Page no – 40
Solution 1
(i) Metal that exists in liquid state at room temperature ➜ Mercury
(ii) Metal that can be easily cut with a knife ➜ Sodium
(iii) Metal that is the best conductor of heat ➜ Silver
(iv) Metals that are poor conductors of heat ➜ Mercury and lead
Concept comprehension: For answering this question, recall the metals which have the properties stated in the question. If only name of the metal is asked, write the name only.
Solution 2
Malleable: Substances that can be beaten into thin sheets on hammering are called malleable. For example – most of the metals like gold are malleable.
Ductile: Substances that can be drawn into thin wires are called ductile. For example -most of the metals like copper and aluminium are ductile.
Concept comprehension: For answering this question, write the complete definition of melleable and ductile. Remember the key words – malleable related to thin sheets and ductile related to wires.
Page no – 46
Solution 1Sodium is a very reactive metal. It combines explosively with air as well as water. Hence, it catches fire if kept in open. Therefore, to prevent accidental fires and accidents, sodium is kept immersed in kerosene oil.
Concept comprehension: The key to this answer is that sodium is a very reactive metal.
Solution 2
(i) 3 Fe (s) + 4 H2O (g) ➜ Fe3O4 (s)+ 4 H2( g)
(ii) Ca(s) + 2 H2O(l) ➜ Ca(OH)2 (aq) + H2 (g) + Heat
(iii) 2K (s) + 2 H2O(l) ➜ 2 KOH (aq) + H2 (g) + Heat
Concept comprehension: For answering this question , write the balanced chemical equations.
Solution 3
(i) B is the most reactive metal.
(ii) When metal B is added to a solution of copper (II) sulphate, a displacement reaction occurs due to which blue colour of copper sulphate solution fades and a red brown coating of copper forms on B.
B + CuSO4 ➜ Displacement
(iii) The arrangement of the metals in the order of decreasing reactivity is:
B > A > C > D
Concept comprehension: The key to this answer is displacement reaction. A displacement reaction takes place when a more reactive metal is able to displace a less reactive metal from its salt solution.
A + FeSO4 ➜ No reaction, i.e., A is less reactive than iron
A + CuSO4 ➜ Displacement, i.e., A is more reactive than copper
B + FeSO4 ➜ Displacement, i.e., B is more reactive than iron
B + ZnSO4 ➜No reaction, i.e., B is less reactive than zinc
C + FeSO4 ➜ No reaction, i.e., C is less reactive than iron
C + CuSO4 ➜ No reaction, i.e., C is less reactive than copper
C + ZnSO4 ➜ No reaction, i.e., C is less reactive than zinc
C + AgNO3 ➜ Displacement, i.e., C is more reactive than silver
D + FeSO4 / CuSO4 / ZnSO4 / AgNO3 ➜ No reaction, i.e., D is less reactive than iron, copper, zinc, and silver
Solution 4
Hydrogen gas is evolved when dilute hydrochloric acid is added to a reactive metal.
When iron reacts with dilute H2SO4, iron (II) sulphate with the evolution of hydrogen gas is formed.
Fe (s) + H2SO4 (aq) ➜ FeSO4 (aq) + H2 (g)
Concept comprehension: For answering this question, you need to recall the reaction between metals and dilute acids.
Solution 5
Zinc is more reactive than iron. Therefore, if zinc is added to a solution of iron (II) sulphate, then it would displace iron from the solution and a colourless solution of zinc sulphate is formed.Zn (s) + FeSO4 (aq) ➜ ZnSO4 (aq) + Fe (s)
Concept comprehension: For answering this question, recall the reaction between zinc is added to a solution of iron (II) sulphate.
Page no – 49
Solution 1
(i) The representation of elements with valence electrons as dots around the elements is referred to as electron-dot structure for elements.
(iii) The ions present in Na2O are Na+ and O2? ions and in MgO are Mg2+ and O2? ions.
Concept comprehension: For answering this question, remember that metals lose electrons and form positively charged cations. Non- metals gain electrons and form negatively charged anions.
Solution 2
Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces and melt the ionic compounds. That is why, ionic compounds have high melting points.
Concept comprehension: The key to this answer is in the type of bonding that exists in ionic compounds.
Page no – 53
Solution 1
(i) Mineral: The naturally occuring elements or compounds in the earth’s crust are known as minerals.
(ii) Ore: Minerals from which metals can be extracted conveniently and profitably are known as ores.
(iii) Gangue: The unwanted impurities (sand, silt, soil, gravel, etc.) present in the ore are called gangue.
Concept comprehension: For answering this question, write the proper definition of all the three terms.
Solution 2
The metals at the bottom of the reactivity series are mostly found in free state. For example: gold, silver and platinum.
Concept comprehension: The key to this answer is that what type of metals will exist in free state.
Solution 3
The chemical process used for obtaining a metal from its oxide is reduction. In this process, metal oxides are reduced by using suitable reducing agents such as carbon or by highly reactive metals to displace the metals from their oxides.
For example, zinc oxide is reduced to metallic zinc by heating with carbon.
Concept comprehension: The key to this answer is that the conversion of metal oxide to metal is a reduction of metal oxide.
Page no – 55
Solution 1
A more reactive metal displaces a less reactive metal from its oxide. Out of zinc, magnesium and copper, magnesium is the most reactive, zinc is less reactive and copper is the least reactive.
| Metal Zinc oxide Magnesium oxide Copper oxide | Zinc No reaction No reaction Displacemen | Magnesium Displacement No reaction Displacement | Copper No reaction No reaction No reaction |
Concept comprehension: The key to this answer is displacement reaction. A displacement reaction takes place when a more reactive metal is able to displace a less reactive metal from its salt solution.
Solution 2
Less reactive metals i.e. the metals which are at the bottom of the ‘reactivity series’ do not corrode easily. For example – gold.
Concept comprehension: More reactive a metal is, more likely it is to be corroded. Less reactive a metal is, less likely it is to get corroded.
Solution 3
Alloys are homogeneous mixtures of two or more elements. The elements could be two metals, or a metal and a non-metal.For example, steel is an alloy of iron and carbon.
Concept comprehension: For answering this question, write the comnplete definition of alloys with all the key words – homogeneous mixture, two or more elements.
Page no – 56
Solution 1(d) AgNO3 solution and copper metal
Concept comprehension: The key to this answer is displacement reaction. A displacement reaction takes place when a more reactive metal is able to displace a less reactive metal from its salt solution.
Solution 2
(c) Applying a coating of zinc
Concept comprehension: We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed.)
Solution 3
(a) The element is likely to be calcium
Concept comprehension: The key to this answer is to find which oxide has a high melting point and is also soluble in water.
Solution 4
zinc is more reactive than tin.
Concept comprehension: Food cans are coated with tin and not with zinc because zinc is more reactive than tin.
Solution 5
(a) With the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non-metal. Similarly, we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.
(b) The above tests are useful in distinguishing between metals and non-metals in some cases but not all because there are exceptions also. These tests are based on physical properties and no chemical reactions are involved in these tests.
Concept comprehension: A hammer can be used to test whether the element is malleable or not. If it can be beaten into thin sheets, it is malelable. Most metals are malleable. Similarly, most metals are good conductors of electricity. So, a battery, bulb, wires, and a switch can be used to set up a circuit.
Solution 6
Those oxides that behave as both acidic and basic oxides are called amphoteric oxides. They react with both acids as well as bases to form salts and water.
Examples: aluminium oxide (Al2O3), zinc oxide (ZnO)
Concept comprehension: In this answer, you should write the definition of amphoteric oxide. Remember that it shows the properties of both acidic and basic oxides.
Solution 7
Metals that are more reactive than hydrogen displace it from dilute acids. For example: sodium and potassium. Metals that are less reactive than hydrogen do not displace it. For example: copper and silver.
Concept comprehension: For this question, remember that a displacement reation will take place if a more reactive element displaces a less reactive element from its salt solution.
Page no – 57
Solution 1In the electrolytic refining of a metal M:
Anode ➜ Thick block of Impure metal M
Cathode ➜ Thin strip of pure metal M
Electrolyte ➜ Solution of salt of the metal M
Concept comprehension: Remember CP cathode – pure. So, Anode will be impure.
Solution 2
(a) (i) There will be no action on dry litmus paper.
(ii) Since the gas is sulphur dioxide (SO2), it turns moist blue litmus paper to red because sulphur dioxide reacts with moisture to form sulphurous acid.
(b) S (s) + O2 (g) ➜ SO2 (g)
Sulphur dioxide
Concept comprehension: Remember that sulphur when reacted in the presence of air will form its oxide. Also, since sulphur is a non- metal it will turn wet blue litmus paper red.
Solution 3
Two ways to prevent the rusting of iron are:
(i) Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
(ii) Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.
Concept comprehension: For answering this question, mention any two ways for prevention of rusting.
Solution 4
Answer 11:
Non-metals combine with oxygen to form acidic or neutral oxides.
2 C (s) + ½ O2 (g) ➜ 2 CO (g)
Neutral oxide
S (s) + O2 (g) ➜ SO2 (g)
Acidic oxide
Concept comprehension: Remember that non-metals combine with oxygen to form acidic or neutral oxides.
Solution 5
(a) Platinum, gold, and silver are used to make jewellery because they are very lustrous and are malleable. Also, they are very less reactive and do not corrode easily.
(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water. Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.
(c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides
Concept comprehension: For answering reasoning questions, always write the exact answer of what is required. First read the question carefully, think about the answer and then explain.
Solution 6
Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.
Concept comprehension: For answering this question, recall that tarnishing is corrosion, how is corrosion caused and how can lemon or tamarind juice remove corrosion.