- Information
- AI Chat
Ncert solution cbse class 10 sci chap 3
Masters in business administration
Cambridge Group of Institutions
Recommended for you
Preview text
In-text questions set 1 Page number 40
- 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?
Solution:
(i) Mercury is the metal which is liquid at room temperature
(ii) Sodium and potassium are the metals which can be cut with a knife
(iii) Silver is the best conductor of heat
(iv) Mercury is poor conductor of heat.
- Explain the meanings of malleable and ductile.
Solution:
i. Metals which can be beaten to sheets are said to be malleable ii. Metals which can be drawn into thin wires are said to be ductile
In-text questions set 2 Page number 46
Why is sodium kept immersed in kerosene oil? Solution: Sodium is a reactive metals, if kept open it will react with oxygen to explore and catch fire. Sodium metal is kept immersed in kerosene to prevent their reaction with oxygen, moisture and carbon dioxide of air.
Write equations for the reactions of
(i) iron with steam (ii) calcium and potassium with water
Solution: (i) Iron reacts with steam to form a magnetic oxide of Fe with the liberation of H 2.
3Fe(s) + 4H 2 O(g) → Fe 3 O 4 (s) + 4H 2 (g)
(ii) Calcium reacts with water to form calcium hydroxide and hydrogen. Ca(s) + 2H 2 O(I) → Ca(OH) 2 (aq) + H 2 (g)
Potassium reacts with cold water violently immediately with evolution of H2 which catches fire.
2K(s) + 2H 2 O(I) → 2KOH(aq) + 2H 2 (g)
- 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 Metal Iron(II) sulphate
Copper(II) sulphate
Zinc sulphate
Silver Nitrate
A No reaction Displacement - -
B Displacement - - -
C No reaction No reaction No reaction Displacement
D No reaction No reaction No reaction No reaction
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.
Oxygen:
Magnesium:
(ii) Formation of Magnesium oxide:
When magnesium reacts with oxygen, the magnesium atom transfers its two outermost electrons to an oxygen atom. By losing two electrons, the magnesium atoms form a magnesium ion (Mg2+) and by gaining two electrons, the oxygen atom forms an oxide ion (O2-).
Mg: + → MgO
Formation of Sodium oxide:
Two sodium atoms transfer their 2 outermost electrons to an oxygen atom. By losing two electrons, the two sodium atoms form tow sodium ions (2Na+). And by gaining two electrons, the oxygen atom forms an oxide ion (O2-).
(iii) The ions present in sodium oxide compound (Na 2 O) are sodium ions (2Na+) and oxide ions (O2-).
The ions present in Magnesium oxide compound (MgO) are magnesium ions Mg2+ and oxide ions (O2-).
- Why do ionic compounds have high melting points? Solution: Ionic compounds are the ones which has both positive and negative charges. Hence there will be strong force of attraction between them. This make expenditure of lot of heat to break this force of attraction hence ionic compounds have high melting points.
In-text questions set 4 Page number 53
- Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue Solution:
(i) Minerals are compounds (also known as elements) which are found naturally in the earth’s crust. E. Alums, K 2 SO 4 .Al 2 (SO 4 ) 3 .24H 2 O, etc. (ii) Ores are minerals from which metal can be extracted Ex: Bauxite Al 2 O 3 .2H 2 O is the ore of Al, copper pyrite CuFeS 2 .All minerals are not considered as ores but all ores are also minerals. (iii) Ores mined from the earth are naturally contaminated with sand, rocky materials. There are impurities present in the ore which are known as gangue.
Name two metals which are found in nature in the free state Solution: Gold and platinum are the two metals found in Free State in nature.
What chemical process is used for obtaining a metal from its oxide? Reduction method is used to obtain metal from its oxide. Ex: Zinc oxide is reduced to metallic zinc by Heating with carbon.
ZnO + C → Zn + CO
Exercise questions Page number 56-
- Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal (b) MgCl 2 solution and aluminium metal (c) FeSO 4 solution and silver metal (d) AgNO 3 solution and copper metal
Solution: Option d i AgNO 3 solution and copper is correct answer. Copper displace the silver cations (reducing them to the elemental metal), in the process copper itself being oxidised to Copper II cations (Cu2+) and going into solution. So silver metal precipitating out and a copper II nitrate solution will be remaining. Cu(s) + 2AgNO 3 (aq) → Cu(NO 3 ) 2 (aq) + 2Ag (s)
- Which of the following methods 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 Solution: Answer is (c) Applying a coat of Zinc Though applying grease and applying paint prevents iron from rusting but we cannot apply these methods on frying pan hence applying a coat of Zinc is most appropriate method to prevent an iron pan from rusting.
- 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
(a) Calcium (b) Carbon
(c) Silicon (d) Iron
Solution: Correct answer is option (a) i Calcium. Calcium reacts with oxygen to give calcium oxide. Calcium oxide is soluble in water to give Calcium Hydroxide. Carbon forms carbon-oxide with oxygen which is gas hence option B is wrong Silicon reacts with oxygen and forms silicon dioxide. This is insoluble in water. So option C is not correct. Iron reacts with oxygen and forms Iron dioxide. This is insoluble in water. So option D is not correct.
- 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.
Solution: Answer is c. Food cans are coated with tin and not with zinc because Zinc is more reactive that is electro positive than tin.
- 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. Solution: (a) Metals are malleable and can be easily drown into sheets by hitting with hammer. On the other hand if we beat non-metals they break down and they cannot be drawn into sheets as they are non-malleable. Metals of good conductors of electricity hence they
(b) Write a balanced chemical equation for the reaction taking place.
Solution: a) When sulphur powder is burnt in the air sulphur-di-oxide is formed. (i) Sulphur-di-oxide does not have any effect on dry litmus paper. (ii) Sulphur-di-oxide turn the moist litmus paper from blue to red as contact of SO 2 with water turns to sulfurous acid.
(b) S(s) + O 2 (g) → SO 2 (g) SO 2 (g) + H 2 O →H 2 SO 3
State two ways to prevent the rusting of iron. Solution:
Iron can be prevented from rusting by coating the surface of the iron with rust proof paints
By applying Oil/grease on the surface of iron objects as it will prevent the iron surface to get in contact with air consisting of moisture.
What type of oxides are formed when non-metals combine with oxygen? Solution: When non-metals combine with oxygen it forms either acidic or neutral oxides. Ex: N 2 O 5 or N 2 O 3 is an acidic oxide; CO is a neutral oxide.
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.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction
Solution:
(a) Platinum, gold and silver are used to make jewellery for these metals are very less reactive hence they are not affected by air, water or most chemicals. These metals have a lot of lustre and they are malleable and ductile in nature. (b) Sodium, potassium and lithium readily reacts with water to produce a lot of heat. As a result Hydrogen evolved in the reaction results in fire. On exposure to water they react with moisture (water droplets) present in the atmosphere, In order to prevent contact with water hence these metals are stored under oil.
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. Solution: Tarnished copper vessels being cleaned with lemon or tamarind because these sour substance contains acids which dissolve the coating of copper oxide or basic copper carbonate present on the surface or tarnished copper vessels. This makes them shining red-brown again. Hence they are very effective in cleaning tarnished copper vessels.
Differentiate between metal and non-metal on the basis of their chemical properties. Solution:
Metals Non-metals
When metals are heated with oxygen, they form ionic oxides which are basic in nature and form bases on dissolving with water. This turn red litmus paper to blue.
When non-Metals are heated with oxygen, they form covalent oxides which are acidic in nature which form acid on dissolving with water. This turn blue litmus paper to red.
They are electro positive, lose electrons readily and become a positive ion.
They are electro negative, gain electrons and become negative ions.
Metals are lustrous. Non-metals are non-lustrous; graphite is the exception
Ncert solution cbse class 10 sci chap 3
Course: Masters in business administration
University: Cambridge Group of Institutions
- Discover more from:
