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Class 10 Science Chapter 3 Extra Questions and Answers Metals and Non-metals
Extra Questions for Class 10 Science Chapter 3 Metals and Non-metals with Answers Solutions
Metals and Non-metals Extra Questions Very Short Answer Type
Why are metals good conductors of electricity ?
Metals are good conductors of electricity because they contain free electrons. These free electrons move easily through the metal and conduct electric current.
Which property of graphite is utilised in making electrodes?
Graphite is a good conductor of electricity. Due to this property, graphite is utilised in making electrodes.
Which of the following metals will melt at body temperature ?
Gallium, Magnesium, Caesium, Aluminium
Gallium and caesium will melt at 37°C (body temperature).
Name two metals that do not react with water at all.
Lead and copper.
What happens when calcium is treated with water ?
Calcium reacts less violently with water and bubbles of hydrogen gas stick to its surface.
Generally, non-metals are not lustrous. Name a non-metal which is lustrous.
Explain any one reducing property of So, by giving chemical equation.
SO2 + H20 → H2SO4
What is the nature of metal oxides?
Metal oxides are basic in nature.
Why does calcium float in water ?
When calcium reacts with water, hydrogen gas is produced wich sticks to the surface of calcium, so it floats in water.
What is flux ?
Flux is a substance which is added to the ore, during reduction, for removing the non fusible impurities.
Why do copper objects develop a green coating in air?
Copper reacts with moist carbon dioxide in the air and gains a green coating of basic copper carbonate.
By explaining molleability and ductility, write that these are the properties of which type of elements.
(i) Malleable: A substance or material which can be beaten into thin sheets is called malleable.
Ex. Metals like Ag, Au etc.
(ii) Ductile: A substance capable of being drawn into thin wires is called ductile.
Ex. Ag, Au etc..
Which oxide of iron could be obtained on prolonged reaction of iron with steam?
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
In nature, metal A is found in a free state while metal B is found in the form of its compounds. Which of these two will be nearer to the top of the activity series of metals?
Metal B will be nearer to the top of the activity series of metals as it so reactive that it is found in combined state.
Arrange the following metals in decreasing order of their reactivity:
Fe, Zn, Na, Cu, Ag
Na > Zn > Fe > Cu > Ag.
Give an example of a sulphide ore which is reduced to metal by heating alone, i.e., by roasting.
How would you obtain mercury (Hg) from one of its ores? Give chemical relations only..
Cinnabar (HgS) on roasting is first changed to mercuric oxide which on further heating is reduced to mercury.
Metals are refined by using different methods. Name two metals refined by electrolytic refining.
Copper and gold.
What is rust?
The coating of brown, flaky substance on the surface of iron when it is kept exposed in moist air is called rust.
Explain rusting by citing an example and write a safety measure from rusting.
Corrosion : It is the show process of eating a way of metals by the reaction of atmo spheric air and moisture, e.g., rusting of iron, tarnishing of silver, formation of green coating over copper etc.
Prevention of corrosion : Rusting of iron is prevented by galvanising, by making alloys, painting, greasing or oiling, tin-plating.
What is aqua regia ?
It is freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1. It can dissolve gold. It is a highly corrosive liquid.
Which metals are mixed with iron to get stainless steel?
Nickel and chromium.
Why is stainless steel preferred for making household utensils?.
Stainless steel is preferred as it is non-reactive and so the milk or food is not spoiled in it.
When H2 SO, reacts with zinc, hydrogen gas is released but this reaction does not takes place with silver. Explain reason and also write chemical reactions.
Position of zinc in electrochemical series is above hydrogen, thus it is more reactive than hydrogen and can displace hydrogen from sulphuric acid, whereas silver is placed below hydrogen, i.e., less reactive than hydrogen and hence no reaction takes place.
Zn + H2SO4 → ZnSO4 + H2 ↑
Ag + H2SO4 → No reaction
On the basis of electrochemical series, explain that copper does not release hydrogen gas when it reacts with dilute sulphuric acid.
Position of copper in the electrochemical series is below hydrogen, thus it is less reactive than hydrogen and therefore is not capable to displace hydrogen from dilute acids like H2SO, hence reaction is not possible
Cu + H2SO4 → No reaction
What are ores and minerals ? Write the name and formula of two important ores of copper ?
Ores : Ores natural minerals which have sufficient quantity of metal present in it and from which metal can be extracted conveniently and economically are called ores.
Main Ores of Copper
(i) Sulphide Ore : Copper glance (Cu2S), Copper pytite (CuFes2)
(ii) Oxide Ore: Cuprite (Cu2O)
Minerals : The elements or compounds which occur naturally in the earth crust are known as minerals.
Metals and Non-metals Extra Questions Short Answer Type
Explain why the surface of some metals acquires a dull appearance when exposed to air for a long time.
The surface of some metals acquires a dull appearance when exposed to air for a long time due to the formation of a thin layer of oxide, carbonate or sulphide on their surface by the slow action of the various gases present in air.
Give two examples each of the metals that are good conductors and poor conductors of heat respectively.
(a) Good conductors: Ag and Cu
(b) Poor conductors: Pb and Hg
Name one metal and one metal that exist in liquid state at room temperature. Also name two metals having melting point less than 310 K (37°C).
Metal: Mercury (Hg)
Non-metal: Bromine (Br)
Two metals with melting points less than 310K are Cesium (Cs) and Gallium (Ga).
The following reaction takes place when aluminium powder is heated with MnO2
3MnO2(s) + 4Al(s) → 3Mn(l) + 2Al2O2 (l) + Heat
(a) Is aluminium getting reduced ?
(b) Is MnO, getting oxidised ?
(a) No, because oxygen is added to aluminium therefore, it is getting oxidised.
(b) No, since manganese has lost oxygen therefore, it is getting reduced.
A solution of CuSO4 was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.
Iron is more reactive than copper. Hence, when a solution of CuSo4 is kept in an iron pot, iron slowly displaces copper from the solution and blue colour of the solution keeps fading away. Because of iron going into solution as iron sulphate, a number of holes are seen in the iron pot. The reaction is
CuSO4(aq) + Fe(s) → FeSO4(aq) + Cu(s)
Generally, when metals are treated with minerals acids, hydrogen gas is liberated but when metals (except Mn and Mg) are treated with HNO3, hydrogen is not liberated, why?
It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to H2O and itself get reduced to any of the oxides of the nitrogen, like NO2 NO, etc.
Metals replace hydrogen from dilute acids, whereas non-metals do not. Why?
Answer: Hydrogen from dilute acids can only be replaced if electrons are supplied to H+ ions of the acid.
H2SO4 (aq) → 2H+ (aq) + SO 2- (aq)
2H+ + 2e– → H2 (g)
HCl (aq) + H+ → (aq) + Cl–(aq)
H+ + e– → H
2H → H2 (g)
Metals have a tendency to lose electrons and hence they supply electrons, i.e., they are electron donors. That is why metals displace hydrogen from dilute acids.
On the other hand, non-metal is an electron acceptor. It cannot supply electrons to H+ and hence, it does not displace hydrogen from dilute acids.
A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify M and black coloured product and also explain the reaction of M with oxygen.
M is copper. It reacts with oxygen to form Slack coloured compound, CuO.
2Cu + O2 → 2CuO (Black)
What happens when :
(i) iron nail is placed in silver nitrate solution ?
(ii) iron strip is dipped in zinc sulphate solution?
(i) Iron is more reactive than silver.
Fe (s) + 2AgNO3(aq) → Fe(NO3)2(aq) + 2Ag(s)
(ii) Iron is below zinc in the reactivity series; therefore, iron cannot displace zinc from zinc sulphate solution. No reaction takes place.
Why do metals not evolve hydrogen gas with nitric acid ?
When metal reacts with nitric acid (HNO3), hydrogen gas is not evolved. This is because HNO3 is a strong oxidising agent. It oxidises H2 produced to water and is itself reduced to any of the oxides of nitrogen (N2O, NO or NO2). For example,
3Cu(s) + 8HNO, (aq) – 3Cu(NO3)(aq) + 2NO(g) +4H2O (l)
(i) Name a metal for each case :
(a) It does not react with cold as well as hot water but reacts with steam.
(b) It dos not react with any physical state of water.
(ii) When calcium metal is added to water the gas evolved does not catch fire but the same gas evolved on adding sodium metal to water catches fire. Why is it so ?
(i) (a) Aluminium,
(ii) In both cases, the gas evolved is H2 When calcium reacts with water the heat evolved is not. sufficient for hydrogen to catch fire. On the other hand, sodium metal reacts with water violently and in this case a lot of heat is evolved which is sufficient for hydrogen to catch fire.
Which of the following reactions will not occur? Give reasons.
(i) MgSO4 (aq) + Fe(s)→ FeSO4(aq) + Mg(s)
(ii) MgSO4 (aq) + Cu(s) → CuSo4(aq) + Mg(s)
(iii) CuSO4 (aq) + Fe(s)→ FeSO4 (aq) + Cu(s)
(i) will not occur because Fe is less reactive than Mg. Reaction
(ii) will not occur because Cu is less reactive than Mg.
An ore gives carbon dioxide on treatment with a dilute acid. What steps will you take to convert such a concentrated ore into free metal ?
A metal carbonate reacts with a dilute acid to form carbon dioxide. Therefore, this ore is a carbonate ore. Carbonate ore is converted into free metal in the following two steps :
(i) Calcination : The carbonate ore is strongly heated in the absence of air to get the metal oxide.
(ii) Reduction : The metal oxideis reduced with carbon to get free metal.
What happens when :
(a) ZnCo3 is heated in the absence of oxygen ?
(b) a mixture of Cu2O and Cu2S is heated ?
(a) It undergoes calcination. The chemical reaction can be given as :
Give the reaction involved during extraction of zinc from its ore by:
(a) roasting of zinc ore
(b) calcination of zinc ore.
What is a thermit reaction State one use of this reaction.
The reaction between iron (III) oxide (Fe2O3) and aluminium gives out lots of heat. It is called the thermit reaction.
Iron (III) oxide Aluminium Iron Aluminium oxide This displacement reaction is used to join railway tracks or cracked machine parts.
The heat given out in the reaction melts the iron formed. The molten iron runs down between the tracks and welds them together.
Why shoul the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
It is easier to obtain metal from its oxide, as compared from its sulphides and carbonates. So prior to reduction, sulphide ores are converted into oxides by roasting and carbonate ores by calcination.
What is 24-carat gold ? How will you convert it into 18-carat gold ?
24-carat gold is pure gold. Pure gold is very soft and not suitable for making jewellery. Therefore, to increase its hardness, it is alloyed either with copper or silver.
18-carat gold is prepared by alloying 18 parts pure gold with 6 parts of either copper or silver.
What would happen to iron railings on the road side if they are not painted ? Why does it happen so ?
If the iron railing on the road side is not painted, a brown rust would form on its surface because the moist air of the atmosphere racts with iron to form brown flaky substance on its surface. The rust is hydrated iron (III) oxide, Fe2O3x.H2O.
Explain why, the galvanised iron article is protected against rusting even if the zinc layer is broken.
The galvanised iron article is protected against rusting even if the zinc layer is broken because zinc is more easily oxidised than iron. So when zinc layer on the surface of galvanised iron article is broken, then zinc continues to corrode but iron article does not corrode or rust.
Why is aluminium oxide considered an amphteric oxide ?
Aluminium oxide (Al2O3) shows basic as well as acidic behaviour because it reacts with
Whard is prepos hardnesd. Pure will you both acids and bases. Thus, it is considered an amphoteric oxide. The two types of reactions given by Al2O2 are as follows:
In this reaction, Al2O3 behaves as an acidic oxide because it reacts with a base to form salt and water.
Why are food cans tin-plated instead of zinc plated though zinc is cheaper than tin ?
Tin is less reactive than zinc. It is less likely to dissolve in the liquid stored in the food cAnswer: Tin reacts only with powerful acids whereas zinc can easily react even with tomatoes, so it is not safe to store food in zinc-plated cans.
When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.
Sodium (Na) and potassium (K) react with cold water to form basic salt NaOH and KOH respectively. The molecular mass of NaOH is 40. So, X is Na and Y is NaOH. The gas liberated during the reaction iş hydrogen (H2). So Z is H2.
2Na + 2H2O → 2NaOH + H2 + Heat energy .
An element A burns with golden flame in air. It reacts with another element B, atomic number 17 to give a product C. An aqueous solution of product Con electrolysis gives a compound D and liberates hydrogen. Identify A, B, C and D. Also write down the equations for the reactions involved.
A – Na; B – Cl2; C – NaCl; D – NaOH
2Na + Cl2 → 2NaCl
2NaCl (aq) + 2H2O (l) → 2NaOH (aq) + Cl2(g) + H2 (g)
Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in reaction mixture. He made the same observations when this element was treated with hydrochloric acid. Suggest how can he identify the produced gas. Write chemical equations for both the reactions.
the element is a metal
M + 2NaOH → Na2MO2 + H2
M + 2HCl → MCl2 + H2
The produced gas can be identified by bringing a burning matchstick near the reaction vessel.. The gas burns with a pop sound. This confirms that the gas is H2.
Give reasons :
(a) Platinum, gold and silver are used to make jewellery
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
(a) Platinum, gold and silver are used to make jewellery because of their bright shiny surface and high resistance to corrosion. Also they have high malleability and ductility.
(b) Sodium, potassium and lithium are stored under oil to prevent their reaction with oxygen moisture and carbon dioxide of air so as to protect them as they are highly reactive metals.
(c) Aluminium metal forms a thin layer of aluminium oxide all over its surface under the action of moist air. This layer prevents the metal underneath from further corrosion. It is cheap, easily available, malleable and ductile. Therefore, it is used to make utensils for cooking.
Give the differences between electrolytic reduction and reduction with carbon.
What is meant by refining of metals ? Describe the electrolytic refining of copper with a neat labelled diagram.
In electrolytic refining process, the impure metal is made as anode and a thin strip of pure metal is made as cathode. A solution of the metal salt is made as an electrolyte. A solution of the metal salt is made as an electrolyte. On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte.
An equivalent amount of pure metal from the electrolyte is deposited on the cathode. The soluble impurities go into the solution, whereas, the insoluble impurities settle down at the bottom of the anode and are known as anode mud.
At anode : Cu → Cu2+ + 2e–
At cathode : Cu2+ + 2e– → Cu
An ore on heating in air produces sulphur dioxide. Which process would you suggest for its concentration ? Describe briefly any two steps involved in the conversion of this concentrated ore into related metal.
The ore on heating produces sulphur dioxide gas so it is sulphide ore. The method used for its concentration is “froth floatation process”. After concentration of the ore following two steps would be followed to convert it into metal.
(i) Roasting: The sulphide ore is converted into its oxide by heating it in the presence of air.
MS + O2 → MO + SO2 ↑
(ii) Reduction of metal oxide to metal : The oxide formed by roasting is then reduced to metal by using a suitable reducing agent like carbon (coke).
During extraction of metals, electrolytic refining is used to obtain pure metals.
(i) Which material will be used as anode and cathode for refining of silver metal by this process ?
(ii) Suggest a suitable electrolyte also.
(iii) In this electrolytic cell, where do we get pure silver after passing electric current ?
(i) Anode : Impure silver
Cathode : Pure silver
(ii) Electrolyte : Silver salt, such as AgNO3, AgCl, etc.
(iii) We get pure silver at cathode.
A metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved.
Metals low in activity series can be obtained by reducing their sulphides or oxides by heating. Mercury is the only metal that exists as liquid at room temperature. It can be obtained by heating cinnabar (HgS), the sulphide ore of mercury.
The reactions are as follows:
How is copper obtained from sulphide ore? Give equation of the reactions.
(i) Sulphide ore of copper i.e., Cu2S is concentrated by froth floatation process.
(ii) Ore is then roasted.
(iv) Electrolytic refining of Blister copper is done to obtain pure copper.
How can a layer of aluminium oxide on an aluminium object be made thicker ? What is this process called ?
Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes resistance to further corrosion. The resistance can be improved further by making the oxide layer thicker. This process is called anodising.
During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can be dyed easily to give aluminium articles an attractive finish.
(i) A metal M is found in nature as MCO3. It is used in galvanising iron articles. Name the metal.
(ii) How can the metal be obtained from its carbonate ore ?
(i) The metal is zinc (Zn).
(ii) The carbonate ore is first heated strongly in limited supply of oxygen and changed into its oxide. This process is called calcination.
In the formation of the compound XY, atoms of X lost one electron each while atoms of Y gained one electron each. What is the nature of bond in XY? Predict the two properties of XY.
The atoms of X lose electrons whereas the atoms of Y gain electrons. Thus, there is transfer of electrons from atoms of X to atoms of Y. The bond formed by the transfer of electrons is called ionic bond. Therefore, the nature of bond in the compound XY is ionic.
Properties of ionic compound XY:
- The compound will be soluble in water.
- The compound will conduct electricity when dissolved in water or in molten state.
Explain how the properties of any allow are different from those of constituent metals.
- Alloys are stronger and harder than the constituent metals.
- Alloys are more resistant to corrosion.
- Alloys have lower melting point than the constituent metals.
- Alloys have lower electrical conductivity than pure metals.
State reason for the following:
(i) Lemon is used for restoring the shine of tarnished copper vessels.
(ii) A metal sulphide is converted into its oxide to extract the metal from the sulphide ore. .
(iii) Copper wires are used in electrical connections.
(i) When copper vessels are exposed to moist air, they form a green coating of basic copper carbonate (CuCO3.Cu(OH)2].
The sour substances such as lemon or tamarind juice contain acids. Lemon juice contains citric acid and tamarind contains tartaric acid. These acids dissolve the coating of copper oxide or basic copper carbonate present on the surface of tarnished copper vessels and make them shining red-brown again.
(ii) It is easier to obtain a metal from its oxides as compared to its sulphides and carbonates. So, prior to reduction, metal carbonate and sulphides must be converted into metal oxides. A carbonate ore is converted into oxide by calcination whereas a sulphide ore is converted into oxide by roasting.
(iii) Copper wires are good conductor of electricity, so, they are used in electrical connections.
Describe the extraction of metal from the sulphide ore of zinc by giving chemical equation.
(i) Roasting :
(ii) Reducton of oxide are:
Metals and Non-metals Extra Questions Long Answer Type
What are ionic or electrovalent compounds ? Give an example of ionic compound. Explain with reason four properties of these compounds.
Ionic compounds are those compounds which are formed by the transfer of electrons from a metal to a non-metal. For example, NaCl.
- Physical nature : Ionic compounds are hard and solid due to strong force of attraction between oppositely charged ions.
- Melting point and boiling point : As more amount of energy is required to break strong bonds. So, they have high melting point and boiling point.
- Solubility: These are soluble in water (polar solvent) but insoluble in organic solvent.
- Conduction of electricity: They conduct electricity in solution or molten state as ions move towards opposite electrodes.
Two ores A and B were taken. On heating ore A gives Co2 whereas, ore B gives SO2 What steps will you take to convert them into metals ?
Since ore A gives CO2 and ore B gives SO2. Therefore, ores are MCO3 and MS.
As A is a carbonate ore, it is first subject to calcination followed by reduction.
Write the names and symbols of two most reactive metals. Explain by drawing electronic structure how any one of them reacts with a halogen. Explain any two physical properties of the compound formed.
Most reactive metals are Na (sodium) and K (potassium)
Na → Na+ + e–
Cl + e– → Cl–
Physical properties :
(i) Physical nature : Hard and solid due to strong attractive forces between oppositely charged ions.
(ii) High melting point and boiling point because more amount of energy is required to break strong force of attraction.
(i) Hydrogen is not a metal but it has been assigned a place in the reactivity series of metals. Explain.
(ii) How would you show that silver is chemically less reactive than copper?
(i) Though hydrogen is not a metal but even then it has been assigned a place in the activity series. The reason is that like metals, hydrogen also has a tendency to lose electron and forms a positive ion H+.
The metals which lose electrons less readily than hydrogen are placed below it and the metals which lose electrons more readily than hydrogen are placed above it in the reactivity series of metals.
(ii) By displacement reaction silver can be shown to be chemically less reactive than copper or copper is more reactive than silver. If a pice of silver is immersed in a solution of copper sulphate, no reaction will take place because silver is less reactive than copper and will not displace copper from the copper sulphate solution.
CuSO4 (aq) + Ag(s) → No reaction
On the other hand, if a copper plate is placed in a solution of silver nitrate, copper will slowly displace silver from the solution and blue solution of copper nitrate is formed.
This shows the copper is more reactive than silver.
(i) What is an ionic bond ?
(ii) How is an ionic bond formed ?
(iii) Write the formation of magnesium chloride.
(i) The chemical bond formed by the transfer of electrons from one atom to another is known as an ionic bond.
(ii) An ionic bond is formed when one of the atoms can donate electrons to achieve the inert gas electronic configuration and other atom needs electrons to achieve the inert gas electronic configuration.
When a metal (usually 1, 2 or 3 electrons in outermost shell) reacts with a non-metal (usually 5, 6 or 7 electrons in outermost shell), transfer of electrons takes place from metal atoms to the non-metal atoms and an ionic bond is formed. There is a strong force of electrostatic attraction between metallic cation and non-metallic anion which is responsible for the formation of ionic bond.
(iii) Formation of magnesium chloride (MgCl2) : The atomic number of magnesium is 12. It has two electrons in its valence shell as shown below :
12Mg – 2, 8, 2,
Magnesium, therefore, has a tendency to lose the 2 valence electrons and in the process attains the electronic configuration of neon.
Chlorine (atomic number 17) has 7 electrons in the valence shell. It has a tendency to gain one electron to complete its octet.
Thus, when magnesium and chlorine are brought together, the magnesium atom transfers its two valence electrons to two chlorine atoms. In the process, both the atoms acquire the stable electronic configuration of nearest inert gases. The positively charged magnesium ion Mg2+ and negatively charged chloride ions (Cl–) are now held together by the electrostatic force of attraction and form ionic bond.
Mg2+ + 2Cl– → Mg2+ 2Cl– Or MgCl2
This process can also be shown as below :
(i) Distinguish between ionic and covalent compounds under the following properties :
(a) Strength of forces between constituent elements.
(b) Solubility of compounds in water.
(c) Electrical conduction in substances.
(ii) Explain how the following metals are obtained from their compounds by the reduction process :
(a) Metal M which is in the middle of the reactivity series.
(b) Metal N which is high up in the reactivity series. Give one example of each type.
(i) (a) Ionic compounds have strong force of attraction between the oppositely charged ions (e.g., Na+ and Cl–), so they are solids. Covalent compounds have weak force of attraction between their molecules, so they are usually liquids or gases.
(b) Ionic compounds are soluble in water but covalent compounds are insoluble in water. 1.
(c) Ionic compounds conduct electricity when dissolved in water or when melted because they contain ions (charged particles). But, covalent compounds like glucose do not conduct electricity because they do not contain ions.
(ii) (a) The metal M which is in the middle of the reactivity series (such as iron, zinc, lead, copper, etc.) is moderately reactive. So, for obtaining such metals from their compounds, their sulphides and carbonates (in which they are present in nature) are first converted into their oxides by the process of roasting and calcination respectively.
The metal oxides (MO) are then reduced to the corresponding metals by using suitable reducing agents such as carbon. For example, zinc metal from its oxide is obtained as follows:
(b) The metal N which is high up in the reactivity series (such as sodium, magnesium, calcium, aluminium, etc.), very reactive and cannot be obtained from its compound by heating with carbon.
Therefore, such metals are obtained by electrolytic reduction of their molten salt. For example, sodium is obtained by the electrolysis of molten sodium chloride (NaCl).
At cathode : Na+ + e– → Na
At anode: 2Cl– → Cl2 + 2e–
(i) Distinguish between ‘roasting’ and ‘calcination’. Which of these two is used for sulphide ores and why?
(ii) Write a chemical equation to illustrate the use of aluminium for joining cracked railway lines.
(iii) Name the anode, the cathode and the electrolyte used in the electrolytic refining of impure copper.
(i) Roasting: It is the process in which sulphide ores of the metals are converted into oxides by heating them in the presence of excess air. For example, zinc sulphide is converted into zinc oxide by roasting.
Calcination : It is the process in which carbonate ores of the metals are decomposed into oxides by heating them in the absence or limited air. For example, zinc carbonate decomposed into zinc oxide and carbon dioxide by calcination.
Out of roasting and calcination, only roasting is used for sulphide ores. This is because it is easier to obtain metal from its oxide as compared to its sulphide.
(iii) Anode – Impure copper
Cathode – Strip of pure copper
Electrolyte – Acidified copper sulphate solution.
Write about different chemical processes used for obtaining a metal from its oxides, for metals low in the reactivity series, metals in the middle of reactivity series and metals towards the top of the reactivity series.
For obtaining the metals that are low in the reactivity series, oxides of such metals can be reduced to metals by simply heating them in the air.
For example, HgS or cinnabar is the ore of mercury metal which on heating changes to Hgo. This metal oxide (HgO) gets reduced to mercury metal (Hg) on further heating.
(ii) For obtaining metals that are in the middle of reactivity series, oxides of such metals can be reduced with coke (carbon) which acts as a reducing agent.
For example, iron (III) oxide can be reduced to iron, as follows :
(iii) For obtaining metals that are high up in the reactivity series, their oxides are reduced to metals by electrolysis.
At anode : At anode :
6(O)2- – 3O2 + 12e–
Give reasons : :
(i) Reactivity of Al decreases if it is dipped in HNO3.
(ii) Carbon cannot reduce the oxides of Na or Mg.
(iii) NaCl is not a conductor of electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state.
(iv) Iron articles are galvanised.
(v) Metals like Na, K, Ca and Mg are never found in their free state in nature.
(i) Due to the formation of a layer of oxide, i.e., Al2O3 it becomes less reactive.
(ii) Na or Mg are more reactive metals as compared to carbon. So, their oxides are more stable.
(iii) In solid NaCl, the movement of ions is not possible due to its rigid structure but in aqueous solution or molten state, the ions can move freely. These free ions are responsible for conduction of electricity.
(iv) Iron articles are galvanised to protect them from corrosion.
(v) Na, K, Ca and Mg are highly reactive metals and thus never found in their free state in nature.
Write balanced equation of the following reactions :
(i) Dilute sulphuric acid reacts with granular zinc.
(ii) Dilute hydrochloric acid reacts with aluminium powder.
(i) H2SO4 + Zn → ZnSO4 + H2 ↑
(ii) 2Al + 6HCl(aq) → 2AlCl3 + 3H2 ↑