Q1. Why is potassium kept immersed in kerosene? [2021 C]
Ans. Potassium is kept immersed in kerosene because it reacts vigorously with air and water. The reaction with air forms a layer of potassium oxide on the surface, while the reaction with water produces potassium hydroxide. Both of these reactions release hydrogen gas, which is highly flammable. By keeping potassium immersed in kerosene, it is protected from air and water, preventing any unwanted reactions.
Q2. Give reason why:
(a) gold and silver are used for making jewellery.
(b) a few metals are used for making cooking utensils. [2021 C]
Ans. (a) Gold and silver are highly malleable metals so, they are used for making jewellery.
(b) Certain metals, such as stainless steel, copper, and aluminum, are used for making cooking utensils due to their specific properties. Stainless steel is chosen for its durability, resistance to corrosion, and ease of cleaning. Copper is an excellent conductor of heat, allowing for even distribution of heat during cooking. Aluminum is lightweight and has good thermal conductivity, making it suitable for cookware. These metals provide the necessary characteristics required for efficient and safe cooking.
Q3. Compare in tabular form the reactivities of the following metals with cold and hot water: 
Q4. (a) Write electron dot structure of Ca (At. No. 20) and O (At. No. 8).
(b) Show the formation of calcium oxide by transfer of electrons.
(c) Name the ions present in this compound.
(d) List four important characteristics of this compound. 
(b) The formation of calcium oxide (CaO) involves the transfer of electrons. Calcium (Ca) donates two electrons to oxygen (O) to form Ca2+ cation and O2- anion. The ionic bond is formed between these ions to create calcium oxide.
(c) In calcium oxide (CaO), the ions present are Ca2+ (calcium cation) and O2- (oxygen anion).
(d) Four important characteristics of calcium oxide (CaO) are:
Q5. List three differentiating features between the processes of galvanisation and alloying. 
Ans. Three differentiating features between the processes of galvanisation and alloying are as follows:
Q6. What would a student report nearly after 30 minutes of placing duly cleaned strips of aluminium, copper, iron and zinc in freshly prepared iron sulphate solution taken in four beakers? 
Ans. After approximately 30 minutes, the student would observe that the strip of iron would start to show signs of corrosion or rusting. This is because iron is more reactive than copper, aluminium, and zinc and will displace the iron from the iron sulphate solution, forming iron oxide (rust) on its surface.
Q7. A pale green solution of ferrous sulphate was taken in four separate test tubes marked I, II, III and IV. Pieces of Cu, Zn and Al were dropped in test tubes II, III and IV respectively. In which case(s)
(a) the colour of ferrous sulphate solution will match with the colour in test tube (I)? Give reason.
(b) the colour of ferrous sulphate solution will fade and black mass will be deposited on the surface of the metal? [2019 C]
Ans. (a) The colour of the ferrous sulphate solution in test tube (I) will match the colour of the solution in test tube II when a piece of copper is dropped in it. This is because copper is less reactive than iron and will not displace iron from ferrous sulphate solution, resulting in no change in the colour of the solution.
(b) The colour of the ferrous sulphate solution will fade and a black mass will be deposited on the surface of the metal when a piece of aluminium or zinc is dropped in test tube III or IV. This is because aluminium and zinc are more reactive than iron and will displace iron from the ferrous sulphate solution, forming iron oxide (black mass) on their surfaces.
Q8. An ore on treatment with dilute hydrochloric acid produces brisk effervescence. Name the type of ore with one example. What steps will be required to obtain metal from the enriched ore? Also write the chemical equations for the reactions involved in the process. [AI 2019]
Ans. The ore that produces brisk effervescence when treated with dilute hydrochloric acid is a carbonate ore. One example of a carbonate ore is limestone (CaCO3).
Steps to obtain metal from the enriched ore:
Q9. Silver articles become black when kept in the open for some time, whereas copper vessels lose their shiny brown surfaces and gain a green coat when kept in the open. Name the substances present in the air with which these metals react and write the name of the products formed. 
Ans. The substances present in the air with which silver reacts are hydrogen sulphide (H2S) and sulphur compounds. Silver reacts with these substances to form a black layer of silver sulphide (Ag2S) on its surface. The substances present in the air with which copper reacts are moisture, carbon dioxide (CO2), and oxygen (O2). Copper reacts with these substances to form a green layer of copper carbonate (CuCO3) or copper hydroxide (Cu(OH)2) on its surface.
Q10. (a) What is reactivity series? How does the reactivity series help in predicting the relative activity of various metals?
(b) Suggest different chemical processes used for obtaining a metal from its oxides of metals in the middle and top of the reactivity series. Support your answer with one example. [CBSE Sample Paper 2018]
Ans. (a) The series of metals in decreasing order of reactivity is called the reactivity series of metals. The metals at the top are most reactive and metals at the bottom are least reactive.
(b) The metals in the middle of the reactivity series are obtained from their ores by chemical reduction with a suitable reducing agent, e.g.
ZnO + C → Zn + CO
The metals at the top of the series are obtained by electrolytic reduction of their molten orc.
Al2O3 → 2Al3+ + 3O2-
At cathode: 2Al3+ + 6e- → 2Al
At anode: O2- - 2e- → O
O + O → O2
Q11. Describe an activity to find out the conditions under which iron rusts. 
Ans. To find out the conditions under which iron rusts, you can perform the following activity:
Q12. A metal 'X' combines with a non-metal 'Y' by the transfer of electrons to form a compound Z.
(i) State the type of bond in compound Z.
(ii) What can you say about the melting point and boiling point of compound Z?
(iii) Will this compound dissolve in kerosene or petrol?
(iv) Will this compound be a good conductor of electricity? 
Ans. (i) The type of bond in compound Z is an ionic bond.
(ii) Ionic compounds generally have high melting and boiling points due to the strong electrostatic forces of attraction between the positive and negative ions.
(iii) Ionic compounds like compound Z do not dissolve in non-polar solvents like kerosene or petrol. They are only soluble in polar solvents.
(iv) No, compound Z will not be a good conductor of electricity in solid state because the ions are held in a fixed position and cannot move. However, it may conduct electricity when dissolved in water or in molten state as the ions become free to move and carry electric charge.
Q13. Why do some metal surfaces acquire a dull appearance when they are exposed to moist air? Write the color acquired by the surfaces of copper and silver in such a situation and also write the chemical names of the substances due to which it happens. [Board Term I, 2017]
Ans. When metal surfaces are exposed to moist air, they can undergo oxidation. This oxidation leads to the formation of metal oxides on the surface of the metal. In the case of copper, the surface acquires a greenish coating called copper(II) oxide (CuO). Copper(II) oxide gives the surface a dull appearance. In the case of silver, the surface acquires a blackish coating called silver sulfide (Ag2S). Silver sulfide also gives the surface a dull appearance.
Q14. Give reason for the following: [Board Term I, 2016]
(i) Hydrogen gas is not evolved when most of the metals react with nitric acid.
(ii) Zinc oxide is considered as an amphoteric oxide.
(iii) Metals conduct electricity.
Ans. (i) Most metals do not evolve hydrogen gas when they react with nitric acid because nitric acid is a strong oxidizing agent. It oxidizes hydrogen gas produced during the reaction to water and itself gets reduced to nitrogen oxides. Therefore, instead of hydrogen gas, the products obtained are nitrogen oxides.
(ii) Zinc oxide is considered an amphoteric oxide because it shows both acidic and basic properties. It reacts with acids to form zinc salts and water, exhibiting basic characteristics. Additionally, it reacts with bases to form zincates and water, showing acidic properties. This ability to react with both acids and bases classifies it as an amphoteric oxide.
ZnO + 2HCl → ZnCl2 + H2 O
ZnO + 2NaOH + H2 O → Na2 [Zn (OH)4 ]
(iii) Metals conduct electricity because they have a large number of free or delocalized electrons. These electrons are not bound to any particular atom and can move freely throughout the metal lattice. When a potential difference is applied across a metal, these free electrons can easily move and carry an electric current.
Q15. Reverse of the following chemical reaction is not possible: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) Justify this statement with reason. [Board Term I, 2016]
Ans. The reverse of the given chemical reaction is not possible because it violates the principle of conservation of mass. In the forward reaction, zinc (Zn) displaces copper (Cu) from copper sulfate (CuSO4) to form zinc sulfate (ZnSO4) and copper. However, in the reverse reaction, copper cannot displace zinc from zinc sulfate, as copper is less reactive than zinc. Hence, the reverse of this reaction is not feasible.
Q16. Why does the oxide of highly reactive metals cannot be reduced by carbon? [CBSE 2015]
Ans. It is because highly reactive metals themselves are stronger reducing agents than carbon.
Q17. What happens when carbon dioxide is compressed in water at higher pressure? [CBSE 2015]
Ans. Carbonic acid is formed.
CO2 + H2O → H2CO3
Q18. Write the chemical equation for the reaction taking place when steam is passed over hot aluminium. [CBSE 2015]
Ans. 2Al(s) + 3H2O (g) → Al2O3(s) + 3H2(g)
Q1. The following questions are source based/case based questions. Read the case carefully and answer the questions that follow. The melting points and boiling points of some ionic compounds are given below:
These compounds are termed ionic because they are formed by the transfer of electrons from a metal to a non-metal. The electron transfer in such compounds is controlled by the electronic configuration of the elements involved. Every element tends to attain a completely filled valence shell of its nearest noble gas or a stable octet.
(i) Show the electron transfer in the formation of magnesium chloride.
(ii) List two properties of ionic compounds other than their high melting and boiling points.
(iii) (A) While forming an ionic compound say sodium chloride how does sodium atom attain its stable configuration?
(B) Give reasons:
(i) Why do ionic compounds in the solid state not conduct electricity?
(ii) What happens at the cathode when electricity is passed through an aqueous solution of sodium chloride? 
Ans. (i) Transfer of electrons during the creation of magnesium chloride:
(ii) The two properties of ions Compounds are:
(a) Solubility: Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.
(b) Conduction of Electricity: The conduction of electricity through a solution involves the movement of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution. Ionic compounds in the solid state do not conduct electricity because movement of ions in the solid is not possible due to their rigid structure. But ionic compounds conduct electricity in the molten state. This is possible in the molten state since the elecrostatic forces of attraction between the oppositely charged ions are overcome due to the heat. Thus, the ions move freely and conduct electricity.
(iii) (A) Sodium atom has one electron in its outermost shell. If it loses the electron from its M shell then its L shell now becomes the outermost shell and that has a stable octet. The nucleus of this atom still has 11 protons but the number of electrons has become 10, so there is a net positive charge giving us a sodium cation Na+. On the other hand chlorine has seven electrons in its outermost shell and it requires one more electron to complete its octet. If sodium and chlorine were to react, the electron lost by sodium could be taken up by chlorine. After gaining an electron, the chlorine atom gets a unit negative charge, because its nucleus has 17 protons and there are 18 electrons in its K, L and M shells. This gives us a chloride anion Cl–.
(B) (i) The conduction of electricity through a solution involves the movement of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution. Ionic compounds in the solid state do not conduct electricity because movement of ions in the solid is not possible due to their rigid structure. But ionic compounds conduct electricity in the molten state. This is possible in the molten state since the elecrostatic forces of attraction between the oppositely charged ions are overcome due to the heat. Thus, the ions move freely and conduct electricity.
(ii) When electricity is passed through a solution of sodium chloride in water, hydrogen gas is released twice as much as oxygen gas is released at the anode.
Q2. The following questions are source based/case based questions. Read the case carefully and answer the questions that follow. Metals are required for a variety of purposes. For this we need their extraction from their ores. Ores mined from the earth are usually contaminated with many impurities which must be removed prior to the extraction of metals. The extraction of pure metal involves the following steps:
(1) Concentration of ore
(2) Extraction of metal from the concentrated ore
(3) Refining of metal
(a) Name an ore of mercury and state the form in which mercury is present in it.
(b) What happens to zinc carbonate when it is heated strongly in a limited supply of air?
(c) The reaction of a metal A with Fe2O3 is highly exothermic and is used to join railway tracks.
(I) Identify the metal A and name the reaction taking place.
(II) Write the chemical equation or the reaction of metal A with Fe2O3. 
Ans. (a) An ore of mercury is cinnabar, and mercury is present in it in the form of mercury sulfide (HgS).
(b) When zinc carbonate (ZnCO3) is heated strongly in a limited supply of air, it undergoes thermal decomposition to produce zinc oxide (ZnO), carbon dioxide (CO2), and water (H2O):
ZnCO3(s) → ZnO(s) + CO2(g)
(c) (I) The metal A in this case is iron (Fe), and the reaction taking place is called a thermite reaction or the thermite process.
(II) The chemical equation for the reaction of iron (A) with iron(III) oxide (Fe2O3) is:
2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
This reaction is highly exothermic and is used in various industrial applications, including joining railway tracks due to its high heat generation and the ability to melt and fuse metals together.
Q3. (a) Complete and balance the following chemical equations: 
(i) A I2O3 + HCI →
(ii) K2O + H2O →
(iii) Fe + H2O →
(b) An element 'X' displaces iron from the aqueous solution of iron sulphate. List your observations if the element 'X’ is treated with the aqueous solutions of copper sulphate, zinc sulphate and silver nitrate. Based on the observations arrange X, Zn, Cu and Ag in increasing order of their reactivities.
Ans. (a) Complete and balance the following chemical equations:
(i) AI2O3 + 6HCl → 2AlCl3 + 3H2O
(ii) K2O + H2O → 2KOH
(iii) Fe + 2H2O → Fe(OH)2 + H2
Based on the observations, the increasing order of reactivities is:
Cu < Ag < X < Zn
Q4. (i) By the transfer of electrons, illustrate the formation of bond in magnesium chloride and identify the ions present in this compound. 
(ii) Ionic compounds are solids. Give reasons.
(iii) With the help of a labelled diagram show the experimental set up of action of steam on a metal.
(ii) Ionic compounds are solids because the particles which make up ionic compounds are held together by strong electrostatic bonds.
Q5. (a) (i) Write two properties of gold which make it the most suitable metal for ornaments.
(ii) Name two metals which are the best conductors of heat.
(iii) Name two metals which melt when you keep them on your palm.
(b) Explain the formation of ionic compound CaO with electron-dot structure. Atomic numbers of calcium and oxygen are 20 and 8 respectively. 
Ans. (a) (i) The malleability and ductility properties of gold make it suitable for ornaments. (ii) Silver and gold.
(iii) Gallium and caesium have so low melting points that they melt even on keeping them on palm.
Q6. Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. Why? Where are these metals placed in the reactivity series? How are these metals obtained form their ores? Take an example to explain the process of extraction along with chemical equations. 
Ans. Sodium, magnesium and aluminium have higher affinity towards oxygen than that of carbon because these are highly reactive metals. Hence, carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. These metals are placed at the top of the reactivity series. The highly reactive metals like Na, Mg, Al, etc. are extracted by electrolytic reduction of their molten chlorides or oxides. Electrolytic reduction is brought about by passing electric current through the molten state. Metal gets deposited at the cathode.
NaCl ⇌ Na+ + Cl–
At cathode : Na+ + e– → Na
At anode : 2Cl– → Cl2 + 2e–
Q7. Write balanced chemical equations to explain what happens, when
(i) Mercuric oxide is heated.
(ii) Mixture of cuprous oxide and cuprous sulphide is heated.
(iii) Aluminium is reacted with manganese dioxide.
(iv) Ferric oxide is reduced with aluminium.
(v) Zinc carbonate undergoes calcination. 
Ans. (i) On heating, mercuric oxide decomposes to give mercury .and oxygen.
(ii) On heating mixture of cuprous oxide and cuprous sulphide, copper and sulphur dioxide are produced.
(iii) When aluminium is heated with manganese dioxide, manganese and aluminium oxide are formed.
(iv) Ferric oxide reacts with aluminium to produce aluminium oxide and iron.
(v) On calcination, zinc carbonate produces zinc oxide and carbon dioxide.
Q8. (a) Name the following: 
(i) Metal that can be cut by knife
(ii) Lustrous non-metal
(iii) Metal that exists in liquid state at room temperature
(iv) Most malleable and ductile metal
(v) Metal that is best conductor of electricity
(vi) Non-metal that can exist in different forms
(b) How are alloys better than metals? Give composition of solder and amalgam.
Ans. (a) (i) Sodium
(b) Alloys are stronger than the metals from which they are made, more resistant to corrosion, have lower melting point, have lower electrical conductivity. Solder is an alloy of lead and tin. An amalgam is an alloy of mercury with another metal.
Q9. (a) List in tabular form three chemical properties on the basis of which we can differentiate between a metal and a non-metal.
(b) Give reasons for the following:
(i) Most metals conduct electricity well.
(ii) The reaction of iron (III) oxide [Fe2O3] with heated aluminium is used to join cracked machine parts. [Delhi 2019]
(b) (i) Metals conduct electricity due to the flow of free electrons present in them.
(ii) The reaction of iron (III) oxide, Fe2O3 with aluminium is highly exothermic and the iron produced melts. This molten iron is used to join cracked iron parts of machines and railway tracks.
Q10. (a) Write the steps involved in the extraction of pure metals in the middle of the activity series from their carbonate ores.
(b) How is copper extracted from its sulphide ore? Explain the various steps supported by chemical equations. Draw labelled diagram for the electrolytic refining of copper. 
Ans. (a) Extraction of metals of medium reactivity: The metals in the middle of the reactivity series are zinc, iron, lead, etc. The carbonate ores first need to get converted to oxides as it is easier to get metal from their oxides.
(b) Copper glance (Cu2S) when heated in air gets partially oxidised to copper oxide which further reacts with the remaining copper glance to give copper metal.
Q11. Draw a schematic diagram of the various steps involved in the extraction of metals from ores for metals of medium reactivity and for metals of low reactivity. [Board Term I, 2018]
Ans. Various steps involved in the extraction of a metal from its ore followed by refining of the metal is called ‘metallurgy’. The steps involved are summarised as follows :
Q12. (a) Define corrosion.
(b) What is corrosion of iron called?
(c) How will you recognise the corrosion of silver?
(d) Why corrosion of iron is a serious problem?
(e) How can we prevent corrosion of iron? (Board Term I, 2017)
Ans.(a) The process of slowly eating up of metals due to their conversion into oxides, carbonates, sulphides, etc., by the action of atmospheric gases and moisture is called corrosion.
(b) The corrosion of iron is called rusting.
(c) Silver articles become black after sometime when exposed to air. This is due to formation of a coating of black silver sulphide (Ag2S) on its surface by the action of H2S gas present in the air.
(d) Corrosion of iron is a serious problem. Every year large amount of money is spent to replace damaged iron articles. Corrosion causes damage to car bodies, bridges and iron railings, ships and to all objects made of metals specially those of iron.
(e) Corrosion of iron is prevented by coating it with a layer of oil. The reason being that the layer of oil does not allow air and water to react the surface of iron. Corrosion of iron can also be prevented by painting, greasing, galvanising, anodising, electroplating or making alloys.
Q13. (a) Define corrosion. [CBSE 2016]
(b) What is corrosion of iron called?
(c) How will you recognise the corrosion of silver?
(d) Why corrosion of iron is a serious problem?
(e) How can we prevent corrosion of iron?
Ans. (a) It is a process in which a metal reacts with substances present in the air to form surface compounds.
(c) Black layer on its surface due to formation of Ag2S.
(d) It makes the metal weak and brittle, which is a serious problem.
(e) Oiling, painting, greasing, galvanisation, alloying can prevent iron from corrosion.
Q14. (a) Define corrosion, what name is given to the corrosion of iron?
(b) Name the colour of the coating formed on silver and copper articles, when exposed to air?
(c) List two damages caused by corrosion and suggest how corrosion can be prevented. [CBSE 2016]
Ans. (a) When a metal is attacked by substances around it, such as moisture, acids, etc., it is said to corrode and this process is called corrosion. Corrosion of iron is called rusting.
(b) Coating formed on silver is black and that formed on copper is green.
(c) Damages caused by corrosion:
Prevention of corrosion:
Q15. Give reasons for the following: [CBSE 2016]
(i) Carbonate and sulphide ores are usually converted into oxides during the process of extraction of metals.
(ii) Ionic compounds have generally high melting points.
(iii) Hydrogen is not a metal, but it has been assigned a place in the reactivity series of metals.
(iv) The galvanised iron article is protected against rusting even if the zinc layer is broken.
(v) The wires carrying current in homes have a coating of PVC.
Ans. (i) It is easier to convert metal oxides to metals as compared to carbonates and sulphides. Therefore carbonates are calcinated and sulphides are roasted to oxides.
(ii) There are electrostatic forces of attraction between the cations and anions in ionic compounds which are difficult to break. Therefore ionic compounds have high melting points.
(iii) Metals above hydrogen evolve hydrogen gas and metals below hydrogen do not evolve hydrogen when treated with an acid. That is when hydrogen has been assigned a place in the reactivity series of metals.
(iv) Even if the zinc layer is broken, it will preferentially be oxidised because it is more reactive than iron.
(v) The wires carrying current in homes have a coating of PVC. This is because PVC is an insulating substance and protects from electric shock.
Q16. (a) Write electron dot structure for chlorine (At No. 17) and calcium (At No. 20). Show the formation of calcium chloride by the transfer of electrons.
(b) Identify the nature of the above compound and explain the three physical properties of such compounds. [CBSE 2015]
(b) It is an ionic compound.
(i) It is hard and solid.
(ii) It has high melting and boiling point.
(iii) It is soluble in water.
|1. What are some examples of metals and non-metals?|
|2. How are metals and non-metals different from each other?|
|3. Can metals and non-metals react with each other?|
|4. What are the physical properties of metals?|
|5. What are the uses of metals and non-metals in everyday life?|