SHORT ANSWER TYPE QUESTIONS
Q.1. Explain the following: [Delhi 2019]
(a) Sodium chloride is an ionic compound which does not conduct electricity in solid state whereas it does conduct electricity in molten and solid state as well as in aqueous solution.
(b) Reactivity of aluminium decreases if it is dipped in nitric acid.
(c) Metals like calcium and magnesium are never found in their free state in nature.
Ans. (a) • Sodium chloride is an ionic compound because it is made up of Na+ and CP- ions.
• It does not conduct electricity in solid state because ions are not free to move.
• It conducts electricity in molten state because ions are free to move.
(b) It is due to formation of oxide layer on its surface which makes it passive (less reactive) HNO3 is good oxidising agent.
(c) It is because Mg and Ca are highly reactive, react with other elements to form compounds, therefore, are not found in free state.
Q.2. (a) What is reactivity series? How does the reactivity series help in predicting the relative activity of various metal?
(b) Suggest different chemical processes used for obtaining a metal from its oxides of metals in the middle and top of 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 reactivity series are obtained from their ores by chemical reduction with suitable reducing agent, e.g.
ZnO + C aa Zn + CO
The metals at the top of series are obtained by electrolytic reduction of their molten orc.
Q.3. Explain the following statements: [CBSE 2016]
(a) Most metal oxides are insoluble in water but some of these dissolve in water. What are these oxides and their solutions in water called?
(b) At ordinary temperature the surface of metals such as magnesium, aluminium, zinc, etc. is covered with a thin layer. What is the composition of this layer? State its importance.
(c) Some alkali metals can be cut with a knife.
Ans. (a) Solution o f metal oxides in water is called alkali (soluble base), e.g. sodium hydroxide (NaOH), potassium hydroxide (KOH).
(b) This layer is an oxide layer. It makes the metal less reactive (passive) and makes it more useful because it cannot get corroded and remains as it is.
(c) It is because these metals are very soft, e.g. sodium metal can be cut with a knife.
Q.4. Write one example of each of the following: [CBSE 2016]
(a) Most malleable metal and most ductile metal.
(b) The best conductor of heat and the poorest conductor of heat.
(c) A metal with highest melting point and a metal with lowest melting point.
Ans. (a) Gold is the most malleable and ductile metal.
(b) Silver is the best conductor, whereas lead is a poor conductor of heat.
(c) Tungsten has the highest melting point, Mercury has the lowest melting point.
Q.5. Write one example of each of the following:
(a) A metal and a non-metal which are liquids at room temperature.
(b) A metal which is very soft and a non-metal which is very hard.
(c) A metal which has very low melting point and a non-metal which has very high melting point. [CBSE 2016]
Ans. (a) Mercury is a metal, bromine is non-metal, liquid at room temperature.
(b) Sodium is very soft metal, diamond is very hard non-metal.
(c) Gallium has low melting point, diamond has very high melting point.
Q.6. State two properties of each of the following metals which make them suitable for: [CBSE 2016]
(i) Copper and aluminium for making electric wires.
(ii) Gold, platinum and silver are used to make jewellery.
(iii) Copper to make hot water tank.
Ans. (i) Copper and aluminium are ductile and good conductors of electricity.
(ii) Gold, platinum and silver are malleable and ductile.
(iii) Copper is malleable and good conductor of heat.
Q.7. Describe how sodium and chlorine form sodium chloride ? Name the type of bonding shown in the structure. (Atomic number : Na - 11, Cl - 17) [CBSE 2016]
There is ionic bonding between sodium and chloride ions.
Q.8. Write the names and symbols of the constituents present in the following alloys: [CBSE 2016]
Q.9. What is cinnabar? How is metal extracted from cinnabar? Explain briefly. [CBSE 2015]
Ans. Cinnabar is HgS
Mercury is obtained by roasting cinnabar. HgO formed is thermally unstable and gives mercury.
Q.10. (a) Write the electron dot structures for potassium and chlorine.
(b) Show the formation of KCI by the transfer of electrons.
(c) Name the ions present in this compound, KCI. [CBSE 2015]
Q.11. State three reasons for the following facts: [CBSE 2015]
(a) Sulphur is a non-metal
(b) Magnesium is a metal
One of the reasons must be supported with a chemical equation.
|(a) Sulphur is a non-metal||(b) Magnesium is a metal|
|(i) Poor conductor of heat and electricity.||(i) Good conductor heat and electricity.|
|(ii) Neither malleable nor ductile.||(ii) Malleable and ductile|
|(iii) S + O2 → SO2|
Sulphur dioxide is acidic oxide.
|2Mg + O2 → 2MgO|
Magnesium oxide is basic in nature.
Q.12. Why does 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.
Q.13. What happens when carbon dioxide is compressed in water at higher pressure? [CBSE 2015]
Ans. Carbonic acid is formed.
Q.14. 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)
LONG ANSWER TYPE QUESTIONS
Q.1. (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. [CBSE 2018]
Ans. (a) Steps involved:
Taking the case of zinc carbonate:
3. Purification is done by electrolytic refining.
(b) Copper is found in nature as Cu2S. It can be obtained from the ore just by heating in air.
Electrolytic refining of copper is done as shown in the diagram here.
Q.2. Distinguish between metals and non-metals on the basis o f (i) two physical and (ii) three chemical properties. [CBSE 2018 for Blind]
Q.3. (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 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 serious problem.
(e) Oiling, painting, greasing, galvanisation, alloying can prevent iron from corrosion.
Q.4. (a) Define corrosion, what name is given to the corrosion of iron?
(b) Name the colour of 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:
(i) It causes damage to car bodies and bridges.
(ii) It damages iron railings and ships.
Prevention of corrosion:
(i) Corrosion can be prevented by oiling, painting, greasing and galvanising.
(ii) Corrosion can be prevented by galvanising and alloying.
Q.5. 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 com pounds have generally high m elting 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 zinc layer is broken, it will preferentially 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.
Q.6. (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 three physical properties of such compounds. [CBSE2015]
(b) It is ionic compound.
(i) It is hard and solid.
(ii) It has high melting and boiling point.
(iii) It is soluble in water.
Q.7. (a) Describe an activity to show that metals are good conductors of electricity.
(b) Account for the following:
(i) Hydrogen gas is not evolved when a metal reacts with nitric acid.
(ii) For storing sodium metal, it is kept immersed in kerosene.
(iii) The reaction of iron (III) oxide with aluminium is used to join cracked iron part machines. [CBSE 2015]
(1) Set up an electric circuit as shown in the figure.
(2) Place the metal to be tested in the circuit between terminals A and B as shown.
(3) We find that the bulb glows. This shows that metals are good conductors of electricity.
(b) (i) This is because the hydrogen gas first evolved reacts with HNO3 to produce oxides of nitrogen.
(ii) We cannot store it under water because sodium reacts with water to produce hydrogen gas.
2Na + 2H2O → 2NaOH + H2
(iii) Fe2O3 + 2AI → AI2O3 + 2Fe + Heat
This is exothermic reaction. The molten iron is used to join cracked iron parts of machine.
Q.8. (a) When calcium metal is added to water, the gas evolved does not catch fire but the same gas evolved on adding potassium metal to water catches fire. Explain why?
(b) Name a metal for each case :
(i) It displaces hydrogen gas from nitric acid.
(ii) It does not react with any physical state of water.
(iii) It does not react with cold as well as hot water but reacts with steam. [CBSE 2015]
Ans. (a) Reaction of potassium with water is so violent and exothermic that the evolved hydrogen catches fire.
The reaction of calcium with water is less violent. The heat evolved is not sufficient for hydrogen to catch fire.
(b) (i) Magnesium
Q.9. (a) In column I are given different methods of extraction. Name the methods used for the extraction of metals given in column II:
(b) Differentiate between roasting and calcination processes giving one example of each. [CBSE2015]
(b) Roasting : The sulphide ore is converted into oxide by heating in the presence of excess air. This is called roasting. The following reaction takes place:
Calcination: The carbonate ore is converted into oxide by heating in limited air. This process is known as calcination. The following reaction takes place :
Q.10. In the formation of a compound XY2, atom X donates one electron to each Y atom. Show the electron dot structure of X and Y and the formation of XY2. What is the nature of bond in XY2? Write any three properties of compound XY2. The electronic configurations of the elements X and Y are as follows: [CBSE 2015]
X - 2, 8, 2 Y - 2, 7
The nature of bonds in XY2 is ionic.
(i) Ionic compounds have high melting and boiling points.
(ii) Ionic compounds are generally soluble in water and insoluble in kerosene and petrol.
(iii) Solutions of ionic compounds conduct electricity. Molten state of such compounds also conduct electricity.