PUC chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements 1
The powdered ore is allowed to fall on a belt which moves over two roller’s one of which is magnetic. As the ore particles move over the magnetic roller magnetic particles fall near the roller. Where as non-magnetic particles fall away from the roller due to centrifugal force.

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 8.
Explain froth flotation process.
Answer:
This process is based on the difference in the wetting characteristics of the ore and gangue particles with oil and water.
2nd PUC chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements 2
Powdered ore is suspended into a tank containing water. Pine oil or xanthates (collector) and aniline or cresols (stabilizer) are added. A rotating paddle agitates the mixture and draws air in it. As a result froth is formed which carries the ore particles. This method is suitable for sulphide ores.

Question 9.
What type of ore is concentrated by froth floatation?
Answer:
Sulphide ores.

Question 10.
Name the depressant used to separate two sulphide ores containing ZnS and PbS.
Answer:
Sodium cyanide (NaCN).

Question 11.
Name the process used for the concentration of sulphide ores.
Answer:
forth floatation process.

Question 12.
Describe the three steps involved in the leaching of bauxite to get pure alumina.
Answer:
(a) Bauxite ore is heated with concentrated solution of NaOH at 473K to 523K and 35-36 bar pressure. Al2O3 dissolves out as sodium aluminate leaving behind impurities.
Al2O3 + 2NaOH + 3H2O → 2Na |A1 (OH)4]

(b) The aluminate in solution is neutralised by passing CO2 gas and hydrated Al2O3 is precipitated.
2Na [Al (OH4)] + 2CO2 → Al2O3 3H2O + 2NaHCO3

(c) Hydrated alumina is filtered, dried and heated to give pure alumina.
2nd PUC chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements 3

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 13.
What is roasting? Explain.
Answer:
The process of heating the ore in the presence of excess of air to a high temperature below their melting point.
Roasting is carried out in a reverbaratory furnace. During roasting sulphide ores are converted into oxide ores. .
2ZnS + 3O2 → 2ZnO + 2SO2

Question 14.
What is calcination? Explain.
Answer:
The process of heating the ore to a high temperature below its melting point in the absence of air.
During calcination volatile matter escapes and carbonate ores are converted into oxide ores.
ZnCO3 → ZnO + CO2

Question 15.
Explain the extraction of iron from its ore.
Answer:
2nd PUC chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements 4
Concentrated ore is mixed with lime stone and coke, and fed into blast furnace. Coke acts as fuel, CO formed from it acts as reducing agent and lime stone acts as flux.
Reactions in the blast furnance

1. Zone of combustion : Hot air is blown from the bottom of the . furnance coke burns to give CO2 temperature rises to 2200K.
C + O2 → CO2
The CO2 reacts with overlying coke to from CO.
CO2 + C → 2CO.

(ii) Zone of reduction : In the upper part of the furnance where the temperature range is 500K to 800K CO reduces iron oxides to iron.
Fe2O3 + 3CO → 2Fe + 3CO2

(iii) Zone of slag formation : In the middle part of the furnance where the temperature range is 800K to 1000K limestone decomposes to CaO, which removes silicate impurity to form slag.
CaCO3 → CaO + CO2
CaO + SiO2 → CaSiO3.

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 16.
Among carbon and carbon monoxide, which one is better reducing agent for Fe2O3 above 1000K?
Answer:
Carbon

Question 17.
Among carbon and carbon monoxide which one is better reducing agent for Fe2O3 below 1000K.
Answer:
Carbon monoxide.

Question 18.
What is the role of lime stone in the extraction of iron from the concentrated haematite ore?
Answer:
Flux.

Question 19.
Explain the process of obtaining ‘blister copper’ from copper matte.
Answer:
Copper matte is mixture of cuprous sulphide and little quantity of ferrous sulphide.
Copper matte along with some quantity of silica is taken in converter in which hot air is blown.
(a) Remaining ferrous sulphide oxidises to ferrous oxide, which in turn combines with silica to form slag ferrous silicate
2FeS + 3O2 → 2FeO + 2SO2
FeO + SiO2 → FeSiO3

(b) Part of cuprous sulphide oxidises to cuprous oxide which combines with remaining cuprous sulphide forming blister copper.
2Cu2S + 3O2 → 2Cu2O + 2SO2
2Cu2S + Cu2S → 6Cu + SO2

Question 20.
Write the composition of copper matte.
Answer:
Cu2S + FeS.

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 21.
Name the flux used to remove iron impurity from molten copper matte.
Answer:
Silica or SiO2.

Question 22.
What is the role of silica in the metallurgy of copper?
Answer:
Flux.

Question 23.
Explain the extraction of aluminium by Hall Heroult process.
Answer:
Purified alumina is fused with cryolite and fluospar which lowers the melting point of the alumina. The fused mass is taken in steel vessel lined with carbon lining acts as cathode. Bunch of carbon rods dipped in the molten solution acts as anode.

On electrolysis aluminium is discharged at cathode and oxygen is liberated at anode which reacts with the carbon of the anode producing CO and CO2.
The electrolytic reactions are:
Cathode Al3+ + 3e → Al
Anode C + O-2 → CO + 2e
C + 2O-2 → CO2 + 4e

Question 24.
Draw labelled diagram of Hall-Heroult electrolytic cell for the extraction of aluminium. Write the anode and cathode reactions.
Answer:
Purified alumina is fused with cryolite and fluospar which lowers the melting point of the alumina. The fused mass is taken in steel vessel lined with carbon lining acts as cathode. Bunch of carbon rods dipped in the molten solution acts as anode.

On electrolysis aluminium is discharged at cathode and oxygen is liberated at anode which reacts with the carbon of the anode producing CO and CO2.
The electrolytic reactions are:
Cathode Al3+ + 3e → Al
Anode C + O-2 → CO + 2e
C + 2O-2 → CO2 + 4e

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 25.
In the extraction of aluminium by electrolysis.
1. Give the composition of the electrolyte used.
2. Over all reaction.
3. Role of cryolite.
Answer:
1. Al2O3 + Na3AlF6 + CaF2
2. 2Al2O3 + 3C → 4Al + 3CO2
3. It decreases the melting point of Al2O3.

Question 26.
During the extraction of aluminium by Hall-Heroult process at which m| electrode oxygen gas is liberated.
Answer:
Anode or positive electrode.

Question 27.
Explain the extraction of gold from gold ores by oxidation process.
Answer:
Gold ores are leached with sodium cyanide solution in presence of air. Due to oxidation gold dissolves in sodium cyanide forming complex.
8NaCN + 4Au + 2H2O + O2 → Na[Au(CN)2] + 4NaOH
The metal is recovered by displacement method by adding zinc. .
2Na [Au (CN)2] + Zn → Na2[Zn (CN)4] + 2Au.

Question 28.
Write the chemical reactions involved in the extraction gold using sodium cyanide.
Answer:
Gold ores are leached with sodium cyanide solution in presence of air. Due to oxidation gold dissolves in sodium cyanide forming complex.
8NaCN + 4Au + 2H2O + O2 → Na[Au(CN)2] + 4NaOH
The metal is recovered by displacement method by adding zinc. .
2Na [Au (CN)2] + Zn → Na2[Zn (CN)4] + 2Au.

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 29.
How zinc is obtained by zinc oxide?
Answer:
When zinc oxide is heated with coke at 1673K, coke reduces zinc oxide to zinc
ZnO + C → Zn + CO

Question 30.
Name the reducing agent used in the extraction of zinc from zinc oxide. Give equation.
Answer:
Reducing agent – Coke.
ZnO + C → Zn + CO

Question 31.
Explain electrolytic refining.
Answer:
In this method, impure metal rod is made as cathode and pure metal sheet is made as anode. Suitable salt solution of the same metal is used as an electrolyte. On passing electric current the anode dissolves and pure metal is deposited on the cathode.
At anode : M → Mn+ + ne
At Cathode : Mn+ + ne → M

Question 32.
Explain Zone refining.
Answer:
2nd PUC chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements 5
Crude metal rod is heated from one end.using a circular heater. At this region metal melts, when the heater is moved along the rod. The purest metal solidifies and impurities moves towards molten region.
By repeating the process impurities concentrate at one end of the rod which can be cut off.

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 33.
Name the refining method used to produce semiconductor.
Answer:
Zone refining.

Question 34.
Write the principle involved in the zone refining.
Answer:
The impurities are more soluble in the melt than in the solid state of the metal.

Question 35.
Name the method of refining of silicon.
Answer:
Zone refining.

Question 36.
Explain Mond’s process for refining nickel.
Answer:
Step – 1 : Nickel is heated in a stream of CO forming volatile complex.
2nd PUC chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements 6
Step – 2: This complex on further heating decomposed giving the pure metal.
2nd PUC chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements 7

Question 37.
Explain van Arkel method for refining Zirconium and Titanium.
Answer:
Step -1 : Crude (Zr or Ti) is heated in a evacuated vessel with iodine to form volatile metal iodide.
Zr + 2I2 → ZrI4
Step – 2: The metal iodide is decomposed on a tungsten filament electrically heated to 1800K. The pure metal is thus deposited on the filament.
ZrI4 → Zr + 2I2.

2nd PUC Chemistry Question Bank Chapter 6 General Principles and Processes of Isolation of Elements

Question 38.
Name a metal refined by van Arkel metal.
Answer:
Titanium or Zirconium.