3. Metals and Non-metals
Questions :
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.
Answer: (i) Mercury(Hg) is a metal which is liquid at room temperature.
(ii) Sodium(Na) can be easily cut with a knife.
(iii) Silver(Ag) is the best conductor of heat.
(iv) Lead(Pb) is a poor conductor of heat.
2. Explain the meanings of malleable and ductile.
Answer: Malleable: The term used for the metals that can be beaten into thin sheets.
Ductile: The term used for the metals that can be drawn into thin wires.
Questions :
1. Why is sodium kept immersed in kerosene oil?
Answer: Sodium is one of the most reactive metals and thus, it easily reacts with the atmospheric oxygen and moisture when kept in open. But, when it reacts the reaction is extremely violent and exothermic, which causes the evolved hydrogen to instantly catch fire and hence, there is a huge danger to life and property there. So, in order to avoid this danger it is kept in kerosene as it doesn't react with it. As, kerosene is a fluid of lesser density, sodium sinks in it and kerosene forms a layer above it which doesn't allow moisture, oxygen, CO2 and other gases to come in contact with it and so it doesn't react and remains for longer time in its pure form, which is essential for its use. Also, as it reacts vigorously with water it is bad to even think to store it in water.
2. Write equations for the reactions of
(i) Iron with steam
(ii) Calcium and potassium with water
Answer: (i) 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
(ii) Calcium with water: Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
Potassium with water: 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) + heat energy
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.
Answer: (i) Metal B is the most reactive metal. As, in the given metals Zn and Fe are most reactive in decreasing order and metal which displaces Zn is not given and the only metal which displaces Fe is Metal 'B'.
(ii) As, B can displace Fe which is more reactive than Cu, we would observe a displacement reaction between metal B and CuSO4 if B is added to CuSO4 which will result in deposition of precipitated Cu on metal B. Also, the color of CuSO4 will vanish gradually.
(iii) Metals in the order of decreasing reactivity: B > A > C > D. Reason, metals in the metal solutions in decreasing order of reactivity are Zn>Fe>Cu>Ag and B can displace Fe, A can displace Cu, C can displace Ag and D is not able to displace any of given metals.
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.
Answer: Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal. As, HCl is a strong acid and we are reacting it with a reactive metal.
Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)
5. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Answer: As, Zn is more reactive than Fe it will displace it from its compounds in solution, thus, we will observe displacement reaction which will change the color of solution from green to colorless. The chemical reaction that will take place is: Zn(s) + FeSO4(aq) → ZnSO4(aq) + Fe(s).
Questions :
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?
Answer: (i) Sodium:
Oxygen:
Magnesium:
(ii) Formation of Na2O: One electron from each of the 2 Sodium atom's valence shell transfer to 1 Oxygen atom resulting in formation of 2 Sodium cations and 1 Oxide anion.
Formation of MgO: 2 electron from the Magnesium atom's valence shell transfer to Oxygen atom resulting in formation of Magnesium cation and Oxide anion.
(iii) The ions present in compound "Sodium oxide" are: 2 Sodium cations [ 2Na+] and 1 Oxide anion [ O-].
The ions present in compound "Magnesium oxide" are: 1 Magnesium cation [ Mg+] and 1 Oxide anion [ O-].
2. Why do ionic compounds have high melting points?
Answer: Ions are made of cations and anions and hence have strong electrostatic force of attraction or inter-ionic attraction between them, and so to overcome this force of attraction or to rise its P.E and K.E, a large amount of energy is needed, which results in a higher melting point. As, at higher temperature average K.E of the particles will be higher which would be sufficient to start the process of rising P.E of the previously strongly attracted particles for fusion.
Questions :
1. Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue
Answer: (i) Mineral: The elements or compounds, which occur naturally in the earth’s crust, are known as minerals.
(ii) Ore: The minerals which contain a very high percentage of a particular metal and due to which the metal can be profitably extracted from it, are known as ores.v
(iii) Gangue: The impurities such as soil, sand, etc, by which the ores mined from the earth are usually contaminated in large amount are known as gangue.
2. Name two metals which are found in nature in the free state.
Answer: Gold(Au) and Platinum(Pt) are the two metals which are found in nature in the free state due to their extremely low reactivity.
3. What chemical process is used for obtaining a metal from its oxide?
Answer: Reduction process is used for obtaining a metal from its oxide which is usually done by heating or by using suitable reducing agents.
E.g: 2HgO(s) →Δ 2Hg(l) + O2(g)
Questions :
1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.
In which cases will you find displacement reactions taking place?
Answer: Displacement reaction takes place when a more reactive metal displaces a less reactive metal from its solution due to difference in their reactivities. In Zn, Mg, Cu, Zn is less reactive with respect to Mg, Mg is most reactive and Cu is least reactive. Also, a metal is not displaced by itself from its solution. So, we infer that displacement reaction will take place as follows, summarized in the table:
2. Which metals do not corrode easily?
Answer: Gold(Au) and platinum(Pt) are the metals which do not corrode easily, also copper and silver are the metals having low reactivity which relatively to reactive metals corrode less.
3. What are alloys?
Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal. It is prepared by first melting the primary metal, and then, dissolving the other elements in it, in definite proportions. It is then cooled to room temperature.
Exercises :
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.
Answer: Only the last pair that is option (d) AgNO3 solution and copper metal, will give displacement reaction. Explanation: As, displacement reaction happens only when a low reactive metal is displaced from its solution by more reactive metal. But, in (a) RNa > RCu; (b) RMg > RAl; (c) RFe > RAg and hence, displacement reaction are not possible. Now, in (d) RAg < RCu and so Cu displaces Ag to form copper nitrate and silver metal. The reaction is as follows: Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s).
2. 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.
Answer: (c) Applying a coating of zinc is the suitable method for preventing an iron frying pan from rusting. As, we use frying pan for cooking and hence, we cannot apply paint and grease on it, as they can cause bad effects on food and ultimately can become hazard for us. And also, they are not durable ways as due to heat they will not be able to stay long on the surface as on heating their structure will break down and it will be costlier, so for its solution galvanisation is the most suitable method as ZnO is recognized as safe material by F.A.D.A and also it doesn't decompose easily and is durable.
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
(a) calcium
(b) carbon
(c) silicon
(d) iron.
Answer: (a) calcium is the element. As, melting point of CaO is high about 2,572°C and it is soluble in water to form Ca(OH)2. But, CO2 is a gas and Fe2O3, SiO2 are insoluble in water.
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.
Answer: (c) zinc is more reactive than tin. And, hence can react with acids present in food and can form harmful salts. So, to avoid this a less reactive metal, Sn is used. Also, tin's price is usually 3 to 5 times more than Zn and melting point is not a considerable factor as atmospheric temperature never exceed 100°C on earth and food packed in cans is usually cold and even it is hot, it is less than 232°C the melting point of Sn. And also more reactive metal is never used till it is very much cheap and had negligible effect on health, which is not of case of Zn.
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.
Answer: (a) i. Metals are malleable and thus form metal sheets on beating with hammer on the other hand non-metals are brittle, we can use the hammer we have to try the substances given to change in form of sheets, if they then they are generally,metals and if doesn't then they are non-metals.
ii. Metals are usually good conductors of heat and non-metals are insulators. So, we can make a simple electric circuit with the battery, bulb, wires and the switch, with the substance attached in series in the circuit, then if it is metal then the bulb will glow on switching the switch "On" and if it is non-metal then the bulb will not glow on switching the switch "On".
(b) These, tests to check the properties of malleability and electrical conductivity of metals are very much useful for distinguishing between metals and non-metals as these properties are directly proportional to its chances of being a metal and inversely to be a non-metal and will show correct result, except in some cases like graphite and zinc.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer: The metal oxides which show both acidic and basic behaviour are known as amphoteric oxides. They react with both acids and bases to form salt and water.
E.g: i. Aluminium oxide:
Reaction with acid:- Al2O3 + 6HCl → 2AlCl3 + 3H2O.
Reaction with base: Al2O3 + 2NaOH → 2NaAlO2 + H2O.
ii. Zinc oxide:
Reaction with acid:- ZnO + 2HCl → ZnCl2 + H2O.
Reaction with base:- ZnO + 2NaOH → Na2ZnO2 + H2O.
7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer: The metals which will displace hydrogen from dilute acids are Aluminum(Al) and Sodium(Na), and two metals which will not displace hydrogen from dilute acids are gold(Au) and platinum(Pt). Reason: RAl > RH; RNa > RH and RAu < RH; RPt < RH, where R is the reactivity of metals and so more reactive metal will displace less reactive metal from its compound.
8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer: In the electrolytic refining of a metal M, it is good to take impure metal as anode as only metal in it is to be dissolved in electrolyte other impurities will be separated as anode mud, thin strip of pure metal 'M' as cathode as pure metal is to be deposited on it and we should get a complete pure metal and a suitable solution of 'M' metal salt as the electrolyte because the metal will deposit on the cathode only if metal concentration in electrolyte increases which will happen only when electrolyte is of the same metal's solution. As, the pure metal from the anode dissolves into the electrolyte on passing the current and an equivalent amount of pure metal from the electrolyte is deposited on the cathode. And, thus metal is refined.
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 figure below.
(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.
Answer: (a):- (i) There will be no effect of gas on dry litmus paper. The gas is SO2 formed after reaction of sulphur with atmospheric oxygen and is an acidic oxide. But, we know that acidic properties only come to play on litmus when hydrogen ion disassociation take place which needs acid and water, as here litmus paper is dry so there will not be formation of H2SO3 and hence it will not change color of litmus.
(ii) The gas will change the color of litmus from blue to red or from red to red. As, in this case litmus paper contains water which on contact with SO2 will form H2SO3 which will dissociate hydrogen in presence of water and will show acidic characteristics of changing litmus paper's color.
(b) The balanced chemical equation for the first reaction: S(s) + O2(g) →Δ SO2(g)
Second reaction: SO2(g) + H2O(l) → H2SO3(aq)
10. State two ways to prevent the rusting of iron.
Answer: i. Applying paint on iron object. As, the paint will form a coating on iron and will not allow moisture and atmospheric oxygen to come in contact with it and hence will decrease the rate of rusting.
ii. Galvanisation of iron object. As, the zinc layer coated on it will rust and will then further will not allow moisture and atmospheric oxygen to come in contact with inner part and hence will prevent rusting.
iii. Alloying of iron object. As, after alloying desired properties comes in the alloy, of which one is prevention from rusting. Like, stainless steel, alloy of Fe, C, Ni, Cr.
The following ways are in increasing effectivity and durability from top to bottom but also, with increasing cost.
11. What type of oxides are formed when non-metals combine with oxygen?
Answer: Non-metals usually form acidic oxides on combining with oxygen. But, they also form neutral oxides. E.g: CO2 is an acidic oxide and CO a neutral oxide.
12. 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.
Answer: (a) The fundamental reason why Pt, Au and Ag are used to make jewellery is due to their lustre which attracts every human. Then, is their property of resistance to corrosion as they are the least reactive metals they doesn't react easily even with acids and are extremely durable. And last is their malleability and ductility as sharp and beautiful designs can be carved on a small and light piece of metal too. Au is the most malleable metal and Pt is the most ductile metal.
(b) These all are very reactive metals and react easily with the atmospheric oxygen and moisture in an exothermic reaction producing tremendous amount of heat, which had potential to cause lot of destruction. Also, for experiments they doesn't remain in pure form so to avoid this they are kept in oil, which is lighter and hence these metals sink in them and then oil creates a protective layer on top of them which doesn't allow O2 or H2O and thus, keeping it as it is without any explosion.
(c) Al itself is a highly reactive metal and quickly forms a layer of Al2O3. But, once covered with Al2O3 then oxidation stops as it is a less reactive compound and prevents further oxidation by acting as a shield. Utensils made of Al are covered with Al2O3. So, as it is less reactive it doesn't react more and is safe to a good limit and hence brought in making of utensils for cooking.
(d) The reason is that extraction of metals directly from their oxide ores by reduction method is much easy than directly from carbonate and sulphide ores. And, conversion of carbonate and sulphide ores into oxide ores is comparatively easy so to reduce cost and use of energy, calcination or roasting is done.
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.
Answer: The reason behind their tarnishing is corroded Cu compounds. Sour lemon and tamarind contains citric and tartaric acid which dissolve the layer of corroded copper componds like CuO, Cu(OH)2, CuCO3 after which the lustrous copper metal under the tarnished layer becomes visible and the vessel is said to be cleaned. That's why these sour substances are effective in cleaning the vessels.
14. Differentiate between metal and non-metal on the basis of their chemical properties.
Answer: Metal:
i. They are electropositive in nature.
ii. They form basic oxides or sometime amphoteric oxides on combining with oxygen.
iii. They react with water to form metal oxide and release hydrogen gas. Their oxides on reacting with water form metal hydroxide.
iv. They react with acids usually, to form salts and release H2.
v. They displaces less reactive metal if added in a salt solution of less reactive metal. And, remains as it is in a salt solution of more reactive metal.
vi. They react with non-metals to form ionic or electrovalent compound.
vii. They can be easily extracted from their oxides than from their carbonates and sulphides.
viii. They react with O2 and H2O and corrode.
Non-metal:
i. They are electronegative in nature.
ii. They form acidic oxides or sometime neutral oxides on combining with oxygen.
iii. Their oxides on reacting with water form acids.
iv. Their non-metal oxides react with bases usually, to form salts and water.
v. They react with metals to form ionic or electrovalent compound.
vi. They are usually extracted by fractional distillation.
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?
Answer: Yes, the solution is an acidic solution named Aqua Regia, which is a mixture of HNO3 and HCl in a molar ratio of 1:3. It can dissolve noble metals like, Ag,Au,Pd and Pt which are signs of royalty and hence it is also called Royal or Regal water. Surprisingly, HCl a strong acid can't dissolve Au alone but after mixing with a weak acid it can do so, this is because HNO3 is a strong oxidising agent and thus, tries to gain electrons from inert Au and thus forming a cation, at the same time, HCl readily provides its chloride ions, to the cation and it becomes AuCl4 and hence, Au is separated from the object made of gold. Also, there is a huge importance of this solution in cleaning and manufacturing of an electrolyte, HAuCl4 for the best purification of gold.
16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer: The main reason is as from hot water, the steam is continuously generated for some time which can react instantly with Fe present in steel and can rust it, forming rust which have bad look, which can then suspend in water and can even change color of water, also, it weakens the tank due to the corrosion and decreases its life. To find a solution for it copper tanks are used as copper being a less reactive metal doesn't react with steam or water and hence, the process of corrosion decreases increasing the life of tank and also saving the water.
Best of luck and keep learning and be growing.
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