TEXTUAL QUESTIONS PAGE – 40
Q.1- Give an example of a metal which :
(i) is a liquid at room temperature.
(ii) can be easily cut with a knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.
Ans- (i) Mercury
Q.2- Explain the meaning of malleable and ductile.
Ans- Malleable – A substance is said to be malleable if it can be beaten into sheets.
Ductile – A substance is said to be ductile if it can be drawn into wires.
TEXTUAL QUESTIONS PAGE – 46
Q.1- Why is sodium kept immersed in kerosene oil?
Ans- Sodium is highly reactive. It catches fire if kept in the open. To prevent its reaction with oxygen, moisture and carbon dioxide, it is kept immersed in kerosene oil.
Q.2- Write equations for the reactions of :
(i) iron with steam
(ii) calcium and pottasium with water
(i) 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
(ii) Ca(s) + 2H2O(I) → Ca(OH)2(aq) + H2(g)
2K(s) + 2H2O(I) → 2KOH(aq) + 2H2(g)
Q.3- Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows :
Use the table above to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal?
(ii) What would you observe if B is added to a solution of copper (II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
Ans- (i) B is the most reactive metal.
(ii) B will displace copper from copper sulphate solution.
(iii) The decreasing order of reactivity is :
B > A > C > D
Q.4- Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
Ans- Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.
Fe(s) + H2SO4(aq) →FeSO4(aq) + H2(g)
Q.5- What would your observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
Ans- When zinc is added to a solution of iron (II) sulphate, it will displace iron from it and light green colour of solution fades away.
FeSO4 + Zn → ZnSO4 + Fe(s)
TEXTUAL QUESTIONS PAGE – 49
Q.1- (i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?
Ans- (i) Electron-dot structures for sodium, oxygen and magnesium:
(ii) Formation of Na2O :
Formation of MgO :
(iii) The ions present in Na2O are Na+ and O2-
The ions present in MgO are Mg2+ and O2-
Q.2- Why do ionic compounds have high melting points?
Ans- In ionic compounds, there are strong forces of attraction between the oppositely charged ions. A large amount of energy is required to break these forces and to melt the ionic compounds. That’s why the ionic compounds have high melting points.
TEXTUAL QUESTIONS PAGE – 53
Q.1- Define the following terms :
(i) Mineral (ii) Ore (iii) Gangue
Ans- (i) Mineral – The element or compound which occurs naturally in the earth’s crust is called mineral.
(ii) Ore – An ore is a mineral from which metal can be extracted.
(iii) Gangue – The earthly impurities such as sand, lime, stone, rocks etc. associated with minerals and ores are collectively known as gangue.
Q.2- Name two metals which are found in nature in the free state.
Ans- Gold and Platinum.
Q.3- What chemical process is used for obtaining a metal from its oxide?
Ans- Reduction process.
TEXTUAL QUESTIONS PAGE – 55
Q.1- Metallic oxides of zinc, aluminium and copper were heated with the following metals :
In which cases will you find displacement reactions taking place?
Ans- Zinc can displace copper from copper oxide.
Zn + CuO → ZnO + Cu
Magnesium can displace zinc from zinc oxide.
Mg + ZnO → MgO + Zn
Q.2- Which metals do not corrode easily?
Ans- The metals which are not attacked by air and moisture do not corrode easily. Eg- Gold and platinum.
Q.3- What are alloys?
Ans- Alloys are the homogeneous mixtures of two or more metals or metals and non-metals.
TEXT BOOK EXERCISE PAGE – 56, 57
Q.1- Which of the following pairs will give displacement reactions :
(a) NaCl solution and copper metal.
(b) MgCl2 solution and aluminium metal.
(c) FeSO4 solution and silver metal.
(d) AgNO3 solution and copper metal.
Ans- (d) AgNO3 solution and copper metal.
Q.2- Which of the following method is suitable for preventing an iron frying pan from rusting :
(a) applying grease
(b) applying paint
(c) applying a coating of zinc
(d) All of the above
Ans- (c) Applying a coating of zinc.
Q.3- An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be :
Ans- (a) calcium
Q.4- Food cans are coated with tin and not with zinc because :
(a) zinc is costlier than tin.
(b) zinc has a higher melting point than tin
(c) zinc is more reactive than tin
(d) zinc is less reactive than tin
Ans- (c) zinc is more reactive than tin.
Q.5- You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
Ans- (a) Set up the electric circuit as shown below :
To distinguish between metals and non-metals on the basis of their electrical conductivity, insert the sample to be tested between clips A and B. If the bulb glows, the sample is metal. If the bulb doesn’t glow, the sample is non-metal.
Thus metals are good conductor of electricity whereas non-metals are poor conductors of electricity.
(b) These tests are useful in distinguishing between the properties of metals and non-metals.
Q.6- What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans- The metal oxides which react with both acids and bases to produce salts and water are known as amphoteric oxides.
Examples – Zinc oxide ( ZnO )
Aluminium oxide ( Al2O3 )
Q.7- Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Ans- Zinc and magnesium will displace hydrogen from dilute acids.
Copper and silver will not displace hydrogen from dilute acids.
Q.8- In the electrolytic refining a metal M, what would you take as the anode, the cathode and the electrolyte?
Ans- During electrolytic refining of metal M, the impure metal is made as anode, a thin strip of pure metal M is made as cathode. The electrolyte used is a soluble salt of metal M to be refined.
Q.9- Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it as shown in the figure.
(a) What will be the action of gas on :
(i) dry litmus paper
(ii) moist litmus paper
(b) Write a balanced chemical equation for the reaction taking place.
Ans- (a) (i) No action will take place.
(ii) It turns moist litmus paper red and then bleaches it.
(b) S(s) + O2(g) → SO2(g)
Q.10- State two ways to prevent rusting of iron.
Ans- The rusting of iron can be prevented :
(i) By painting, oiling, greasing, galvanising, chrome plate or anodising.
(ii) By making alloys.
Q.11- What type of oxides are formed when non-metals combine with oxygen?
Ans- When non-metals combine with oxygen, two types of oxides are formed :
(a) Neutral oxides – CO, NO etc.
(b) Acidic oxides – SO2, CO2 etc.
Q.12- Give reasons :
(a) Platinum, Gold and Silver are used to make jewellery.
(b) Sodium, pottasium and lithium are stored under oil.
(c) Aluminium is highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Ans- (a) Platinum, gold and silver are used to make jewellery because these are not attacked by air and moisture. They don’t undergo corrosion and retain their lustre for a long time. Also, these metals are malleable and ductile.
(b) Sodium, pottasium and lithium are stored under oil because they are very reactive and catch fire when exposed to air.
(c) This is due to the reason that aluminium forms a thin layer of aluminium oxide on its surface which prevents aluminium to react with other substances. Also, aluminium is a good conductor of heat.
(d) This is because it is easier to obtain a metal from its oxide as compared to its sulphide and carbonate ores.
Q.13- You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Ans- In tarnished copper vessels there is a layer of basic copper carbonate. This basic layer can be cleaned by using sour substances such as lemon or tamarind juice which are acidic in nature. These substances dissolve the basic coat of copper carbonate.
Q.14- Differentiate between metals and non-metals on the basis of their chemical properties.
Q.15- A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him, which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Ans- The solution used by goldsmith to bring back the glitter of old and dull gold ornaments was aqua regia. It is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3:1. It can dissolve gold.
Q.16- Give the reason why copper is used to make hot water tanks and not steel ( an alloy of iron)
Ans- This is because steel corrodes easily, but copper does not corrode easily. As a result, the body of steel tank become weak. Also, copper does not react with water at any temperature whereas iron reacts with water on heating.