NCERT Solutions for class 10th Science Chapter 3 Metals and Non-Metals

NCERT Intex Questions

Question 1. Give example of a metal which
(a) is liquid at room temperature.
(b) can be easily cut with knife.
(c) is the best conductor of heat.
(d) is the poorest conductor of heat.

Sol. (a) Mercury (Hg). Metals are solids at room temperature, except mercury which is a liquid because mercury atoms won’t combine with each other to form a lattice structure, to become a solid.
(b) Sodium (Na). Sodium is an alkali metal. Due to the presence of weak metallic bonding alkali metals are soft and can be cut with a knife.
(c) Silver (Ag). Silver is the best conductor of heat because its electrons are free to move than those of the other elements. The more free electrons in a metal, the greater its conductivity.
(d) Lead (Pb). Metals are generally good conductors of heat but lead and mercury are metals that have the least conductivity of heat.

Question 2. Explain the meaning of malleable and ductile.

Sol. Malleability and ductility are the properties of metals that help them to deform.
•Malleable: The property by virtue of which a substance is capable of deforming under pressure and can be beaten into sheets is known as malleability. A substance that shows the property of malleability is known as a malleable substance. Metals are malleable in nature, e.g., gold and silver.
•Ductile: The property by virtue of which a substance can be drawn into wires is known as ductility. A substance that shows the property of ductility is known as ductile. Gold is the most ductile metal.

Question 3. Why is sodium kept immersed in kerosene oil?

Sol. Sodium is a very reactive metal so it reacts vigorously with the oxygen of air and catches fire. It is kept immersed in kerosene oil to protect it from the action of oxygen, moisture and carbon dioxide of air and to prevent accidental fires.

Question 4. Write the equations for the reactions of
(a) iron with steam
(b) calcium with water
(c) potassium with water

Sol. (a) Iron reacts with steam to form metal oxide and hydrogen.

(b) Calcium react with water to form calcium hydroxide and liberates hydrogen gas

Note: The reaction of calcium with water is exothermic but the heat evolved is not sufficient for the hydrogen to catch fire.
(c) Potassium reacts with water to form potassium hydroxide and liberates hydrogen gas.

Note: Potassium reacts violently with cold water and its reaction is so violent and exother­ mic that the evolved hydrogen immediately catches fire.

Question 5. 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 to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal ?
(ii) What would you observe
when Bis is added to solution of copper (II) sulphate?
(iii) Arrange the metals A, B, C and D in order of increasing reactivity.

Sol. In the reactivity series, we find that order of reactivity of metals present in the salt solutions is Zn> Fe> Cu> Ag. Thus, based on the information given in the table, it can be concluded that:
Metal A is more reactive than copper as it displaces copper from copper
(II) sulphate and is less reactive than iron as it fails to displace iron from iron (II) sulphate.
Metal B is more reactive than iron and less reactive than zinc.
Metal C is more reactive than silver and less reactive than other metals i.e. Fe, Cu and Zn.
Metal Dis least reactive. Thus,
(i) The most reactive metal is B.
(ii) Since B is more reactive than iron so it is also more reactive than copper hence it will displace copper from copper (II) sulphate solution. The blue colour of copper (II) sulphate solution will slowly fade.
(iii) The arrangement of metals A, B, C and D in decreasing order of reactivity is B>A>C>D.

Question 6. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4

Sol. When a metal reacts with dilute hydrochloric acid, the gas produced is hydrogen ( H2).
Iron and dilute H2S04 react to produce H2 as under the given reaction:

Question 7. What would you observe when zinc is added to a solution of iron (II) sulphate? Write chemical equation that takes place.

Sol. When zinc is added to the solution of iron sulphate, the colour of iron sulphate solution changes. It is because zinc is more reactive than iron, therefore, it displaces iron from its solution of iron sulphate and a grey precipitate ofiron and a colourless/white solution of zinc sulphate is formed.

Question 8. (i) Write electron-dot structures for sodium, magnesium and oxygen.
(ii) Show the formation of Na2O and MgO by transfer of electrons.
(iii) What are the ions present in these compounds?

(iii) The ions present in Nap are Na+and 02- i.e. sodium ion (Na+) and oxide ion (02-) and the ions present in Mg0 are Mg2+and 02- i.e. magnesium ion (Mg2+) and oxide ions (02-).

Question 9. Why do ionic compounds have high melting points?

Sol. In an ionic compound there is large electrostatic force of attraction between opposite charged ions. To overcome these forces, a considerable amount of energy is needed therefore ionic compounds have high melting points.

Question 10. Define the following terms.
(i) Minerals (ii) Ores (iii) Gangue

Sol. (i) Minerals: The elements or compounds, which occur naturally in earth’s crust, are known as minerals.
(ii) Ores: These are those minerals which contains a high percentage of a metal i.e., the mineral from which a metal can be profitably extracted.
(iii) Gangue: The unwanted rocky, earthy or sandy materials which are associated with ores as impurities are called gangue or matrix.

Question 11. Name two metals which are found in nature in the free state.

Sol. The metals at the bottom of the reactivity series are mostly found in a free state. Gold (Au) and Platinum (Pt) are two metals that are found in the free state of nature.
Note: Apart from gold and platinum, silver and copper are also found in the free state.

Question 12. What chemical process is used for obtaining a metal from its oxide?

Sol. 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.

Question 13. Metallic oxides of zinc, magnesium and copper were heated with the following metals.

In which case the displacement reaction taking place?

Sol. From the reactivity series we find the order of reactivity of Zn, Mg and Cu as,
Mg>Zn>Cu
i.e., magnesium is the most reactive and so it will displace zinc from zinc oxide and copper from copper oxide

Zinc is less reactive than magnesium so it will not displace magnesium from magnesium oxide.

Zinc is more reactive than copper so it will displace copper from copper oxide.

Since copper is least reactive it will neither displace Mg nor Zn from their
oxides.

So, on the basis of reactivity series of metals the displacement reaction will take place as follows:

Question14. Which metals do not corrode easily?

Sol. Au (Gold) and Pt (Platinum) are placed near the bottom of the activity series, hence have the least reactivity and do not corrode easily.

Question 15. What are alloys?

Sol. Alloys are homogeneous mixtures of more than one metal or even metals and non-metals. It is obtained by first melting the primary metal and then dissolving the other elements in it in a definite proportion. It is then cooled at room temperature. An example of the alloy is brass which is made up of copper and zinc.

Exercise:

Question1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgC12 solution and aluminium metal
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper metal

Sol. (d) Since copper is more reactive than silver, so, copper will displace silver from silver nitrate solution.

Question 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 coat of zinc (d)All of the above

Sol. (c) Applying a coat of zinc on iron pan to prevent it from rusting, is called galvanization. We can also apply grease and paint to prevent iron from rusting. However, in case ofiron 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.

Question 3. An element can react with oxygen to give a compound with high melting point. This compound is also soluble in water. The element is likely to be
(a) Calcium (b) Carbon
(c) Silicon (d) Iron

Sol. (a) Calcium (Ca) combines with oxygen to form calcium oxide (CaO) which has a high melting point and dissolves in water to form Ca(OH)2.

Question 4. Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin.
(b) zinc has higher melting point than tin.
(c) zinc in more reactive than tin.
(d) zinc is less reactive than tin
.

Sol. (c) Zinc is more reactive than tin (zinc is above tin in reactivity series) so it will react with organic acids (present in food) to form poisonous compounds. To avoid this, food cans are coated with tin and not with zinc.

Question 5. You are given a hammer, a battery, a bulb, wire 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.

Sol. (a) With the hammer, we can beat the sample and ifit can be beaten into thin sheets (i.e., 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 as these are based on the physical properties. No chemical reactions are involved in these tests.

Question 6. What are amphoteric oxides? Give examples of two amphoteric oxides.

Sol. Amphoteric oxides: Those oxides which can act both as an acid and a base are known as an amphoteric oxides.
Examples: Aluminium oxide (Alp3) and zinc oxide (ZnO).

Question7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Sol. Sodium and calcium can displace hydrogen from dilute acids as they lie above hydrogen in the reactivity series and are more reactive than hydrogen.
Copper and silver can not displace hydrogen from dilute acids as they lie below hydrogen in the reactivity series and are less reactive than hydrogen.

Question 8. In the electrolytic refining of a metal (M), what would you take as the anode, the cathode and the electrolyte?

Sol. Anode : It is a rod or wire of impure metal M.
Cathode : It is a rod or wire of pure metal M.
Electrolyte : It is an aqueous solution of a soluble salt of the metal M.

Question 9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas 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.

Sol. (a) Sulphur is a non-metal, on burning it will be converted into its oxide. Oxides of non-metals are acidic. Therefore in this case, sulphur dioxide produced will be acidic.
(i) There will be no action of the gas on dry litmus paper.
(ii) Wet litmus paper will tum to red.
(b) The balanced chemical equation can be written as under:

Question 10. State two ways to prevent rusting of iron.

Sol. Two ways to prevent the rusting of iron are as follows:
(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.
Note: The process of rusting is a combustion reaction, similar to burning. Left in contact with oxygen, iron will react with the oxygen to form rust. Unlike burning, though, the reaction is much slower and does not create a flame.

Question11. What type of oxides are formed when non-metals combine with oxygen?

Sol. When non-metals combine with oxygen the oxides formed are either acidic or neutral. For example

Question 12. Give reasons:
(a) Platinum, silver and gold 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.

Sol. (a) Platinum, gold and silver are used to make jewellery because they are very lustrous. Also, they are very less reactive and do not corrode easily.
(b) Sodium, potassium and lithium react with water (or moisture in air) producing a lot of heat along with evolution of hydrogen. As a result the hydrogen gas evolved, catches fire. To avoid this, these metals are not kept in air but are kept under kerosene oil (to avoid contact with air and water).
(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 utensils for cooking.
(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 since oxides are easier to reduce than sulphides and carbonates.

Question 13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in clearing vessels.

Sol. 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 basic copper carbonate and dissolves the layer. That is the reason why tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.

Question 14. Differentiate between metals and non-metals on the basis of their chemical properties.

Sol. Differences in chemical properties of metals and non-metals

Question 15. A man went door to door posing as 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 has used?

Sol. The man has used an aqua-regia solution (mixture of cone. HCl and cone.
HN03 in the ratio of 3 : 1 by volume). Gold dissolves in aqua-regia and forms gold (III) chloride, AuCliauric chloride). Since gold actually reacted with aqua-regia so a loss in mass of gold bangles occurred. Since, the dull layer of
gold was removed from its surface so there was original shine on the bangles.

Note: Aqua regia consists of 3 parts HCl to i part HN03. it is an excellent oxidant, which can dissolve gold and platinum. it produces yellow fumes from the reaction of HCl and HN03 to produce nitrosyl chloride, (NOC!), chlorine gas, (Cl) and water
(H2O).

Question 16. Give reason why copper is used to make hot water tanks and not steel (an alloy of iron).

Sol. Copper is used to make hot water tanks and not steel, this is because the iron (in steel) is more reactive than copper, it react with hot steam to produce ferrosoferric oxide. Due to which the body of tank will become weaker and weaker. On other hand, copper does not react with hot water.

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