Bihar Board Class 10 Science Solutions Chapter 3 Metals and Non-metals

BSEB Bihar Board Class 10 Science Solutions Chapter 3 Metals and Non-metals Textbook Questions and Answers.

Bihar Board Class 10 Science Solutions Chapter 3 Metals and Non-metals

Bihar Board Class 10 Science Chapter 3 Metals and Non-metals InText Questions and Answers

In-text Questions (Page 40)

Question 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 the poor conductor of heat.
Answer:
(i) Metal which is a liquid at room temperature is mercury.
(ii) Alkali metals such as lithium, sodium, potassium, etc. can be easily cut with a knife.
(iii) Metal which is the best conductor of heat is silver.
(iv) Metal which is the poorest conductor of heat is lead.

Question 2.
Explain the meanings of malleable and ductile.
Answer:
Malleable: Most of the metals can be beaten into sheets, therefore they are called malleable e.g., Al, Cu, Au, Ag are malleable.

Ductile: Most of the metals can be drawn into wires, therefore these metals are called ductile, e.g., Cu, Ag, Au, Pt are ductile.

In-text Questions (Page 46)

Question 1.
Why is sodium kept immersed in kerosene oil? [CBSE 2011]
Answer:
Sodium reacts both with air and water. It is a highly reactive metal. When kept in open, it readily combines with oxygen present in air to form its oxide. Similarly, it reacts with water vapour or moisture to form sodium hydroxide.
4Na(s) + O₂(g) → 2Na₂O(s)
\(2 \mathrm{Na}(s)+\underset{\text { (Moisture) }}{2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})} \longrightarrow 2 \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)\)
In order to preserve sodium metal, we generally keep it under kerosene so that neither air nor moisture may come in its contact.

Question 2.
Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water.
Answer:
(i) Iron reacts with steam to form magnetic oxide of iron and hydrogen gas.

(ii) Potassium reacts violently with cold water producing potassium hydroxide and hydrogen. The reaction is so exothermic that the hydrogen evolved immediately catches fire.

Calcium also reacts with cold water producing calcium hydroxide and hydrogen gas. The reaction of calcium with water is however less violent than that of potassium. The heat evolved is not sufficient for hydrogen to catch fire.

Question 3.
Samples of four metals A, B, C and D were taken and were added to the following solution one by one. The result obtained have been tabulated as follows:

Use the table given above to answer the following questions about metals A, B, C and D.
(a) Which is the most reactive metal?
(b) What would you observe when B is added to a solution of Copper (II) sulphate?
(c) Arrange the metals A, B, C and D in order of decreasing reactivity. [CBSE 2011]
Answer:
On the basis of the results given in the table

• Metal A is more reactive than copper and less reactive than iron.
• Metal B is more reactive than iron and less reactive than zinc.
• Metal C is only more reactive than silver and less reactive than other metals.
• Metal D is the least reactive in nature.

Thus, we can conclude that
(a) Metal B is the most reactive.
(b) Since B is more reactive than iron, it is also more reactive than copper. This means that it would displace copper from copper (II) sulphate solution. The blue colour of solution will slowly fade.
(c) The decreasing order of reactivity of metals is: B > A > C > D.

Question 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. [CBSE 2010]
Answer:
Hydrogen gas (H₂) is produced when a reactive metal reacts with dilute hydrochloric acid.
Iron and dilute H₂SO₄ react as follows:
Fe(s) + H₂SO₄(dil.) → FeSO₄(aq) + H₂(g)
Hydrogen gas is evolved in this reaction also.

Question 5.
What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place. [CBSE 2010]
Answer:
The solution becomes colourless due to formation of zinc sulphate and greyish black iron metal gets deposited.

In-text Questions (Page 49)

Question 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) (a) Atomic number (Z) of sodium (Na): 11.
Electronic distribution : K(2), L(8), M(1)

(b) Atomic number (Z) of oxygen (O): 8.
Electronic distribution : K(2), L(6)

(c) Atomic number (Z) of magnesium (Mg): 12.
Electronic distribution : K(2), L(8), M(2)

(ii) Formation of sodium oxide (Na₂O)

Formation of magnesium oxide (MgO)

(iii) In Na₂O, ions present are sodium cation (Na⁺) and oxide anion (O^2-);
In MgO, ions present are magnesium cation (Mg²⁺) and oxide anion (O^2-);

Question 2.
Why do ionic compounds have high melting points?
Answer:
It is due to strong electrostatic force of attraction between ions that form the compound.

In-text Questions (Page 53)

Question 1.
Define the following terms:
(i) Minerals (ii) Ore (iii) Gangue
Answer:
(i) Minerals: The naturally occurring chemical substance in form of which the metals occur in the Earth along with the impurities are called minerals.
(ii) Ore: The minerals from which the metal can be extracted conveniently and economically is called an ore.
(iii) Gangue: The earthy, sandy and rocky impurities associated with the mineral are called gangue or matrix.

Question 2.
Name two metals which are found in nature in the free state.
Answer:
Gold and platinum.

Question 3.
What chemical process is used for obtaining a metal from its oxide?
Answer:
Reduction.

In-text Questions (Page 55)

Question 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:
Relative positions of these metals in the activity series are : Mg, Zn, Cu : In the light of this: Magnesium (Mg) will displace both zinc (Zn) and copper (Cu) from their oxides.
Mg + ZnO → MgO + Zn
Mg + CuO → MgO + Cu
Zinc will displace copper from copper oxide.
Zn + CuO → ZnO + Cu
Copper is least reactive and will not initiate displacement reaction.

Question 2.
Which metals do not corrode easily?
Answer:
Metals such as gold (Au) and platinum (Pt) present at the bottom of the activity series do not corrode easily.

Question 3.
What are alloys?
Answer:
Alloys are homogeneous mixture of a metal with a metal or a non-metal.

Bihar Board Class 10 Science Chapter 3 Metals and Non-metals Textbook Questions and Answers

Question 1.
Which of the following pairs will give displacement reactions?
(а) NaCl solution and copper metal
(b) MgCl₂ solution and aluminium metal
(c) FeSO₄ solution and silver metal
(d) AgNO₃ solution and copper metal
Answer:
(d) AgNO₃ solution and copper metal

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 coating of zinc
(d) All of the above
Answer:
(c) Applying a coating of zinc

Question 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

Question 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) Food cans are coated with tin and not with zinc because zinc is more reactive than tin.

Question 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) With the help of hammer, convert both the metal and non-metal (solid) in the form of plates or rods. Metal will readily form thin plates when beaten since they are malleable. Non-metals being brittle will break when struck with the hammer. Now make a circuit in both the cases using metal plates, non-metal pieces, wires, bulb, battery and switch. Switch on the current. If the bulb glows, it means that the given samples are metals. In case, the bulb does not glow, it means that the samples are of non-metals.

(b) From these tests, we may conclude that

• metals are malleable while non-metals are not.
• metals are good conductors of electricity while non-metals are not (graphite is an exception).

Question 6.
What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer:
Those oxides which act as both acidic as well as basic are called amphoteric oxides, e.g. Al₂O₃ and ZnO are amphoteric oxides.

Question 7.
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer:
‘Zn’ and ‘Al’ will displace hydrogen from dilute acids because they are more reactive than hydrogen whereas Cu and Ag will not.

Question 8.
In the electrolytic refining of a metal ‘M’, what would you take as the anode, the cathode and the electrolyte? [NCERT Exampler]
Answer:
In the electrolytic refining of metal ‘M’, the impure metal ‘M’ acts as the anode, pure metal ‘M’ acts as the cathode while the soluble salt of metal ‘M’ acts as an electrolyte.

Question 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 below.

What will be the action of gas on
(i) dry litmus paper? (ii) moist litmus paper?
Write a balanced chemical equation for the reaction taking place. [CBSE 2011]
Answer:
The gas evolved upon heating sulphur powder on a spatula is sulphur dioxide.
\(\mathrm{S}(s)+\mathrm{O}_{2}(g) \stackrel{\text { Heat }}{\longrightarrow} \mathrm{SO}_{2}(g)\)
(i) SO₂(g) has no action of dry litmus paper.
(ii) SO₂(g) dissolves in moisture (water) present in moist litmus paper to form sulphurous acid. In acidic solution, moist litmus paper will change to red.

Question 10.
State two ways to prevent the rusting of iron.
Answer:
Two methods used to prevent the rusting of iron are:

1. 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.
2. Oiling, greasing or painting: The surface becomes waterproof by applying oil, grease or paint and moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.

Question 11.
What type of oxides are formed when non-metals combine with oxygen?
Answer:
Non-metals react with oxygen to form acidic oxides. For example,
(i) Carbon burns in air to form carbon dioxide (CO₂). It slightly dissolves in water to form carbonic acid (H₂CO₃) which turns blue litmus red.
C(s) + O₂(g) → CO₂(g)
\(\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \underset{\text { Carbonic acid }}{\mathrm{H}_{2} \mathrm{CO}_{3}(a q)}\)

(ii) Nitrogen burns in air to form nitrogen dioxide (NO₂). It dissolves in water in presence of air or oxygen to form nitric acid (HNO₃), which turns blue litmus red.
\(\mathrm{N}_{2}(g)+2 \mathrm{O}_{2}(g) \longrightarrow \underset{\text { Nitrogen dioxide }}{2 \mathrm{NO}_{2}(g)}\)
\(4 \mathrm{NO}_{2}(g)+\mathrm{O}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \underset{\text { Nitric acid }}{4 \mathrm{HNO}_{3}(a q)}\)
(iii) Sulphur burns in air to form SO₂ which dissolves in water to form sulphurous acid (H₂SO₃) which turns blue litmus red.

Question 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) These metals, placed at the bottom of the activity series, are unreactive in nature. Gold and platinum are known as noble metals. They are not affected by air, water and by chemicals. Since, they have bright lustre, jewellery can be made from these metals.

(b) Sodium, potassium and lithium are highly reactive metals which react vigorously with oxygen and water to evolve hydrogen gas. The reaction is violent and exothermic and so the evolved gas catches fire. Thus, to prevent its reactivity with oxygen and water, it is stored under oil.

(c) When exposed to air, the metal changes into its oxide called aluminium oxide (Al₂O₃). It gets deposited over the surface of the metal and forms a protective coating on the surface. Due to the presence of this layer, the metal becomes unreactive and can be used for making cooking utensils.

(d) It is because it is easier to reduce oxide ore as compared to carbonate and sulphide ores.

Question 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 vessel.
Answer:
Copper metal slowly reacts with water, carbon dioxide and oxygen present in air to form basic copper carbonate which is green in colour and gets deposited on the surface of the metal. Lemon juice and tamarind contain weak acids which reacts with basic copper carbonate to form soluble salts. The salts gets removed and the metal restores its shine.

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

1. Metals react with oxygen to form oxides which are basic in nature.
2. Active metals displace hydrogen from dilute acids.
3. Active metals displace hydrogen from water.
4. Metals are electropositive in nature (electron donors).

Non-metals

1. Non-metals react with oxygen to form oxides which are neutral or acidic.
2. Non-metals do not displace hydrogen from dilute acids.
3. Non-metals do not displace hydrogen from water.
4. Non-metals are electronegative in nature (electron acceptors).

Question 15.
A man went door to door posing to be 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:
The solution used by the man who claimed to be goldsmith was aqua regia or royal water. Aqua regia is a freshly prepared solution of concentrated hydrochloric acid and nitric acid in the ratio 3 : 1 by volume. Gold dissolves in aqua regia and hence, the weight of the bangles got reduced.

Question 16.
Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer:
Copper is a much better conductor of heat than steel. Although steel is much cheaper than copper, yet to save heat losses, hot water tanks are made up of copper rather than steel.

Bihar Board Class 10 Science Chapter 3 Metals and Non-metals Textbook Activities

Activity 3.1 (Textbook Page 37)

Observation: The surface of the metals (samples) is dull because they are covered with a layer of oxide, hydroxide, carbonate, etc. due to attack of gases and moisture of the air on their surface. On rubbing the surface with sand paper, this layer is removed and a shining surface appears.
Conclusion: Metals in the pure state (or freshly prepared or cut) have a shining surface.

Activity 3.2 (Textbook Page 37)

Observation and Conclusion: All the four metals (Fe, Cu, Al and Mg) cannot be cut with a knife. It means metals are hard. The ease with which the metals can be cut is found to be in the order Mg > Al > Cu > Fe. This exhibits that hardness varies from metal to metal. Sodium metal can be cut very easily with a knife since it is soft.

Activity 3.3 (Textbook Page 38)

Observation and Conclusion: It is observed that metals can be beaten into thin sheets, i.e., they are malleable.

Activity 3.4 (Textbook Page 38)

Observation and Conclusion: As wires of iron, copper and aluminium are easily available, this shows that metals can be drawn into wires, i.e., they are ductile.

Activity 3.5 (Textbook Page 38)

Observation and Conclusion: On heating the wire near the clamp, after some time the pin falls down. This shows that heat flows through the wire and melts the wax. Further the wire does not melt even after heating for a long time. This shows that metals have high melting points.

Activity 3.6 (Textbook Page 39)

Observation: The bulb glows. This indicates that electric current flows through the metal.
Conclusion: Metals are good conductors of electricity.

Activity 3.7 (Textbook Page 39)

Observation and Conclusion:

• Non-metals have no lustre (except iodine which has a lustre).
• Non-metals are soft and brittle.
• Non-metals are neither malleable nor ductile.
• Non-metals are non-conductors of electricity (except graphite).

Activity 3.8 (Textbook Page 40)

Observation:

• The solution obtained on dissolving ashes after burning magnesium turns red litmus blue.
• The solution obtained on dissolving gases from burning sulphur turns blue litmus red.

This shows that magnesium oxide (MgO) is basic while oxide of sulphur (SO₂) is acidic. The reactions are:
Mg + O₂ → 2MgO
S + O₂ → SO₂
Conclusion: Metal oxide are basic while non-metal oxides are acidic.

Activity 3.9 (Textbook Page 41)

Observation: Sodium burns with a brilliant yellow flame while magnesium burns with a dazzling white light. Both form white oxides, sodium oxide and magnesium oxide respectively, which are soluble in water. Aluminum does not bum but on heating in air forms white aluminum oxide (Al₂O₃). The metal forms an oxide even at ordinary temperature.

Zinc, red hot iron, lead and copper from oxides on strong heating. These oxides are insoluble in water. Zinc forms zinc oxides which is yellow when hot and white when cold. Iron forms iron (II) oxide and iron (III) oxide with a bright sparks. It is black in colour. Lead forms red lead (Pb₃O₄) when heated in air and copper forms black copper oxide.

The order, of reactivity with oxygen is:
Na > Mg > Al > Zn > Fe > Pb > Cu

At ordinary temperature, the surface of metals such as magnesium, aluminium, zinc and lead, etc. are covered with a thin layer of the oxide. The protection layer of the oxide prevents the metal from further oxidation. The surface needs to be cleaned with sand paper to remove to oxide layer before heating.

Conclusion: Generally all metals combine with oxygen to form metal oxides.
Metal + Oxygen → Metal oxide

Activity 3.10 (Textbook Page 42)

Observation:

• K, Na and Ca reacted with cold water, K and Na produced fire on water.
• Ca and Mg start floating after some time.
• Al, Fe and Zn reacted with steam.
• Pb and Cu did not react even with steam.

Conclusion: Order of reactivity of the given metals with water is: K > Na > Ca> Mg > Al > Zn > Fe > Pb > Cu.

Activity 3.11 (Textbook Page 44)

Observation: Mg reacts most vigorously followed by Al, Zn and then Fe. Lead and copper did not react at all. Temperature was found to rise in case of all the metals that reacted with dilute acid showing that reaction is exothermic. The rise of temperature is maximum in case of magnesium.
Conclusion: The order of reactivity with dilute HCl is : Mg > Al > Zn > Fe > Pb > Cu

Activity 3.12 (Textbook Page 45)

Observation: Reaction is found to occur in the tube containing iron wire dipped in copper sulphate solution. This is because in this tube, blue colour of copper sulphate solution fades and light green colour is seen due to the formation of iron (II) sulphate. Moreover, a brown deposit of copper is formed on the iron nail. Thus, the following reaction takes place:
Fe(s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

Conclusion: Iron is more reactive than copper and displaces copper from copper sulphate solution. In general a more reactive metal displaces a less reactive metal from its salt in the solution, hence it is a displacement reaction.

Activity 3.13 (Textbook Page 48)

Observation:
All the salts taken are solids. Each salt imparted a particular colour to the flame sodium salt burnt with a golden flame, potassium with a lilac flame and barium burnt with a pale green flame. The compounds did not melt on heating. The compounds were soluble in water but not in petrol or kerosene. The electric bulb glows on passing electric current. All these properties show that the compounds are ionic nature.

Conclusion:

• Ionic compounds are generally solids with high melting points.
• They impart a characteristic colour to the flame.
• They are soluble in a polar solvent like water and insoluble in non-polar solvents like kerosene, petrol, etc.
• Their aqueous solutions conduct electricity.

Activity 3.14 (Textbook Page 53)

Observation: It is observed that iron nails rust in test tube A but they do not rust in test tubes B and C. In test tube A, the nails are exposed to both air and water. In test tube B, the nails are exposed to water only and the nails in test tube C are exposed to dry air free from water vapour.
Conclusion: Presence of both air and moisture is essential for rusting to take place.