Metallurgy Solutions for Class 10 Science ICSE Board (Concise - Selina Publishers)

Exercise 7A

1. (a) Name the three classes in which elements are classified. Which was the first metal used by man?

Ans: Elements are classified into metals, nonmetals and metalloids. First metal used by man was copper.

(b) Name the metal and non-metal present in abundance in the earth crust.

Ans: Metal - Aluminium, Non-Metal - Oxygen

2. Name the metal which is a constituent of:

(a) Blood pigment

Ans: Iron (Fe)

(b) Plant pigment

Ans: Magnesium (Mg)

3. Give the importance of the following in living beings:

(a) Nitrogen

Ans: Nitrogen is used in preservation of food.

(b) Hydrogen

Ans: Hydrogen is used in the process of hydrogenation of vegetable oil.

(c) Carbon

Ans: Carbon is responsible for growth and development of living organisms.

4. State the position of the following in the periodic table:

(a) Alkali metals

Ans: IA

(b) Alkaline earth metal

Ans: IIA

(c) Halogens

Ans: VIIA

(d) Aluminium

Ans: IIIA

5. Name:

(a) A liquid non-metal

Ans: Bromine 

(b) Two metalloids

Ans: Boron and Silicon

(c) Metal which does not corrode easily.

Ans: Aluminium

(d) Two metals which react with cold water.

Ans: Sodium and potassium

(e) A non-metal which can form a positive ion,

Ans: Hydrogen 

(f) A non-metal which shows reducing property.

Ans: Carbon 

6. From the list of characteristics given below, select the five which are relevant to non-metals and their compounds:

A. Ductile

B. Conduct electricity

C. Brittle

D. Acidic Oxides

E. Basic Oxides

F. Discharged at anode

G. Discharged at cathode

H. Ionic chlorides

I. Covalent chlorides

J. Reaction with dilute sulphuric acid yields hydrogen

K. 1,2 or 3 valence electrons

L. 5,6 ,7 valence electrons

(Write the five letters corresponding to the correct characteristics).

Ans: Acidic oxide(D)

Discharged at anode (F)

Covalent chlorides (I)

5,6,7 valence electrons (L)

Brittle(C)

7. (a) Why are alkali metals kept in kerosene oil?

Ans: Alkali metals have a tendency to react with moisture and air, so they are kept in kerosene oil.

(b) Why is hydrogen kept in the metal activity series?

Ans: Hydrogen forms the positive ion (cation) by losing one electron, so hydrogen is kept in a metal activity series.

(c) Why do gold ornaments look new even after several years of use?

Ans: Gold being less reactive kept lowest in the reactivity series. So being a noble element gold will not react with other elements due to which gold ornaments look new after several years of use.

8. From the metals copper, iron, magnesium, sodium and zinc, select a different metal in each case which

a. does not react with dilute hydrochloric acid

Ans: Copper 

b. can form 2+ and 3+ ions

Ans: Iron(Fe)

c. Arrange the above metals in the decreasing order of reactivity.

Ans:   Na > Mg > Zn > Fe > Cu

9. Which metal occurs as:

(a) A sulphide

Ans: Lead

(b) A halide

Ans: Silver 

(c) A carbonate

Ans: Zinc 

(d) An oxide

Ans: Iron 

10. Distinguish between:

(a) A mineral and an ore

Ans: 

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

(b) An ore and a metallic compound

Ans: 

11. Which metal can be extracted from each one of the following ores:

(a) Bauxite

Ans: Aluminium

(b) Calamine

Ans: Zinc

(c) Haematite

Ans: Iron 

12. Explain the following terms:

(a) Ore

Ans: Ores are minerals from which metals can be commercially extracted at a relatively low cost and with less amount of effort.

(b) Gangue

Ans: The earthy impurities associated with the ore, such as silica, mud, and so on, are referred to as gangue.

Exercise 7B

1. Give the principles of:

(a) Hydraulic washing

Ans: The fundamental criterion is the difference in densities between both the ore and the gangue.

(b) Froth floatation

Ans: This technique is based on the ore's preferential wettability with oil and the gangue particles' preferential wettability with water.

(c) Electromagnetic separation

Ans: Magnetic properties 

2. (a) Name the methods by which concentrated ore is converted to metallic oxide.

Ans:  Roasting and calcination 

(b) State three objectives achieved during the roasting of ores.

Ans: 

(i) It removes moisture from the ore.

(ii) It expels oxide.

(iii) It oxidises sulphide ores to oxide ores.

3. Name:

(a) The processes involved in

(i) Concentration

Ans:

1. Hydrolytic method

2. Magnetic Separation

3. Froth floatation

4. Leaching

(ii) Refining of ores

Ans: 1. Distillation

2. Liquation

3. Oxidation

4. Electro- refining

(b) Two metallic oxides which cannot be reduced by carbon, carbon monoxide or hydrogen.

Ans: Sodium and Potassium 

4. Why does iron or zinc not occur free in nature?

Ans: Iron and zinc are very reactive elements and so they do not exist in free state. They are found in the form of oxides, carbonates and sulphides. 

5. What do you observe when hydrogen is passed over heated copper oxide?

Ans: Black copper oxide is reduced to brown/red.

\[CuO + H_{2} \rightarrow Cu + H_{2}O\]

6. Compare roasting and calcination.

Ans: 

7. (a)Name an ore of Zinc.

Ans: ZnS

(b)Which process is applied to concentrate it?

Ans: Froth floatation is used to concentrate it.

(c) How is concentrated ore changed to oxide?

Ans: Concentrated ore is changed into oxide by heating ZnS in excess of air.

\[2ZnS + 3O_{2} \rightarrow 2ZnO + 2SO_{2}\]

8. a. Some metallic oxides can be reduced by hydrogen, carbon and carbon monoxide and some cannot. Explain.

Ans: Because the oxides of highly active metals such as potassium, sodium, calcium, magnesium, and aluminium have a strong affinity for oxygen, they cannot be reduced by carbon, carbon monoxide, or hydrogen.

The middle activity series metals (iron, zinc, lead, and copper) are highly reactive and do not exist in oxide form. In nature, they are found as sulphides or carbonates. These are first transformed to oxides, and then C, CO, or H2 can be used to reduce them.

\[ZnO+C \rightarrow Zn+CO\]

\[PbO+CO \rightarrow Pb+CO_{2}\]

Metals at lowest position are less reactive, and their oxides can be converted to metals simply by heating.

b. Write a balanced equation for the reduction of copper (II) oxide by hydrogen. 

Ans: \[ CuO + H_{2} \rightarrow Cu + H_{2}O \]

9. How are the following metallic oxides reduced? Write equations:

(a) Iron(II) oxide

Ans:

\[ 4FeO + O_{2} \rightarrow 2Fe_{2}O_{3} \]

\[ Fe_{2}O_{3} + 3CO \rightarrow 2Fe +3CO_{2} \]

(b) Zinc oxide

Ans: Zinc oxide is reduced by coke.

\[ ZnO + C \rightarrow Zn + CO \]

10. State why aluminium is extracted from its oxide by electrolysis while copper, lead, iron by reducing agents and mercury and silver by thermal decomposition.

Ans: Because of its strong affinity for oxygen, aluminium cannot be reduced by carbon or carbon monoxide. Electrolysis is used to separate it from its oxide.

Metals like copper, lead, and iron are in the centre of the activity series and are moderately reactive, allowing carbon, CO, and hydrogen to reduce their oxides.

Mercury and silver are less reactive and are placed lower in the reactivity series. The oxides of these metals are reduced to metals by heating their oxides.

11. An ore being heated in air forms sulphurous anhydride. Write the process used for the concentration of this ore.

Ans: Froth Floatation is used for the concentration of this ore. 

12. a. Define roasting. Name an ore on which roasting is done. Give balanced equation.

Ans: Roasting is the process of raising the temperature of concentrated ore in the presence of air. Zinc oxide is obtained by roasting the zinc blend ore.

Example: Oxidation of zinc sulphide to zinc oxide.

\[ 2ZnS + 3O_{2} \rightarrow 2ZnO + 2SO_{2} \]

b. Define calcination. Give an example and equation for calcination.

Ans: Calcination is the process of heating a concentrated ore like carbonate or hydrated oxide to a high temperature without using air.

For Example, Decomposition of metal carbonates to form metal oxides.

\[ ZnCO_{3} \rightarrow ZnO + CO_{2} \]

\[ CaCO_{3} \rightarrow CaO + CO_{2} \]

13. How are the metals like sodium, potassium and calcium obtained? Give equations.

Ans: Sodium, potassium and calcium metals are obtained by electrolytic reduction of fused metallic salts.

14. Give equation for the reduction of

(a) Copper oxide

Ans: 

CuO+C → Cu+CO

CuO+Cu → Cu+CO2

CuO+H2 → Cu+H2O

(b) Iron (III) oxide

Ans: 

\[ FeO+C \rightarrow Fe+CO \]

\[ FeO + CO \rightarrow Fe + CO_{2} \]

\[ FeO+ H_{2} \rightarrow Fe+H_{2} \]

(c) Lead (II) oxide

Ans: 

\[ PbO + C \rightarrow Pb + CO \]

\[ PbO + CO \rightarrow Pb + CO_{2} \]

\[ PbO + H_{2} \rightarrow Pb + H_{2}O \]

(d) Zinc oxide

Ans:

\[ ZnO + C \rightarrow + CO \]

15. (a) On which factors does purification of metals depend?

Ans:  The purification depends upon:

1. Nature of metal.

2. Nature of impurities present in the metal.

3. Purpose for which metal is to be used

(b) Name the methods used for purification?

Ans:  Methods used for purification are:

1. Distillation

2. Liquation

3. Oxidation

4. Electro-refining

(c) With labelled diagrams explain electro-refining of a particular metal.

Ans: 

16. Choose the correct option:

(a) The metal other than aluminium, which has a strong affinity for oxygen is:

(A) Copper

(B) Magnesium

(C) Silver

(D) Gold

Ans: (B) Magnesium

(b) A metallic oxide which cannot reduced by normal reducing agents:

(A) Zinc oxide

(B) Magnesium oxide

(C) Copper(II) oxide

(D) Iron(III) oxide

Ans: (A) Zinc oxide

17. Fill in the blanks:

(a) Usually …………. (sulphide/carbonate) ores are subjected to ……………. (calcination/roasting) which is done in the absence of air.

Ans:  Usually carbonate ores are subjected to calcination which is done in the absence of air.

(b) Zinc blend is converted to oxide by ……… (roasting /calcination) process.

Ans:  Zinc blend is converted to oxide by roasting process.

(c) Froth floatation process is generally used to concentrate ………… ores (sulphide/carbonate).

Ans:  Froth floatation process is generally used to concentrate sulphide ores.

Exercise 7C

1. State the position of aluminium in the periodic table.

Ans: Position in the Periodic Table: Period 3, Group IIIA(13)

2. (a) Give the chemical names and formulae of the main ores of (i) aluminium, (ii) iron and (iii) zinc.

Ans: (i) Ores of aluminium

(ii) Ores of iron

(b) Which impurities are present in bauxite?

Ans: Bauxite ore contains approximately 60% aluminium oxide. The rest being sand, ferric oxide and titanium oxide.

(c) What is red mud, how is it removed?

Ans: Red mud consists of ferric oxide, sand etc. left after bauxite dissolves in NaOH forming sodium aluminate and is removed by filtration.

3. In order to obtain 1 tonne of aluminium, the following inputs are required: 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide. Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite.

a. When bauxite is treated with sodium hydroxide solution, what happens to

i. the aluminium oxide

Ans: Aluminium oxide dissolves in sodium hydroxide to generate sodium meta aluminate, leaving insoluble impurities such as ferric oxide behind, which are filtered out.

\[ Al_{2}O_{3}.2H_{2}O + 2NaOH \rightarrow 2NaAlO_{2} + 3H_{2}O \]

\[ 2AI + N_{2} \rightarrow 2AIN \]

\[ 2AI + 3H_{2}O \rightarrow Al_{2} O_{3} + 3H_{2} \]

\[ 2Al + 6HCl \rightarrow 2AlCl_{3} +3H_{2} \]

\[ 2Al + 2NaOH+2H_{2}O \rightarrow 2NaAlO_{3} +3H_{2} \]

ii. the iron (III) oxide

Ans: It does not react

b. i. Name the process used for the purification of bauxite.

Ans:  Baeyer's process

ii. Write the equation for the action of heat on aluminium hydroxide.

Ans: \[ 2Al(OH)_{3} \rightarrow Al_{2}O_{3} +3H_{2}O \]

c. i. Write the formula of cryolite.

Ans: Formula of cryolite is

Na3AlF6

ii. Write down the word which correctly completes the following sentence. By dissolving aluminium oxide in cryolite a (conducting/non-conducting) solution is produced.

Ans:  By dissolving aluminium oxide in cryolite, a conducting solution is produced.

iii. Why is so much graphite required for the electrolytic process?

Ans: Thick graphite rods are used as the anode. The anode has to be replaced from time to time, as it gets oxidised by evolved oxygen.

iv. Write the equation for the reaction which takes place at the cathode.

Ans:  Reaction at the cathode:

\[ 4Al^{3+} + 12e^{-} \rightarrow 4Al \]

v. What is cathode made up of?

Ans: The cathode is made of carbon.

4. Aluminium is extracted from its chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction.

a. Write three balanced equations for the purification of bauxite.

Ans:  \[ Al_{2}O_{3} . 2H_{2}O+ 2NaOH \rightarrow NaALO_{2} + 3H_{2} \]

\[ NaAlO_{2} + 2H_{2}O \rightarrow NaOH + Al(OH)_{3} \]

\[2Al(OH)_{3} \rightarrow Al_{2}O_{3} + 3H_{2}O \]

b. Name a chemical used for dissolving aluminium oxide. In which state of subdivision is the chemical used?

Ans: Chemicals used for dissolving aluminium oxide: Fluorspar and cryolite Alumina 20%, cryolite 60%, fluorspar 20%.

c. Write an equation for the reaction which takes place at the anode during the extraction of aluminium by the electrolytic process.

Ans: At anode: \[ Al - 3e^{-} \rightarrow Al^{3+} \]

d. Mention one reason for the use of aluminium in thermite welding.

Ans:  Aluminium is a good reducing agent used for thermite welding.

5. a. A to F below relate to the source and extraction of either zinc or aluminium:

A. Bauxite

B. Coke

C. Cryolite

D. Froth floatation

E. Sodium hydroxide solution

F. Zinc blende

i. Write down the three letters each from the above list which are relevant to

1. Zinc

Ans:  Zinc blende, Froth flotation, Coke

2. Aluminium

Ans:  Cryolite, Bauxite, Sodium hydroxide solution

ii. Fill in the blanks using the most appropriate words from A to F.

1. The ore from which aluminium is extracted must first be treated with ………………. so that pure aluminium oxide can be obtained.

Ans: The ore from which aluminium is extracted must first be treated with Sodium hydroxide so that pure aluminium oxide can be obtained.

2. Pure aluminium oxide is dissolved in ….. to make a conducting solution.

Ans: Pure aluminium oxide is dissolved in cryolite to make a conducting solution.

iii. Write the formula of cryolite.

Ans: Na3AlF6.

6. Explain with reasons:

(a) In the electrolytic reduction of alumina, the graphite anode is gradually consumed.

Ans:  In the electrolytic reduction of alumina, the graphite (anode) is oxidized by oxygen to CO and further forms CO2, so it is consumed and has to be replaced from time to time.

Equation: \[ 2C + O_{2} \rightarrow 2CO \]

or

Why does the anode have to be replaced in this process?

Ans: The process of roasting provides oxygen to convert metallic sulphides into metallic oxide and SO2 which takes place when heated in excess of air.

Carbonate is converted into oxide by the loss of CO2 which takes place in the absence of air and when heated strongly.

(b) Roasting is carried out on sulphide ores and not on carbonates ores.

Ans: Roasting provides oxygen to metal sulphides, which is required to convert them to metallic oxide and SO2.

Carbonate is changed to oxide by CO2 loss, which occurs in the absence of air and when heated to a high temperature.

(c) Carbon can reduce lead oxide but not aluminium oxide.

Ans: Because aluminium has a strong affinity for oxygen, it cannot be reduced by carbon, carbon monoxide, or hydrogen, but lead oxide is easily reduced to metal lead by carbon.

\[ PbO+C \rightarrow Pb+CO \]

(d) Electrolytic reduction is done to obtain aluminium.

Ans: Because of its high affinity for oxygen, aluminium oxide is an extremely stable molecule. It is difficult to reduce with standard reducing agents like carbon or hydrogen. As a result, electrolytic reduction is used to produce aluminium.

(e) Why 'food containing iron salts' should not be cooked in aluminium utensils?

Ans: Because aluminium appears before iron in the metal activity sequence, it can displace iron from iron salts, hence food containing iron salts should not be cooked in aluminium utensils.

(f) A neutral gas other than oxygen is formed at the anode during electrolysis of fused alumina.

Ans: Carbon is used to make an anode, which is oxidised in the presence of oxygen to produce carbon monoxide, a neutral gas.

\[ 2C+O_{2} \rightarrow 2CO \]

(g) Why is powdered coke sprinkled on top of the electrolyte?

Ans: On top of the electrolyte, powdered coke is sprinkled. Radiative heat loss is reduced. It also prevents the anode from burning.

7. For each substance listed below, explain its significance in the extraction of aluminium:

a. Bauxite

Ans: Bauxite Aluminium is extracted from bauxite ore. It contains 60% \[Al_{2}O_{3}\]

b. Sodium hydroxide

Ans: The ore from which aluminium is extracted must first be treated with sodium hydroxide solution so that pure aluminium oxide can be obtained.

c. Cryolite

Ans:  Cryolite It lowers the fusion temperature and enhances conductivity.

d. Graphite

Ans: Graphite Thick graphite rods are used as the anode in electrolytic reduction.

8. Distinguish between electrolytic methods of reduction and refining.

Ans: 

9. Give three ways in which the metal zinc differs from the non-metal carbon. At least one of the differences must be a chemical difference.

Ans: The three ways in which metal zinc differs from the non-metal carbon is:

1. Zinc has a valency 2 and carbon has valency 4.

2. Zinc does not form hydride but carbon does (CH4).

3. Oxides of zinc are amphoteric (ZnO) whereas oxides of carbon are acidic (CO2) and neutral (CO).

10.  a. Aluminium is a more active metal than iron but suffers less corrosion. Why?

Ans: When aluminium is exposed to atmospheric air, it reacts with oxygen, forming an aluminium oxide coating (Al2O3) on the surface. Corrosion is prevented by a strong, tightly adherent coating of aluminium oxide.

b. Explain and give reasons why aluminium vessels should not be cleaned with powders containing alkalis.

Ans: Aluminium containers should not be cleaned using alkali-based powders because alkalis react with aluminium to form meta aluminate.

11. (a) During the concentration of bauxite ore, aluminium goes in ………. (soluble/insoluble) part because of its …………… (acidic/basic/amphoteric) nature.

Ans: During the concentration of bauxite ore, aluminium goes in the soluble part because of its amphoteric nature.

(b) In Hoope's process, pure aluminium is collected at the …………… (top/bottom) of the electrolytic cell.

Ans: In Hoope's process, pure aluminium is collected at the top of the electrolytic cell.

Exercise 7D

1. Explain the following:

(a) Zinc is used to cover iron so as to prevent rusting of iron. Why?

Ans: Zinc, being an electropositive metal, oxidises and preserves iron. Zinc also produces a protective layer of zinc oxide (ZnO) on iron. This coating is sticky and impermeable, and it prevents rusting on the iron metal beneath it.

(b) In construction work, why is the alloy of aluminium–duralumin used rather than pure aluminium?

Ans: The alloy of aluminium–duralumin is used instead of pure aluminium in construction because of the following reasons:

Duralumin is lighter and stronger than aluminium, although aluminium is light and weak.

Moisture has no effect on duralumin, however moisture has an effect on aluminium.

Duralumin is corrosion resistant, whereas aluminium is corrosive.

2. What is an alloy? How do properties of an alloy differ from its constituents?

Ans: A homogeneous mixture of two or more metals, or one or more metals with certain non-metallic components, is referred to as an alloy.

The properties of alloys are frequently dissimilar to those of their constituents.

Example:   Without a little proportion of copper, gold is too soft to be used.

Steel with a low molybdenum content is tougher and more resistant to wear.

Copper and tin are less sonorous than bell metal.

Alnico, an aluminium, nickel, and cobalt alloy, can lift 60 times its own weight.

Hardness, wear resistance, toughness, and other qualities are improved by the addition of these components.

3. Both Brass and bronze contain copper as major constituents. Name other elements in these alloys.

Ans: The other element in Brass is Zinc.

The other elements in Bronze are Tin and Zinc.

4. Name an alloy of:

(a) Aluminium used in aircraft construction.

Ans:  Duralumin

(b) Lead used in electrical wiring or electrical work in joining metals.

Ans: Solder

(c) Copper in electrical appliances or household vessels.

Ans: Brass

(d) Zinc used in naval ships.

Ans: Brass

5. What is amalgam? State its use with an example.

Ans: Amalgam is a mixture or alloy of mercury with a variety of metals or alloys such as sodium, zinc, gold, and silver, as well as various non-metals.

Dental amalgam is a mercury-silver tin alloy combination.

6. (a) State two properties of brass that render it more useful for some purposes than its components.

Ans: 

1. Brass is malleable and ductile.

2. Brass resists corrosion

(b) A metal which forms a liquid alloy at ordinary temperature.

Ans: Sodium

7. Name the constituents of:

(a) Duralumin

Ans: Aluminium (95%), copper (4%), magnesium (0.5%) and manganese (0.5%).

(b) Solder

Ans: Lead (50%) and tin (50%).

(c) Bronze

Ans: Copper (80%), tin (18%) and zinc (2%).

(d) Brass

Ans: 60–70% Cu and 40–30% Zn

8. Name the following:

(a) A metal which is liquid at room temperature.

Ans: Mercury 

(b) A metal which is always present in the amalgam.

Ans: Mercury 

(c) The process of heating an ore to a high temperature in the presence of air.

Ans: Roasting

(d) The compound formed by the reaction between calcium oxide and silica.

Ans: Slag

(e) A compound which is added to lower the fusion temperature of the electrolytic bath in the extraction of aluminium.

Ans: Cryolite 

(f) Name an allotrope of a non-metal that allows electricity to pass through it.

Ans: Graphite

9. a)Brass is an alloy of

(i) Copper and tin

(ii) Copper and zinc

(iii) Zinc and lead

(iv) Lead and tin

Ans: (ii) Copper and zinc

(b) Steel is an alloy of iron and:

(i) Nickel

(ii) Zinc

(iii) Carbon

(iv) Aluminium

Ans: (iii) Carbon

(c) The reason for using aluminium in the alloy duralumin is (2019)

(i) Aluminium is brittle.

(ii) Aluminium gives strength.

(iii) Aluminium brings lightness.

(iv) Aluminium lowers melting point.

Ans: (iii) Aluminium brings lightness.

10. Name the alloy used for the following purposes.

(a) Making electric circuits

Ans: Nichrome

(b) Making medals

Ans: Bronze 

(c) Making parts of watches

Ans: Brass

(d) Surgical instruments

Ans: Stainless steel

(e) Aircraft

Ans: Duralumin and magnalium

Miscellaneous Exercise

1. The following is an extract from 'Metals in the Service of man, Alexander and street/Pelican 1976'.

'Alumina (aluminium oxide) has a very high melting point of over 2000oC so that it cannot readily be liquefied. However, conversion of alumina to aluminium and oxygen, by electrolysis, can occur when it is dissolved in some other substance'.

(i) Which solution is used to react with bauxite as the first step in obtaining pure aluminium oxide?

Ans: Sodium hydroxide 

(ii) The aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide. Write the equation for the reaction.

Ans: \[ 2Al(OH)_{3} \rightarrow Al_{2}O_{3} + 3H_{2}O \]

(iii) Name the element which serves both as anode and cathode in the extraction of aluminium.

Ans: Graphite 

(iv) Write the equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.

Ans: \[ Al^{3+} + 3e^{-} \rightarrow Al \]

(v) Give the equation for the reaction which occurs at the anode when aluminium is purified by electrolysis.

Ans: \[ Al-3e^{-} \rightarrow Al^{3+} \]

2. The following is a sketch of an electrolytic cell used in the extraction of aluminium:

(i) What is the substance of which the electrodes A and B are made?

Ans:  A(cathode) is made of carbon and B(anode) is a thick graphite rod.

(ii) At which electrode (A or B) is the aluminium formed?

Ans: Aluminium is formed at electrode A.

(iii) What are the two aluminium compounds in the electrolyte C?

Ans: Electrolyte C is Na3AlF6, Al2O3.

(iv) Why is it necessary for electrode B to be continuously replaced?

Ans: It is important to replace electrode B as it is oxidised by the oxygen released.

3. State the property of the metal being utilised in the following:

Ans: 

4. a. Answer the following questions:

i. Name a metal which is found abundantly in the Earth's crust.

Ans: Aluminium 

ii. What is the difference between calcination and roasting?

Ans: 

 iii. Name the process used for the enrichment of sulphide ore.

Ans: Froth floatation process 

iv. Write the chemical formula of one main ore of iron and aluminium.

Ans: 

Ores of iron

Ores of aluminium

v. Write the constituents of the electrolyte for the extraction of aluminium.

Ans:  Constituents of the electrolyte for the extraction of aluminium are pure alumina (Al2O3), cryolite (Na3AlF6) and fluorspar (CaF2).

2012

a. Name the following metals:

i. A metal present in cryolite other than sodium.

Ans: Aluminium

ii. A metal which is unaffected by dilute or concentrated acids.

Ans: Aluminium

iii. A metal present in Period 3, Group 1 of the periodic table.

Ans: Sodium

b. The following questions are relevant to the extraction of aluminium:

i. State the reason for addition of caustic alkali to bauxite ore during purification of bauxite.

Ans: Caustic alkali is added to bauxite ore during extraction as the insoluble part of bauxite is removed and the alumina component is then precipitated.

ii. Give a balanced chemical equation for the above reaction.

Ans:  \[ Al_{2}O_{3}.2H_{2}O + 2NaOH \rightarrow 2NaAlO_{2} + 3H_{2}O \]

iii. Along with cryolite and alumina, another substance is added to the electrolyte mixture. Name the substance and give one reason for the addition.

Ans: Fluorspar is added along with cryolite and alumina as it helps the mixture to fuse at 950 oC instead of 2050 oC, also liquid aluminium is obtained at this temperature.

2013

a. 

Using the information above, complete the following:

i. ________ is the metallic element.

Ans: Y

ii. Metal atoms tend to have a maximum of _______ electrons in the outermost energy level.

Ans: 3

iii. Non-metallic elements tend to form _______ oxides, while metals tend to form ________ Oxides.

Ans: Acidic, Basic

iv. Non-metallic elements tend to be ________ conductors of heat and electricity.

Ans: Poor

v. Metals tend to ________ electrons and act as ________ agents in their reactions with elements and compounds.

Ans: Lose, Reducing

2014

a. The main ore used for the extraction of iron is

i. Haematite

ii. Calamine

iii. Bauxite

iv. Cryolite

Ans:  i. Haematite

b. Heating an ore in a limited supply of air or in the absence of air at a temperature just below its melting point is known as

i. Smelting

ii. Ore dressing

iii. Calcination

iv. Bessemerisation

Ans:  iii. Calcination

c. State the main components of the following alloys:

i. Brass

Ans: Copper and Zinc

ii. Duralumin

Ans: Aluminium, magnesium, copper and manganese

iii. Bronze

Ans: Copper, zinc and tin.

d. Name the following:

i. The property possessed by metals by which they can be beaten into sheets.

Ans: Malleability is the property possessed by metals by which they can be beaten into sheets.

ii. A compound added to lower the fusion temperature of an electrolytic bath in the extraction of aluminium.

Ans: Cryolite is used in the extraction of aluminium to lower the fusion temperature of an electrolytic bath.

iii. The ore of zinc containing its sulphide.

Ans: Zinc Blende 

2015

(a) Choose the most appropriate answer from the following list of oxides which fit the description. Each answer may be used only once:

(SO2, SiO2, Al2O3, MgO, CO, Na2O)

(i) A basic oxide.

Ans: Na2O

(ii) An oxide which dissolves in water forming an acid.

Ans: SO2

(iii) An amphoteric oxide.

Ans: Al2O3

(iv) Covalent oxide of a metalloid.

Ans: SiO2

(b) For each of the substances listed below, describe the role played in the extraction of aluminium.

(i) Cryolite

Ans: The fusion temperature is reduced from 2050°C to 950°C, and conductivity is improved.

(ii) Sodium hydroxide

Ans: Sodium hydroxide plays two roles in the extraction of aluminium.

To make sodium aluminate, finely ground bauxite (aluminium ore) is heated under pressure for 2-8 hours at 140 °C to 150 °C with conc. caustic soda solution (NaOH solution).

\[ Al_{2}O_{3}.2H_{2}O +\] \[2NaOH \rightarrow \] \[2Na AlO_{3}\] \[+\] \[3H_{2}O\]

Second, when sodium aluminate is diluted with water and cooled to 50°C, it is hydrolyzed, yielding aluminium hydroxide as a precipitate. Here, the impurities dissolve in sodium hydroxide.

(iii) Graphite 

Ans: In the fused electrolyte, thick graphite rods are suspended. They function as an anode, releasing oxygen gas.

2016

(i) Name the solution used to react with Bauxite as a first step in obtaining pure aluminium oxide, in the Baeyer's process.  

Ans: Concentrated caustic soda 

(ii) Write the equation for the reaction where the aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide.

Ans: 2Al(OH)3 \[ \leftrightarrow \] Al2O3+3H2O

(iii) Name the compound added to pure alumina to lower the fusion temperature during the electrolytic reduction of alumina.

Ans: Cryolite 

(iv) Write the equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.

Ans: At the cathode: Al3+ + 3e- → Al

(v) Explain why it is preferable to use a number of graphite electrodes as anode instead of a single electrode, during the above electrolysis.

Ans: The anode has to be replaced from time to time as it gets oxidised by oxygen evolved at the anode

Position and Characteristics of S Block Elements

Alkali essence and alkaline earth essence are planted in the s block of the periodic table. 

• In certain circumstances, these essences occur naturally as carbonates, sulfides, oxides, or halides in the earth’s crust and these are called minerals. They're veritably reactive and hence can not be plant free in nature. 

• Nature Soft, low boiling, and melting points, argentine-white in color, lustrous. 

• Relating Ionic in nature, forms electrovalent composites. Alkali essence forms positive ions (M) and alkaline earth essence forms bi positive ions (M2).