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10th Class - Physical Science-TS

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10th Class - Physical Science-TS
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I. Reflections on concepts

Question 1.
List three metals that are found In nature as Oxide ores.

Answer:
Zinc, Ferrous, Aluminium, and Magnesium are metals which are found in nature as oxide ores.
They are :

Oxide ore Metal Formula
Zincite Zinc ZnO
Haematite Ferrous Fe2O3
Bauxite Aluminium Al23O2H2O
Magnetite Magnesium MgCO3

Question 2.
List three metals that are found in nature n uncombined form.

Answer:

  1. Gold
  2. Platinum
  3. Silver
  4. Copper

Question 3.
Write a note on dressing of ore in metallurgy.

Answer:

  1. Dressing is the first step in extraction of metals.
  2. Ores that are mined from earth are usually contaminated with impurities such as soil and sand etc.
  3. Dressing means, simply getting rid of as much of the unwanted rocky material as possible before the ore is converted into the metal.
  4. Physical methods are used to enrich the ore.
  5. These methods adopted in dressing the ore depend upon difference between physical properties of ore and gangue.
  6. The following physical methods involved in dressing are 1) Hand picking 2) Washing 3) Froth floatation 4) Magnetic separation.
Question 4.
How do metals occur in nature? Give examples to any two types of minerals.

Answer:
The earth’s crust is the major source of metals. Sea water also contains some soluble salts such as sodium chloride and magnesium chloride etc. Some metals like Gold (Au), Silver (Ag) etc., are available in nature in a free state (native) as they are least reactive.

Other metals mostly are found in nature in the combined form due to their reactivity. The elements or compounds of the metals which occur in nature ¡n the earth’s crust are called ‘minerals’. Minerals in oxide form: Bauxite, Zincite, Magnetite, etc.

Question 5.
What is the difference between roasting and calcination? Give one example for each.

Answer:

Roasting Calcination
1. Roasting is a pyrochemical process in which the ore is heated in the presence of air below its melting 1. Calcination ¡s a pyrochemical process in which the ore is heated in the absence of air.
2. The product is metal oxide obtained from sulphide ore. 2. The product is metal oxide, obtained by decomposition of ore.
3. Eg: 2ZnS + 3O22ZnO +2SO2 3. Eg : CaCO3CaO+CO2
Question 6.
Draw the diagram showing i) Froth floatation ii) Magnetic separation.

Answer:
i) Froth floats tian

ii) Magnetic separation

Question 7.
Draw a neat diagram of the Reverberatory furnace and label it neatly.

Answer:

Question 8.
What is an ore? On what basis a mineral is chosen as an ore?

Answer:
Ore: A mineral from which a metal can be extracted economically and conveniently is called ‘ore’.
To choose a mineral as an ore the following are considered

  • The percentage of the metal in that mineral.
  • Whether metal can be profitably extracted from it or not.
  • The convenience of extraction of metal.
Question 9.
Write the names of any two ores of iron.

Answer:

  1. Haematite – Fe2O3
  2. Magnetite – Fe3O4
Question 10.
How do metals occur In nature? Give examples of any two types of minerals.

Answer:
The earth’s crust is the major source of metals. Sea water also contains some soluble salts such as sodium chloride and magnesium chloride etc. Some metals like Gold (Au), Silver (Ag) etc., are available in nature in free state (native) as they are least reactive. Other metals mostly are found in nature in the combined form due to their reactivity.

The elements or compounds of the metals which occur in nature in the earth’s crust are called ‘minerals’.
Minerals in oxide form: Bauxite, Ziricite, Magnetite, etc.
Minerals in sulphide form: Copper iron pyrites, Gatena, etc.

Question 11.
Write short notes on froth floatation process.

Answer:
Froth Floatation process:

Froth Floatation process for the concentration of sulphide ores.

  1. This method is mainly useful for sulphide ores which have no wetting property whereas impurities get wetted.
  2. The ore with impurities is finely powdered and kept ¡n water taken in a floatation cell.
  3. Air under pressure is blown to produce froth in water.
  4. Froth so produced takes the ore particles to the surface whereas, impurities settle at the bottom.
  5. Froth is separated and washed to get ore particles.
Question 12.
When do we use magnetic separation method for concentration of an ore? Explain with an example.

Answer:
Magnetic Separation Method:
If the ore contains impurities such that one, of them, is magnetic and the other is non – magnetic they are separated by magnetic separation method.
Eg: Magnetic ores like iron pyrites, (FeS) and magnetite (Fe3O4) are concentrated by this method. The crushed ore is allowed to pass through electromagnetic belts. The mineral particles are retained and gangue particles are thrown away as a separate heap.

Question 13.
Write short notes on each of the following:

(i) Roasting.
(ii) Calcination.
(iii) Smelting.

Answer:
(i) Roasting:

  • Roasting is a pyrochemical process in which the ore is heated in the presence of oxygen or air below its melting point.
  • The products obtained in the process are also produced in solid state.
  • Generally, reverberatory furnace is used for roasting.
    Eg : 2ZnS + 3O2→ 2ZnO + 2SO2

(ii) Calcination:

  • Calcination is a pyrochemical process in which the ore is heated in the absence of air.
  • The ore gets generally decomposed n the process.
    Eg: MgCO3→ MgO + CO2

(iii) Smelting:

  • Smelting is a pyrochemical process ¡n which the ore is mixed with flux and fuel and strongly heated.
  • The heat is so strong that the ore is reduced to even metal and the metal is obtained in molten state.
  • During smelting, the impurities (gangue) in the ore react with flux to form slag which is removed.
  • The smelting is carried out n a specially built furnace known as blast furnace.
Question 14.
What is gangue and slag?

Answer:

  • Gangue: The impurity present in the ore is called gangue.
  • Slag: A flux is a chemical substance added to convert gangue into fusible mass. This fusible mass is called slag.
    Gangue + Flux Slag

Application of concepts

Question 1.
Magnesium is an active metal, if it occurs as a chloride in nature, which method of reduction is suitable for its extraction?

Answer:
Magnesium is an active metal. If it occurs as chloride in nature, the only method viable to extract magnesium ( any active metal) is electrolysis of fused Magnesium chloride. In electrolysis of fused Magnesium chloride, magnesium is deposited at cathode and chlorine gas is liberated at the anode.
MgCl2→ Mg+2 + 2Cl–
At cathode, Mg+2+ 2e–→ Mg
At anode, 2Cl–→ Cl2 + 2e–

Question 2.
Mention two methods which produce very pure metals from impure metals.

Answer:
Electrolysis and reduction are the two methods which produce pure metals.

Question 3.
Which method do you suggest for extracting of high reactivity metals? Why?

Answer:
High reactivity metals like K. Na, Ca, Mg, etc., can be extracted by electrolysis.
Reasons:

  1. Simple reduction methods like heating with C, CO, etc., to reduce the ores of these metals are not feasible.
  2. The temperature required for the reduction is too high and more expensive.,
  3. Hence electrolysis is the suggestable method to extract high reactive metals.
Question 4.
Explain Thermite process and mention its applications in our daily life.

Answer:
Thermite process

  1. When highly reactive metals such as Na, Ca, Al are used as reducing agents they displace metals of lower reactivity from their compounds.
  2. These displacement reactions are highly exothermic. The amount of heat evolved s so large that the metals produced will be in molten state.
  3. The reaction of iron oxide (Fe2O3), with aluminium is used to join railings of railway tracks or cracked machine parts. This reaction is known as the thermite reaction.
    2Al + Fe2O3→ Al2O3 + 2Fe + Heat

Applications in daily life
1. To join railings of railway tracks.
2. Used to join cracked machine parts.

Question 5.
Where do we use handpicking and washing methods in our daily life? Give examples. How do you correlate these examples with enrichment of ore?

Answer:
We use hand picking in separating stones from rice and da I. We use washing methods to separate dust from rice, dal, vegetables, fruits etc.

Hand-picking: The colour and size of impurities is different from rice or dal. So we can easily separate them by hand-picking. In the same way if the ore particles and the impurities are n different sizes, colour etc., we can see this hand-picking method to separate ore from impurities.

Washing: Less-density particles like dust is separated from more density particles like rice, vegetables etc., by washing. In the same way ore particles are crushed and kept on a slopy surface. They are washed with a controlled flow of water. Less sensitive impurities are carried away by water flow, leaving the more sensitive ore particles behind.

Question 6.
What is activity series? How it helps in extraction of metals?

Answer:
Activity series: The arrangement of the metals in decreasing order of their reactivity is known as ‘activity series’.
Use of Activity series in extraction of metals
1. The method used for a particular metal for the reduction of its ore to the metal depends mainly on the position of the metal in the activity series.
Eg:
The metals at the top of the activity series (highly reactive) can be extracted by electrolysis.
The metals at the middle of the activity series can be extracted by

  • reduction of metal oxide with carbon
  • reduction of oxide ores with Co,
  • self-reduction of sulphide ores
  • reduction of ores with more reactive metals (thermite process).

3. The metals at the bottom of the activity series (less reactive) can be extracted by heating along, and displacement from their aqua solution.

Suggested Experiments

Question 1.
Suggest an experiment to prove that the presence of air and water are essential for corrosion. Explain the procedure.

Answer:
Corrosion: Corrosion is the deterioration of a metal, as a result of chemical reaction between it and the surrounding environment.

Experiment:
Aim: To prove that the presence of air and water are essential for corrosion. Materials required : 3 test tubes, 3 iron nails, oil, water, anhydrous calcium chloride, rubber corks.

Procedure:
1. Take three test tubes and place clean iron nails in each of them.
2. Label these tests tubes A, B and C. Pour some water in test tube A and cork it.
3. Pour boiled distilled water in test tube B, add about 1 ml of oil and cork it. The oil will float on water and prevent the air from dissolving in the water.
4. Put some anhydrous calcium chloride in test tube C and cork it. Anhydrous calcium chloride will absorb the moisture.
5. Leave these test tubes for a few days and then observe.

6. We will observe that ¡ron nails rust in test tube A, but they do not rust in test tubes B and C.
7. In the test tube A the nails are exposed to both air and water whereas in the test tube ‘B’ the nails are exposed to only water and in the test tube ‘C’ the nails are exposed to dry air.
8. This shows air and water are essential for corrosion.

Suggested Projects

Question 1.
Collect information about extraction of metals of low reactivity silver, platinum and gold and prepare a report.

Answer:
Extraction of Silver:

  1. Silver occurs both in combined state as well as In free state. The important ores of silver are Argentite (or) Silver glance (Ag2S) Pyrargyrite (or) Ruby silver 3 Ag2S Sb2S3 silver copper glance (CuAg)2S
  2. Silver is extracted from the ore-Argentite (Ag2S).
  3. The process of extraction of silver is called cyanide process, as sodium cyanide solution is used.
  4. The ore Is crushed, concentrated and then treated with sodium cyanide solution.
  5. This reaction forms sodium argent cyanide [Na[Ag(CN)2]]
    Ag2S + 4 NaCN → 2Na[Ag(CN)2] + Na2S
  6. This solution of sodium argent cyanide combines with zinc dust and forms tetra cyano zincate and precipitated silver. This precipitated silver is called spongy silver.
    Zn + 2Na[Ag(CN)2] → Na2[Zn(CN)4)] + 2Ag
  7. This spongy silver is fused with potassium nitrate to obtain pure silver. Then the silver obtained is purified by electrolytic process.

Extraction of platinum

  • Platinum is rarely found on its own, but In combination with other base and precious metals.
  • The extraction process of platinum is a complex process which includes milling the ore and smelting at high temperatures. This removes base metals notably sulphur and concentrates PGM (Platinum Group Metals) – Gold, Platinum and Palladium.
  • The PGM matter is further processed by electrolysis to remove Nickel, Cobalt and Copper.
  • The high-grade concentrate is treated by solvent extraction, distilling, and ion- exchange treatments to separate the PGMs Into its separated metals.

Extraction of Gold:

  1. Gold is usually found alone or alloyed with mercury or silver.
  2. In all methods of gold ore refining, the ore is usually washed and filtered at the mine, then sent to the mill. At the mill, the ore is ground into smaller particles with water, then ground again in a ball mill to further pulverize the ore.
  3. Several processes can be used to separate the Gold from its ore. They are:

a) Cyanide process:

  • The ground ore Is put In a tank containing a weak cyanide solution and zinc is added.
  • The zinc causes a chemical reaction which separates the gold from the ore.
  • The gold is then removed from the solution with a filter press.

b) Carbon-in-pulp method:

  1. In this method, the ground ore is mixed with water before cyanide Is added. Then carbon is added to bond with the gold.
  2. The carbon-gold particles are put into a caustic carbon solution, separating out the gold.

c) Heap leaching:

  1. The ore is placed on open-air pads and cyanide is sprayed over It, taking several weeks to leach down to an imperious base.
  2. The solution then pours off and pad into a pond and is pumped from there to a recovery plant, where the gold is recovered.
  3. Heap-leaching helps recover gold from ore that would otherwise be to expensive to process.

Page 237

Question 1.
Can you mention some articles that are made up of metals?

Answer:
Utensils in kitchen, window gnUs, pots, chairs, iron gates, bodies of motor cars, etc.

Question 2.
Do metals exist in nature in the same form as that we use ¡n our daily life?

Answer:
No, metals do not exist in nature ¡n the form same as that we use in our daily life.

Question 3.
Have you ever heard the words like ore, mineral and metallurgy?

Answer:
Yes.

Question 4.
Do you know how these metals are obtained?

Answer:
The metals are extracted from their ores mainly in three stages.

  1. The concentration of ore.
  2. Extraction of crude metal.
  3. Refining of the metal.
Question 5.
How the metals are present In nature?

Answer:
The metals are present in nature In combined form as their compounds.

Page 239

Question 6.
What metals can we get from the ore mentioned in Table-1?

Answer:

Question 7.
Can you arrange these metals in the order of their reactivity.

Answer:
K>Na>Ca>Mg>Al >Zn>Fe>Pb>Cu>Ag>Au

Question 8.
What do you notice In table-2?

Answer:
I noticed that the ores of many metals are oxides and sulphides.

Question 9.
Can you think how do we get these metals from their ores?

Answer:
These metals are obtained from their ores by suitable metallurgical processes.

Question 10.
Does the reactivity of a metal and form of its ore (oxides, sulphides, chlorides, carbonates, sulphates) has any relation with process of extraction?

Answer:
Yes, highly reactive metals are obtained by electrolysis from their molten salts, moderately reactive metals are obtained by reducing with suitable reagents whereas least reactive metals are available in native form.

Question 11.
How are metals extracted from mineral ores?

Answer:
Metals are extracted from mineral ores In three steps.

  1. Concentration of ore or Dressing.
  2. Extraction of crude metal.
  3. Refining of the metal.
Question 12.
What methods are to be used?

Answer:
Hand-picking, Washing, Froth floatation and Magnetic Separation methods are to be used.

Page 247

Question 13.
Do you know why corrosion occurs?

Answer:
Metals are stable in the form In which they are available in nature. So by means of corrosion, they change to the form as they occur n nature.

Question 14.
What does this tell us about the conditions under which iron articles rust?

Answer:
Corrosion of iron ( commonly known as rusting ) occurs in presence of moisture and air.

Page 250

Question 15.
What is the role of furnace in metallurgy?

Answer:
A furnace is used for heating the ores and crude metals to required temperatures in metallurgical operations.

Question 16.
How they bear large amounts of heat?

Answer:
The furnaces are lined inside with refractory materials and hence they can bear large amounts of heat.
The substances which are capable of withstanding very high temperatures without melting or becoming soft are called refractory materials.

Question 17.
Do all furnaces have same structure?

Answer:
No, all furnaces do not have same structure.

Activity 1

Question 1.
How do you classify ores based on their formula?

1) Look at the following ores.
2) Identify the metal present in each ore.

Now classify them as shown in the table.

Answer:
Classification of ores as oxides, sulphides, chlorides, carbonates, and sulphates is done as follows.

Activity 2

Question 2.
Show that both air and water are necessary for corrosion of iron.

Answer:

  1. Take three test tubes and place clean iron nails in each of them.
  2. Label these test tubes as A, B and C. Pour cork it.
  3. Pour boiled distilled water in test tube. B Add about 1 ml of oil and cork it. The oil will float on water and prevent the air from dissolving in the water.
  4. Put some anhydrous calcium chloride in test tube C and cork it. Anhydrous calcium chloride will absorb the moisture if any from the air. Leave these test tubes for a few days and then observe.

Observation: Iron nails rust in test tube A but they do not rust in test tubes B and C. In the test tube A the nails are exposed to both air and water. In the test tube B the nails are exposed to distilled water and the nails in test tube C are exposed to dry air only.

Inference: From this we can conclude that both air and water are necessary for corrosion of iron.

Important Question

TS 10th Class Physical Science Important Questions Chapter 11 Principles of Metallurgy
1 Mark Questions

Question 1.
What are minerals?

Answer:
The elements or compounds of the metals which occur in nature in the earths crust are called minerals.

Question 2.
What are ores?

Answer:
The minerals from which the metals are extracted without economical loss are called ores.

Question 3.
Name few highly reactive metals, which are never found in nature in free state.

Answer:
K, Na, Ca, Mg, Al.

Question 4.
Name few moderately reactive metals.

Answer:
Zn, Fe, Pb, Cu.

Question 5.
Name few metals which occur in native state in nature. Why do they occur so?

Answer:
Gold, Platinum and Silver are the metals which occur in native state in nature because of their low chemical reactivity.

Question 6.
What is dressing of an ore?

Answer:
The process of removal of impurities from an ore Is called dressing of the ore or concentration of the ore.

Question 7.
What is activity series?

Answer:
Arranging the metals in the decreasing order of their reactivity is known as activity series
K>Na>Ca>Mg>Al>Zn>Fe>Pb>H>Cu>Hg>Ag>Au
Highly reactive Moderately reactive Less reactive

Question 8.
How do you extract highly reactive metals?

Answer:
Highly reactive metals can be extracted by electrolysis of their fused compounds.

Question 9.
How do you extract moderately reactive metals?

Answer:
These metals are generally present as sulphides or carbonates. They are converted to oxides before reducing them to metals.

Question 10.
What Is roasting? Give an example.

Answer:
The process in which the ore s heated in the presence of oxygen or air below its melting point Is called roasting.
Eg: 2ZnS + 3O2 → 2ZnO + 2SO2

Question 11.
What is calcInation ? Give an example.

Answer:
The process in which the ore is heated in the absence of oxygen or air is called calcination.
Eg: MgCO3 → MgO + CO2

Question 12.
Mention some properties of metals.

Answer:
Malleability, Ductility, Sonarity, Lusture, Electrical conductivity, etc., are some properties of metals.

Question 13.
Define Metallurgy.

Answer:
Metallurgy is the process of extraction of metals from their ores.

Question 14.
What is the major source of metals?

Answer:
Earth’s crust is the major source of metals.

Question 15.
Why do we call the oxygen-sulphur group chalcogen family?

Answer:
We know that most of the ores of many metals are oxides and sulphides. This is why the oxygen-sulphur (16-group) group is called chalcogen furry. (Chalco-oregenus produce).

Question 16.
Arrange the following metals In descending order of their reactivity. K, Zn, Ag, Fe, Ca, Au, Na, Pb.

Answer:
Highly reactive metals: K, Na, Ca
Moderately reactive metals: Zn, Fe, Pb
Low reactive metals: Ag, Au
The descending order of their reactivity: K, Na, Ca, Zn, Fe, Pb, Ag, Au,

Question 17.
What is concentration or dressing?

Answer:
Concentration or dressing means, simply getting rid of as much of the unwanted rocky material as possible before the ore is converted Into the metal.

Question 18.
How to choose a physical method in enriching of the ore?

Answer:
The physical methods adopted in dressing or enriching of the ore depends upon difference between physical properties of ore and gangue.

Question 19.
Give an example for reduction of metal oxide with carbon.

Answer:
The oxides are reduced by coke In a dosed female which gives the metal and carbon monoxide.


Question 20.
Give an example for reduction of oxide ore with CO. (ASI)

Answer:

Question 21.
What is refining?

Answer:
The process of obtaining the pure metal from the impure metal is called refining of the metal.

Question 22.
Mention some important methods of refining.

Answer:
The important methods of refining are.
a) Distillation
b) Poling
c) Liquation
d) Electrolysis.

Question 23.
What is flux?

Answer:
Flux Is a substance added to the ore to remove the gangue from it by reacting with ore. It the impurity is acidic substance, basic substance is used as flux and vice-versa.

Question 24.
What is the role of furnace in metallurgy?

Answer:
The furnace is the one which is used to carry out pyrochemical processes In metallurgy.

Question 25.
Why do we add impurities to electrolytes during electrolytic extraction of metals?

Answer:
A large quantity of electricity is required to keep the ore in molten state, during electrolysis. Hence suitable impurities are added to the ore (electrolyte) to decrease its melting point.

Question 26.
How do various metals In the activity series react with chlorine on heating?

Answer:
All the metals react with chlorine on heating to form their respective chlorides
But the reactivity decreases from top to bottom.

Question 27.
Is Silver is mineral or Ore? Justify your answer.

Answer:
Silver neither mineral nor ore. It Is a metal.

Question 28.
What is Gangue?

Answer:
The impurities obtained during dressing of ore is called gangue.

Question 29.
Where are used the thermite process in daily life?

Answer:
Joining railings of railway tracks.
Joining cracked machine parts.

Question 30.
Give any two examples of ores with their formulas.

Answer:
Bauxite AlO2.2H2O
Magnesite MgCO3

Question 31.
What are the preventive methods do you take for rusting iron materials?

Answer:
Iron materials can be prevented from rusting by
Painting material
Preventing the surface of the iron material to come in contact with atmosphere
Coating the materials with non-rusting materials by electroplating method.
Applying oil to prevent rusting.

Question 32.
How do you know the reactivity of metals with chlorine, decreases from top to bottom?

Answer:
We know that the reactivity of metals with chlorine decreases from top to bottom from the heat evolved when the metal reacts with one mole of chlorine gas to form chloride.

Question 33.
Aluminium occurs in combined state in nature whereas gold Is found In free state. Why?

Answer:
Gold has low reactivity and so occurs In free state. Aluminium is electropositive metal and has high reactivity and occurs as oxide or chloride.

Question 34.
Why is carbon not used for reducing aluminium from aluminium oxide?

Answer:
The oxide of aluminium is very stable and can be reduced by electrolytic process.

Question 35.
An ore gives CO2on treatment with dilute acid. Identify th. ore and name the process that should be used to concentrate this ore.

Answer:
The ore gives CO2 on treatment with dilute acid, therefore It is a carbonate ore. The ore after concentration is converted Into free metal by
CalcInation
Smelting or Reduction or
Electrolybc process

Question 36.
Name two metals other than aluminium which are obtained by electrolytic reduction.

Answer:
Sodium and Magnesium.

2 Marks Questions

Question 1.
Silicon Is a metalloid. How do you support this?

Answer:
Silicon exhibits following properties, so I conclude that it is a metalloid.
It has metallic lustre by nature.
It exists in several metallic and non-metallic compounds.
It is brittle in nature.
All metalloids are usually occurs in combined states both metals and non-metals.

Question 2.
Mention the most important metals and non-metals from the following products.
a) Annapurna salt
b) Liquid used in thermometer
c) Lead of the pencil
d) Chlorophyll
e) Filament in electric bulb
f) Enamel layer on teeth

Answer:
a) Annapurna salt: Iodine, chlorine: Non-metals
b) Liquid used in thermometer: Mercury: Metal
c) Lead of the pencil: Graphite: Non-metal
d) Chlorophyll : Magnesium: Metal
e) Filament in electric bulb: Tungsten: Metal
f) Enamel layer on teeth: Calcium phosphate: Non-metal

Question 3.
Identify the metal present In the following Ores.
i) Epsom Salt
ii) Horn Silver
iii) Cinnabar
iv) Galena

Answer:
i) Magnesium
ii) Silver
iii) Mercury
iv) Lead

Question 4.
What Is meant by extraction of metals?

Answer:
The separation of metals from ores Is called extraction of metals.

Question 5.
Write the chemical equations of thermite reactions.

Answer:
2Al + Fe2O3 → Al2O3 + 2Fe + Heat
2Al + Cr2O3 → Al2O3 + 2Cr + heat

Question 6.
Give an example of auto reduction of sulphide ores.

Answer:
In the extraction of Cu, from its sulphide ore, the ore is subjected to partial roasting in air to give its oxide.
2Cu2S + 3O2→ 2Cu2O+ 2SO2
When the supply of air Is stopped and the temperature Is raised, the rest of the sulphide reacts with oxide and forms the metal and SO2
2Cu2O + Cu2S → 6Cu + SO2

Question 7.
Explain the process of hand-picking.

Answer:
If the ore particles and the impurities are different in one of the properties like colour, size, etc., the ore particles are hand-picked, using that property. Thus, the metal particles are separated from their impurities.

Question 8.
What is the role of washing In enriching the ore?

Answer:
Washing is one of the physical methods la enriching the ore.
Ore particles are crushed and kept on a sloppy surface. They are washed with controlled flow of water.
Less sensitive impurities are carried away by water flow leaving the more dense ore particles behind.

Question 9.
Write the reactions inside a blast furnace.

Answer:
The reactions inside a blast furnace are :
2C (Fuel) +O2 → 2CO
Fe2O3 (Haemette)+ 3C0 → 2Fe + 3CO2


Question 10.
Do all furnaces have same structure? Explain.

Answer:
Different furnaces have different structures.
In a blast furnace, both firebox and hearth are combined in bg chamber, which accommodates both ore and fuel. It has a cup and cone arrangement at its top to send the ore Into the furnace.
Reverberatory furnace has both firebox and hearth separated, but the flames obtained due to the burning of the fuel touch the ore in the hearth and heat it.
In furnaces like retort furnaces, there is no direct contact between the hearth and firebox and even the flames do not touch the ore.

Question 11.
How do various metals in activity series react with steam?

Answer:
The metals from potassium to iron displace H2 (Hydrogen gas) from steam with decreasing reactivity. That means the reaction of potassium with steam is violent but the reaction of iron Is very slow. The metals from lead to gold are unable to displace hydrogen from steam.

Question 12.
How do various metals in the activity series react with dilute strong acids?

Answer:
1) The metals from potassium to lead displace hydrogen from dilute strong acids with decreasing reactivity.
a) The reaction of potassium is explosive
b) The reaction of magnesium is vigorous
c) The reaction of Iron is steady
d) The reaction of lead is slow
2) The metals from copper to gold do not displace H, from strong dilute acids.

Question 13.
How do you reduce purified ore to the metal of the top of activity series? Explain.

Answer:
The reduction of ore to particular metal mainly depends on position of metal in the activity senes.
Extraction of metals at the top of activity series
Simple chemical reduction methods like heating with C, CO etc., to reduce the ores of the metals are not possible with metals like K, Na, Ca, Mg and Al.
The temperature required for the reduction is too high and more expensive.
The only method used to extract these metals is by electrolysis of their fused compounds.

Question 14.
What are the preventive techniques used in corrosion of metals?
(OR)
Write two precautions to prevent corrosion of metals in your daily life.

Answer:
Prevention of corrosion of metals
Covering the surface of metal with paint or by some chemicals like bisphenol which prevent the surface of the metallic object to come In contact with atmosphere.
Covering the surface of metal by other metals like tin or zinc that are Inert or react themselves with atmosphere to save the metal.
An electrochemical method in which a sacrificial electrode of another metal like magnesium and zinc etc., corrodes itself to save the metal.

Question 15.
Give some examples for corrosion.

Answer:
Examples for corrosion:
The rusting of iron (Iron oxide)
Tarnishing of silver (Silver sulphide)
Development of green coating on copper (Copper carbonate) and bronze.

Question 16.
What is 22-carat gold? Why It Is preferred for making jewellery?

Answer:
Pure gold, known as 24-carat gold is very soft.
So it is not suitable for making jewellery.
It is alloyed with either silver or copper to make it hard.
So they use 22-carat gold m which pure gold is alloyed with 2 parts of either sliver or copper for making gold jewellery.

Question 17.
Write about the electrolysis of NaCl.

Answer:
1) Fused NaCI is electrolysed with steel cathode and graphite anode.
2) The metal sodium (Na) will be deposited at cathode and chlorine gas liberates at the anode.
At Cathode : 2 Na+ + 2e- → 2Na
At Anode: 2Cl- → Cl2 + 2e-

Question 18.
What is a furnace? Explain various parts of furnace.

Answer:
Furnace: Furnace Is the one which is used to carry out pyrochemical processes in metallurgy.
Furnace has mainly three parts :
Hearth: The hearth is the place inside the ore is kept for hearting.
Chimney: ChImney is the outlet through which flue (waste) gass o out of the furnace.
Firebox: Firebox is the part of the furnace where the fuel is kept for burning.

Question 19.
Why alloying s preferred for metals? Explain with examples.

Answer:
Alloying is a method of improving the properties of a metal. We can get desired properties by this method.
For example, iron is the most widely used metal. But it Is never used In its pure state.
This is because pure Iron Is very soft and stretches easily when hot.
But, if it is mixed with a small amount of carbon, It becomes hard and strong.
When iron is mixed with nickel and chromium we get stainless steel which is not corrosive.

4 Marks Questions

Question 1.
The results of reactions of metals A, B, C, D, and E with different solutions are given In the table below. Observe the table and write answers.

a) Which Is the highly reactive metal? Why?
b) Which is the least reactive metal? Why?
c) Which metals form brown layer?
d) Arrange the metals A, B, C, D, E In the order of their reactivity?

Answer:
a) Metal ‘E’ is more reactive among all the metals given because it displaces all the elements from the compounds given In the table.
b) Metal ‘C is the least reactive metal because it does not displace any other metal from the compounds given in the table.
c) Metals B and E will form brown layer.
d) The ascending order is as follows C < A < D < B < E.

Question 2.
Explain purification or refining of crude metal.
(OR)
Write the short notes on each of the following.

a) Distillation
b) Poling
C) Liquation
d) Electrolysis
(OR)
State the methods used to the purification of crude metals. Explain In which context these methods are used.

Answer:
1) The process of obtaining the pure metal from the impure metal is called refining of the metal.
2) Some of the processes of refining are
Distillation
Poling
Liquation
Electrolytic refining.
3) The process that has to be adopted for purification of a given metal depends on the nature of the metal and its Impurities.
i) Distillation: This method is very useful for purification of low boiling ‘metals like zinc (Zn) and mercury (Hg) containing high-boiling metals as impurities: The extracted metal in the molten state ¡s distilled to obtain the pure metal as distillate.
ii) Poling: The molten metal Is stirred with logs of green wood: The impurities are removed either as gases or they get oxidized and form sum (slag) over the surface of the molten metal. Blister copper is purified by this method.
iii) Liquatlon: In this method, a low-melting metal like Tin can be made to flow on a slope surface to separate it from high-melting impurities.
iv) Electrolytic refining:
1. In this method, the impure metal is made to act as anode.
2. A strip of the same metal in pure form is used as cathode.
3. They are put in a suitable electrolytic bath containing soluble salt of the same metal.
4. The required metal gets deposited on the cathode in the pure form.
5. The metal constituting impurity, goes as the anode mud. The reactions are:
At anode: M → Mn++ n.e
At cathode: Mn++ n. e- → M
(M = pure metal, n 1, 2, 3,)

Question 3.
Write the physical methods used for the concentration of the ore. Explain the method used for concentration of the sulphide ore.

Answer:
Methods used for the concentration of ore:
Hand-picking
Washing
Froth flotation
Magnetic separation
Forth flotation process is used for concentration of sulphide ore.
Froth Flotation process

Froth Floatation process for the concentration of sulphide ores
This method ¡s mainly useful for sulphide ores which have no wetting property where as impurities get wetted.
The ore with impurities is finely powdered and kept In water taken in a floatation cell.
Air under pressure Is blown to produce froth In water.
Froth so produced takes the ore particles to the surface whereas, impurities settle at the bottom.
Froth is separated and washed to get ore parties.

Question 4.
What Is corrosion? Explain the chemistry of corrosion. (or) Explain the process involved In corrosion.

Answer:
Corrosion: Corrosion is the deterioration of a metal as a result of chemical reaction between it and the surrounding environment.
Chemistry of corrosion:
1. The chemistry of corrosion in quite complex but it may be considered essentially as an electrochemical phenomenon.
2. During corrosion at a particular spot on the surface of an object made of iron, oxidation takes place and that spot behaves as anode.
Anode : 2Fe → 2 Fe2+ + 4e-
3. Electrons released at this anodic spot move through the metal and go to another spot on the metal and reduce oxygen at that spot in presence of H+.
4. This spot behaves as cathode with the reaction.
Cathode : O2 + 4H+ + 4e- → 2H2O
5. The overall reaction is: 2Fe + O2 + 4H+ → 2Fe2+ + 2H2O
6. The ferrous ions (Fe2+)are further oxidised by atmospheric oxygen to ferric Ions (Fe3+) which come out as rust In the form of hydrated ferric oxide (Fe2O3. XH2O) and with further production of hydrogen ions.

Question 5.
How do you extract metals In the middle of activity series?

Answer:
Extraction of metals In the middle of the activity series:
The ores of these metals are generally present as sulphides or carbonates. Therefore prior to reduction of ores of these metals, they must be converted into metal oxides.
The metal oxides are then reduced to the corresponding metals by using the following methods:
1. ReductIon of metal oxides with carbon: The oxides are reduced by coke in closed furnace which gives the metal and carbon monoxide (CO).

2. ReductIon of oxide ores with CO:

3. Auto (self) reduction of sulphide ores: In the extraction of copper (Cu) from its sulphide ore, the ore is subjected to partial roasting In air to give its oxide.
2Cu2S + 3O2 → 2Cu2O + 2SO2
When the supply of air Is stopped and Increase temperature results in the reaction of rest of sulphide ore with oxide to form metal and SO3.
2Cu2O + Cu2S → 6Cu + SO2
4. Reduction of ores (compounds) by more reactive metals: When highly reactive metals such as sodium, calcium, aluminium etc., are used as reducing agents, they displace metals of low reactivity from the compound.


Question 6.
How do you extract metals at the bottom of the activity series?

Answer:
1. Metals at bottom of the activity series are often found in free state.
2. The oxides of these metals can be reduced to metals by heat alone and sometimes by displacement from their aqueous solutions.
3. When cinnabar (HgS) is heated In air, It s converted into HgO, then reduced to mercury on further heating.

4. Displacement from aqueous solution. When Ag2S is dissolved in KCN solution it forms di cardio argentite (1) ions. From these ions by treating with Zn dust powder Ag is precipitated.
Eg : Ag2S + 4CN- → 2[Ag(CN)2)]- + S2-
2 [Ag(CN)2]-(aq) + Zn(s) → [Zn(CN)4]2-(aq) + 2Ag(s)

Question 7.
Draw the diagram of blast furnace and label it parts.

Answer:

Question 8.
What are various types of furnaces? Explain.

Answer:
Various types of furnaces:
Blast furnace: Blast furnace has both firebox and hearth are combined in big chamber which accommodates both ore and fuel.
Reverberatory furnace: It has both firebox and hearth separated. but the vapours(flame) obtained due to burning of the fuel touches the ore in the hearth and heat it.
Retort furnace: In this furnace, there is no direct contact between the hearth or fire box and even the flames do not touch the ore.
Do You Know?
Alloying is a method of improving the properties of a metal. We can get desired properties by this method. For example, iron is the most widely used metal. But it ¡s never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with a small amount of carbon, it becomes hard and strong. This alloy is called steel.
When iron is mixed with nickel and chromium we get stainless steel which will not rust.
Pure gold, known as 24-carat gold, is very soft. It is, therefore, not suitable for making jewellery. It is alloyed with either silver or copper to make it hard. Generally in India, 22-carat gold is used for making ornaments. It means that 22 parts of pure gold is alloyed with 2 parts of either silver or copper. (Page 248)

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