Chapter 8.5 – Metallurgy

Metallurgy
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Book Name : Madhyamik Physical Science And Environment
Subject : Physical Science
Class : 10 (Madhyamik)
Publisher : Oriental Book Company Pvt. Ltd
Chapter Name : Physical and Chemical Properties of Matter

In-text Questions

Question 8.5.1

Mention one use of each (a) cast iron (b) steel (c) wrought iron. 

Answer

Metal Use
Cast iron Pipes, machinery, engine blocks, cookware
Steel Buildings, bridges, automobiles, ships, cutlery
Wrought iron Gates, fences, railings, decorative items

Question 8.5.2

Mention the use of copper

Answer

Here are some uses of copper:

  1. Electrical wiring: Copper is an excellent conductor of electricity and is commonly used in electrical wiring.
  2. Plumbing: Copper pipes are widely used in plumbing due to their durability, corrosion resistance, and ability to handle high temperatures and pressures.

Question 8.5.3

What are coinage gold and jewellery gold?

Answer

Coinage gold refers to the gold alloy used to make coins. This alloy is composed of 90% gold and 10% copper. In other countries, the composition may be different. Coinage gold is designed to be hard and durable so that coins can withstand handling and circulation.

Jewellery gold, on the other hand, refers to the gold alloy used to make jewellery. This alloy is also typically 90% gold, but the other 10% is made up of a mix of other metals such as silver, copper, nickel, and zinc.

Question 8.5.4

Mention some uses of zinc. 

Answer

Here are some uses of zinc:

  1. Zn-granules and dusts are used as reducing agent.
  2. To prepare battery
  3. To prepare alloy.

Question 8.5.5

Mention two main uses of aluminium. 

Answer

Two main uses of aluminum are:

  1. To prepare many alloys
  2. Used for metal extraction in thermite process.
  3. Used to wrap cigarettes, chocolate and medicines.

Question 8.5.6

Mention the composition of the following alloys. (a) Mitsch metal (b) Bell metal (c) german silver (d) Duralumin. 

Answer

Alloy Composition
Mitsch metal 50% Cu, 12% Ni, 12% Zn, 25% Sn, and 1% Pb
Bell metal 80% Cu and 20% Sn
German silver 60% Cu, 20% Ni, and 20% Zn
Duralumin 95% Al, 4% Cu, 0.5% Mg, and 0.5% Mn (with traces of other impurities)

Question 8.5.7

What is the difference between minerals and ores ? 

Answer

Minerals Ores
Naturally occurring substances Naturally occurring substances
May or may not contain metal Contain high concentration of metal
May or may not be economically important Economically important for metal extraction
Do not require any extraction process Require extraction process to obtain metal

Question 8.5.8

Petroleum is found under the earth’s surface; is it a mineral?

Answer

Petroleum is not considered a mineral as it is not a naturally occurring solid inorganic substance with a definite chemical composition and crystalline structure. Petroleum is a complex mixture of hydrocarbons, which are organic compounds made up of carbon and hydrogen.

Question 8.5.9

Explain with example, oxidation and reduction take place simultaneously.

Answer

Redox reaction is a reaction in which oxidation and reduction take place simultaneously.

For example: The formation of Magnesium oxide from Mg and O2 is a redox reaction.

2Mg + O2 = 2MgO

Here magnesium is oxidised by loss of two electrons per atom to form Mg2+ ion and oxygen gains two electrons per atom O2- ion.

2Mg – 4e → 2Mg2+ (Oxidation)

O2 + 4e → 2O2- (reduction)

Question 8.5.10

The extraction of metal from its ore is a reduction process, explain. 

Answer

The extraction of metals from their ores involves reduction processes. In a reduction process, a reducing agent is used to remove the oxygen from the metal oxide, which results in the formation of pure metal.

For Example:

The extraction of zinc from its ore involves a reduction process because the metal ions in zinc oxide (ZnO) are reduced to elemental zinc (Zn). This reduction process involves the use of carbon as a reducing agent, which reacts with the oxygen in the zinc oxide to produce carbon dioxide (CO2) and elemental zinc (Zn):

ZnO + C → Zn + CO2

Question 8.5.11

What is the thermite process? 

Answer

The thermite process is a highly exothermic reaction used for the production of pure metals or their alloys. In this process, a metal oxide is reduced by a more reactive metal, typically aluminium, which results in the production of pure metal and aluminium oxide as a byproduct. The reaction is initiated by heating the mixture of reactants to a high temperature, typically around 3000°C, using a suitable ignition source.

Question 8.5.12

Mention the application thermite process. 

Answer

The thermite process has several applications, some of which are:

  1. Welding: The intense heat generated by the exothermic reaction of the thermite mixture can be used for welding. This process is used in rail welding, where a thermite mixture is used to weld two pieces of rail together.
  2. Cutting: The thermite mixture can also be used for cutting metals. When a thermite mixture is ignited, it produces a stream of molten metal that can cut through other metals. This process is used in the demolition of large structures like buildings and bridges.

Question 8.5.13

Rusting is an electrochemical process, explain. 

Answer

Rusting is a process of corrosion in which a metal reacts with oxygen and moisture in the presence of an electrolyte to form hydrated metal oxides. The process involves the transfer of electrons between metal, water, and oxygen, which makes it an electrochemical process.

Question 8.5.14

At the cathode region of the electrochemical cell on the iron surface how the dissolved O2 is reduced? 

Answer

At the cathode region of an electrochemical cell on an iron surface, dissolved O2 is reduced by accepting electrons from the cathode. The oxygen molecule receives two electrons from the cathode and combines with two protons (H+) from the acidic solution to form water (H2O). This reaction is represented as:

O2 + 2H+ + 2e → H2O

Question 8.5.15

How does magnesium protect against rusting on the iron surface? 

Answer

Magnesium can protect against rusting on the iron surface by acting as a sacrificial anode. When magnesium is attached to the iron surface, it undergoes corrosion instead of iron. The magnesium atoms lose electrons and get oxidized, while iron atoms gain electrons and are reduced. As a result, the magnesium metal corrodes instead of the iron surface, preventing rust formation on the iron surface.

Question 8.5.16

What do you mean by cathodic protection?

Answer

Cathodic protection is a technique used to prevent the corrosion of a metal surface by making it a cathode of an electrochemical cell. In this method, a more reactive metal (e.g., magnesium or zinc) is connected to the metal surface to be protected and is made the anode. This causes the more reactive metal to corrode instead of the protected metal, as it becomes the site for oxidation reactions.

Question 8.5.17

Mention few methods of prevention of rusting.

Answer

Rusting of iron can be prevented by the following two ways:

  1. Coating the surface of the iron with paint
  2. Applying grease or oil on the surface of iron

Question 8.5.18

In the activity series of metals, what are the positions of Zn, Al, Fe and Cu from top to bottom? 

Answer

The positions of Zn, Al, Fe, and Cu from top to bottom are:

Zinc > Aluminum > Iron > Copper

Question 8.5.19

Although Zn and Al are above Fe in the activity series of metals, Fe quickly rusts and corrodes but Zn and Al do not. Give reason.

Answer

Zinc and aluminium are more active metals than iron, but they don’t rust easily because they create a shield of oxide on their surface. This shield protects them from coming into contact with water and air, which can cause rusting. Iron, on the other hand, produces a less strong shield, and it can break off, leaving iron exposed and causing rusting.

Multiple Choice Questions (MCQ)

Question 1

Which is the more pure iron?

  1. Cast iron
  2. Pig iron
  3. Steel
  4. Wrought iron

Answer

(d) Wrought iron

Explanation:

Wrought iron is a form of commercial iron that is almost entirely pure iron (Fe), with very low carbon content (less than 0.1%) and other impurities such as sulfur and phosphorus.

Question 2

Which is extensively used for making aeroplane body?

  1. Zn
  2. Cu
  3. Fe
  4. Al

Answer

(d) Al

Explanation:

Aluminum (Al) is extensively used for making aeroplane bodies due to its unique combination of properties, such as being lightweight, corrosion-resistant, and strong.

Question 3

Which alloy does not contain copper?

  1. Mistch metal
  2. Bell metal
  3. German silver
  4. Delta metal

Answer

(a) Mistch metal

Explanation:

German silver, Delta metal, and Bell metal all contain copper as one of their primary components. Mistch metal, on the other hand, is an alloy that does not contain copper.

Question 4

Percentage of silver in German silver is?

  1. 55
  2. 0
  3. 0.5
  4. 24

Answer

(b) 0

Explanation :

German silver, also known as nickel silver, is a copper alloy with nickel and often zinc or other metals. It does not contain silver, despite its name. Therefore, the percentage of silver in German silver is 0%.

Question 5

Which is not a mineral?

  1. Sulphur
  2. Hematite
  3. Petroleum
  4. Zincite

Answer

(c) Petroleum

Explanation:

Petroleum is not a mineral. It is a naturally occurring, flammable liquid found in geological formations in the Earth’s crust. Minerals are inorganic solids with a specific chemical composition and crystalline structure that occur naturally in the Earth’s crust.

Question 6

Electrolysis of molten NaCl produces Na and Cl2, here ?

  1. Na is oxidised
  2. Cl is oxidised 
  3. Both are oxidised
  4. None of these are oxidiced or reduced.

Answer

(b) Cl is oxidised

Explanation:

In the electrolysis of molten NaCl, the chloride ions (Cl) are oxidized at the anode to form chlorine gas (Cl2), and the sodium ions (Na+) are reduced at the cathode to form sodium metal (Na).

Question 7

In the thermite process which is used as a reducing agent?

  1. carbon
  2. iron
  3. aluminium
  4. Zinc

Answer

(c) Aluminium

Explanation:

In the thermite process, aluminium is used as a reducing agent. The thermite reaction involves the exothermic oxidation of aluminium metal in the presence of a metal oxide, such as iron oxide (Fe2O3), to produce molten metal and aluminium oxide (Al2O3).

Question 8

In cathodic protection of iron, which is acting as an anode?

  1. iron
  2. Magnesium
  3. Platinum
  4. H2O

Answer

(b) Magnesium

Explanation:

In the cathodic protection of iron, another metal with a more negative electrode potential is used as the anode to protect the iron from corrosion. Typically, a more reactive metal such as magnesium or zinc is used as the anode.

Question 9

The green patches form on the surface of copper is –

  1. CuSO4
  2. Cu(OH)2
  3. CuO
  4. CuSO4.3Cu(OH)2

Answer

(d) CuSO4.3Cu(OH)2

Explanation:

The green patches formed on the surface of copper are due to the formation of copper carbonate (CuCO3) or copper hydroxide (Cu(OH)2), which are the result of the reaction of copper metal with atmospheric carbon dioxide and moisture.

Fill up the blanks with words given in the brackets

Question
  1. The metal used to build aeroplane body is ____. (Al / Cu) 
  2. Reducing agent used in thermite process is ____. (Al / Zn) 
  3. Bell metal contains ____ + _____ (Cu+Sn) / (Al + Mg)
  4. Bauxite is ____. (Al2O3, 2H2O / Cu2S, FeS2
  5. Extraction of metal from its ore is ____ process. (oxidation / reduction) 
  6. In the cathodic protection of iron Mg acts as ____. (cathode / anode)

Answer

  1. The metal used to build aeroplane body is Aluminium (Al).
  2. The reducing agent used in the thermite process is Aluminium (Al).
  3. Bell metal contains Copper (Cu) and Tin (Sn) – the typical composition is around 80% Cu and 20% Sn.
  4. Bauxite is Al2O3, 2H2O.
  5. Extraction of metal from its ore is Reduction process.
  6. In the cathodic protection of iron, Mg acts as the anode.

Which of the statements is true or false

Question

  1. Extraction of metals from its ore is an oxidation process. 
  2. Pure iron does not rusts. 
  3. The alloy bell metal contains copper. 
  4. Presence of Cl ion accelerates rusting. 
  5. Aluminium corrodes easily by formation Al2O3 on its surface.

Answer

  1. False
    The extraction of metals from their ore is a reduction process.
  2. True
  3. True
  4. True
  5. False.
    Aluminum does not corrode easily by forming Al2O3 on its surface. In fact, aluminium forms a thin and protective layer of aluminium oxide (Al2O3) on its surface that prevents further corrosion.

Answer the following questions

Question 1

Which type of iron is brittle? 

Answer

White cast iron is brittle.

Question 2

The wire of the piano is made by which type of iron? 

Answer

Piano wire is typically made of high-carbon steel.

Question 3

Write the components of German silver. 

Answer

German silver is 50-60% copper, 20-30% zinc, and 10-30% nickel.

Question 4

Galvanisation on the iron sheet is done with which metal?

Answer

Galvanization on the iron sheet is done with zinc metal.

Question 5

Which metal powder is used in paints? 

Answer

Aluminium powder is often used as a metallic pigment in paints.

Question 6

Write the contents of Bell metal. 

Answer

Bell metal is an alloy of copper and tin, typically containing around 80% copper and 20% tin.

Question 7

The name of the ore bauxite is of which metal? 

Answer

The ore bauxite is of aluminium metal.

Question 8

What is the composition of the thermite mixture? 

Answer

The composition of the thermite mixture is typically a metal powder, usually aluminium, mixed with a metal oxide, typically iron oxide (Fe2O3) or copper oxide (CuO).

Question 9

What is rust?

Answer

Rust is a reddish-brown coating that forms on the surface of iron or steel when it reacts with oxygen and moisture in the air.

Question 10

The iron pillar of Gupta age at Delhi does not rust, why ?

Answer

The iron pillar of Gupta age at Delhi does not rust because it is made of a high-quality, corrosion-resistant type of wrought iron that contains a low percentage of phosphorus.

Match the Column-1 with Column-2

Column-1 Column-2
1. Cast lorn (a) spark lighter
2. Copper (b) Zinc
3. Metal extraction from ore (c) Bell metal
4. Galvanisation (d) Fe
5. Mitsch metal (e) Reduction

Answer

Column 1 Column 2
Cast iron (d) Fe
Copper (c) Bell metal
Metal extraction from ore (e) Reduction
Galvanisation (b) Zinc
Misch metal (a) Spark lighter
C. Short Answer type Questions

Question 1

What is galvanization?

Answer

Galvanization is a corrosion protection process used to safeguard iron and steel from rust and other forms of corrosion. It involves applying a layer of zinc to the surface of the metal. This zinc coating acts as a barrier, preventing moisture, oxygen, and other corrosive elements from coming into direct contact with the underlying iron or steel. As a result, galvanized materials are significantly more resistant to rust and corrosion than untreated metals.

Question 2

Write the use of cast iron. 

Answer

Cast iron is used for making pipes, stoves, machine parts, cylinder blocks, and engine blocks due to its high strength, hardness, and wear resistance.

Question 3

Write the use of copper. 

Answer

Uses of copper

  • It is used in electrical wiring and plumbing due to its excellent conductivity and corrosion resistance.
  • Copper is also used in construction due to its strength and durability.

Question 4

What are ores?

Answer

Ores are naturally occurring rocks or minerals that contain valuable metals, minerals, or elements that can be extracted and processed for various industrial or economic purposes.

Question 5

Hematite is the ore of iron, but iron pyrites is not, why? 

Answer

Iron pyrites (FeS2) is not an ore of iron because it does not contain a sufficient amount of iron. Hematite (Fe2O3) is an ore of iron because it contains a high percentage of iron in its composition.

Question 6

Define oxidation and reduction. 

Answer

Oxidation is a chemical reaction where a substance loses electrons.

Reduction is a chemical reaction where a substance gains electrons.

Question 7

What is the principle of the thermite process? 

Answer

The thermite process is based on the principle of exothermic oxidation-reduction reaction between a metal oxide and a metal in which the metal oxide is reduced to the metal, and the metal is oxidized to form a metal oxide with the release of a large amount of heat energy.

Question 8

What happens when a Zinc plate is immersed in an aqueous CuSO4 solution? 

Answer

When a Zinc plate is immersed in an aqueous CuSO4 solution, Zinc metal reacts with CuSO4 to form Zinc sulfate (ZnSO4) and Copper metal (Cu) is deposited on the surface of the Zinc plate due to the displacement reaction. The chemical equation for the reaction is:

Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq)

Question 9

How does magnesium protect iron from rusting? 

Answer

Magnesium is more reactive than iron, so when it’s placed near iron, it corrodes preferentially and protects the iron from rusting. This process is called cathodic protection.

Question 10

Why pure iron does not rusts ?

(Hint : Rusting is an electrochemical process, without impurity formation voltaic cell is not possible.)

Answer

Pure iron does not rust because rusting is an electrochemical process that requires the presence of both oxygen and moisture to form a voltaic cell. Without impurities, pure iron cannot form a voltaic cell and therefore cannot undergo rusting.

Long Answer (LA) type Questions

Question 1

Mention the uses of different types of iron. 

Answer

Type of Iron Uses
Wrought Iron Used in making chains, agricultural tools, ornamental ironwork
Cast Iron Used in making pipes, stoves, engine blocks
Steel Used in making construction materials, machinery, tools, automobiles

Question 2

Distinguish between ores and minerals with example.

Answer

Ores Minerals
Ores are rocks or minerals from which a valuable substance can be extracted at an affordable cost. Minerals are naturally occurring substances that have a definite chemical composition and crystal structure.
Ores typically contain high concentrations of the desired substance. Minerals may or may not contain valuable substances in economically recoverable quantities.
Examples of ores include bauxite (aluminium), haematite (iron), and chalcopyrite (copper). Examples of minerals include quartz, feldspar, and mica.

Question 3

All ores are minerals but all minerals are not ores, explain. 

Answer

All ores are minerals because they are naturally occurring substances that are mined from the earth. However, not all minerals are ores because an ore is a mineral that contains a high enough concentration of a valuable element or compound that it can be economically extracted. Therefore, some minerals may not have any commercial value and are not considered ores.

Question 4

Explain the redox process with example. 

Answer

Redox reaction is a reaction in which oxidation and reduction take place simultaneously.

For example: The formation of Magnesium oxide from Mg and O2 is a redox reaction.

2Mg + O2 = 2MgO

Here magnesium is oxidised by loss of two electrons per atom to form Mg2+ ion and oxygen gains two electrons per atom O2- ion.

2Mg – 4e → 2Mg2+ (Oxidation)

O2 + 4e → 2O2- (reduction)

Question 5

The extraction of metals from their ores are reduction process, explain. 

Answer

The extraction of metals from their ores involves reduction processes. In a reduction process, a reducing agent is used to remove the oxygen from the metal oxide, which results in the formation of the pure metal.

For Example:

The extraction of zinc from its ore involves a reduction process because the metal ions in zinc oxide (ZnO) are reduced to elemental zinc (Zn). This reduction process involves the use of carbon as a reducing agent, which reacts with the oxygen in the zinc oxide to produce carbon dioxide (CO2) and elemental zinc (Zn):

ZnO + C → Zn + CO2

Question 6

Write notes about the thermite process, and mention its application. 

Answer

The thermite process is a highly exothermic reaction used for the production of pure metals or their alloys. In this process, a metal oxide is reduced by a more reactive metal, typically aluminum, which results in the production of pure metal and aluminium oxide as a byproduct. The reaction is initiated by heating the mixture of reactants to a high temperature, typically around 3000°C, using a suitable ignition source.

Application: It is also used in the welding industry for joining metal parts and in the pyrotechnic industry for producing various types of fireworks.

Question 7

Rusting is an electrochemical process.

Answer

Rusting is an electrochemical process that involves the oxidation of iron in the presence of water and oxygen. The iron metal loses electrons to oxygen and forms iron oxide or rust, which weakens the structure of the metal. The process involves the transfer of electrons from one substance to another, which is the definition of an electrochemical process.

Question 8

Presence of chloride ions (Cl) enhances rusting. How rusting can be protected by magnesium? 

Answer

Rusting can be protected by magnesium through a process called cathodic protection. Magnesium metal, which is more reactive than iron, is connected to the iron structure and acts as a sacrificial anode. The magnesium metal corrodes instead of the iron, providing cathodic protection to the iron.

Question 9

Write some measures to prevent rusting. 

Answer

Here are some measures to prevent rusting:

  1. Coating: Coating the metal surface with a protective layer, such as paint, enamel, or varnish, can prevent rusting by isolating the metal surface from the atmosphere.
  2. Galvanization: Zinc coating or galvanization can be used to protect iron or steel surfaces from rusting. Zinc is more reactive than iron, so it corrodes first, protecting the underlying iron.
  3. Alloying: Adding small amounts of other metals, such as chromium or nickel, to iron or steel can improve its resistance to rusting.
  4. Oil or grease: Applying a thin layer of oil or grease to the metal surface can prevent the metal from coming into contact with water or air, preventing rusting.

Question 10

Write in brief the corrosion of Al, Zn and Cu in the presence of acidic foods and health hazards.

Answer

Aluminium, zinc, and copper can undergo corrosion in the presence of acidic foods.

  • Aluminium: Corrosion of aluminium in acidic foods can result in the formation of aluminium ions, which can cause food to discolour and develop an off taste. Prolonged ingestion of aluminium ions can lead to health problems such as Alzheimer’s disease, bone disorders, and kidney problems.
  • Zinc: Zinc can corrode in acidic foods, causing it to dissolve and contaminate the food. Ingesting large amounts of zinc can lead to health problems such as stomach cramps, nausea, and vomiting.
  • Copper: Copper can corrode in acidic foods, resulting in the formation of copper ions, which can contaminate the food and cause it to develop an off taste. Ingesting large amounts of copper can lead to health problems such as nausea, vomiting, and diarrhoea.

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