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Metal and Non-Metals: Class 10 Science answers, notes
Get summaries, questions, answers, solutions, notes, extras, PDF and guides for Chapter 3 Metals and Non-Metals: Class 10 Science textbook, which is part of the syllabus for students studying under SEBA (Assam Board), NBSE (Nagaland Board), TBSE (Tripura Board), CBSE (Central Board), MBOSE (Meghalaya Board), BSEM (Manipur Board), WBBSE (West Bengal Board), and all other boards following the NCERT books. These solutions, however, should only be treated as references and can be modified/changed.
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Summary
Elements can be sorted into metals and non-metals based on their features. Metals usually have a shiny look, called metallic lustre, and are generally hard. Sodium is an exception, being soft. Metals can be hammered into thin sheets; this is called malleability. They can also be stretched into wires, a property known as ductility. Gold is very malleable and ductile. Metals are good at letting heat and electricity pass through them. This is why pots are made of metal and electrical wires are made of copper. When hit, metals often make a ringing sound, a feature called sonority.
Non-metals, like carbon or sulphur, mostly have features opposite to metals. They are usually not shiny, though iodine is an exception. They are not malleable or ductile. They are poor conductors of heat and electricity, though graphite, a form of carbon, is an exception. Most non-metals are solids or gases at room temperature; bromine is a liquid non-metal.
Metals react with oxygen in the air to form metal oxides. These oxides are usually basic in nature. Some metal oxides, like those of aluminium and zinc, can behave as both acidic and basic; these are called amphoteric oxides. Non-metals react with oxygen to form non-metal oxides, which are usually acidic. Metals show different levels of eagerness to react. Some, like potassium and sodium, react very strongly with oxygen and water, so they are stored in kerosene oil. Iron rusts when it is exposed to both air and water. Gold is very unreactive. This order of reactivity is shown in a list called the reactivity series. A more reactive metal can push a less reactive metal out of its salt solution.
Metals and non-metals can react with each other by transferring tiny particles called electrons. When a metal loses electrons, it becomes a positively charged ion. When a non-metal gains electrons, it becomes a negatively charged ion. These oppositely charged ions attract each other strongly, forming an ionic compound, like common salt, which is sodium chloride. Ionic compounds are usually solid and hard. They have high melting and boiling points. They often dissolve in water and can conduct electricity when melted or dissolved in water, because their ions can move freely.
Metals are found in the Earth’s crust as minerals. If a mineral contains a lot of a particular metal that can be taken out easily, it is called an ore. The process of getting metals from their ores is called metallurgy. This involves several steps: first, concentrating the ore by removing impurities called gangue; then, extracting the metal; and finally, refining it to get a pure metal. The method of extraction depends on how reactive the metal is. Very reactive metals are often extracted by passing electricity through their molten compounds. Moderately reactive metals are often obtained by heating their oxides with carbon. Some less reactive metals can be obtained just by heating their ores. Refining often uses electrolysis to get very pure metals.
Corrosion is when metals get damaged by reacting with their surroundings, like the rusting of iron. This can be prevented by methods like painting, oiling, galvanising (which is coating with zinc), or by making alloys. An alloy is a mixture of a metal with other metals or non-metals. Alloys often have improved properties compared to pure metals. For example, pure iron is soft, but steel, an alloy of iron and carbon, is hard and strong. Stainless steel, an alloy containing chromium, does not rust. Pure gold is very soft, so it is alloyed with copper or silver to make it harder for jewellery.
Textbook solutions
Intext Questions and Answers I
1. Give an example of a metal which
(i) is a liquid at room temperature.
Answer: An example of a metal which is a liquid at room temperature is mercury. All metals except mercury exist as solids at room temperature.
(ii) can be easily cut with a knife.
Answer: An example of a metal which can be easily cut with a knife is sodium. Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife.
(iii) is the best conductor of heat.
Answer: An example of a metal which is the best conductor of heat is silver. The best conductors of heat are silver and copper.
(iv) is a poor conductor of heat.
Answer: An example of a metal which is a poor conductor of heat is lead. Lead and mercury are comparatively poor conductors of heat.
2. Explain the meanings of malleable and ductile.
Answer: Malleability is the property where some metals can be beaten into thin sheets. Ductility is the ability of metals to be drawn into thin wires.
Intext Questions and Answers II
1. Why is sodium kept immersed in kerosene oil?
Answer: Sodium is kept immersed in kerosene oil because metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.
2. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
Answer: (i) The equation for the reaction of iron with steam is:
3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
(ii) The equation for the reaction of calcium with water is:
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
The equation for the reaction of potassium with water is:
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.
| Metal | Iron(II) Sulphate | Copper (II) Sulphate | Zinc Sulphate | Silver Nitrate |
|---|---|---|---|---|
| A | No reaction | Displacement | — | — |
| B | Displacement | — | No reaction | — |
| 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.
Answer: (i) Metal B is the most reactive metal. This is determined from the table because metal B displaces iron from Iron(II) sulphate, whereas metals A, C, and D do not show this reaction, indicating they are less reactive than iron or B.
(ii) If metal B is added to a solution of Copper(II) sulphate, a displacement reaction would be observed where metal B displaces copper from the Copper(II) sulphate solution. This inference is based on the table showing metal B displaces iron from Iron(II) sulphate (making B more reactive than iron), and the general activity series which indicates iron is more reactive than copper. Therefore, metal B is also more reactive than copper.
(iii) The metals A, B, C, and D arranged in the order of decreasing reactivity are B > A > C > D. This order is determined from their reactions in the table:
- Metal B is the most reactive as it displaces iron from Iron(II) sulphate.
- Metal A is less reactive than B (as it does not displace iron) but more reactive than copper, as it displaces copper from Copper(II) sulphate.
- Metal C is less reactive than A (as it does not displace iron or copper) but more reactive than silver, as it displaces silver from Silver nitrate.
- Metal D is the least reactive as it shows no reaction with any of the given salt solutions.
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: When dilute hydrochloric acid is added to a reactive metal, hydrogen gas is produced. This is because the general reaction is: Metal + Dilute acid → Salt + Hydrogen.
When iron reacts with dilute H₂SO₄, it produces a salt (iron(II) sulphate) and hydrogen gas. This reaction follows the general principle that metals react with acids to give a salt and hydrogen gas.
5. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Answer: When zinc is added to a solution of iron(II) sulphate, it would be observed that zinc displaces iron from the iron(II) sulphate solution. This occurs because zinc is more reactive than iron, as indicated in the activity series. Consequently, solid iron metal would be deposited, and zinc would dissolve to form zinc sulphate solution.
The chemical reaction that takes place is a displacement reaction where zinc reacts with iron(II) sulphate to form zinc sulphate and iron. This follows the general pattern for such reactions: Metal A + Salt solution of B → Salt solution of A + Metal B, where Metal A (zinc) is more reactive than Metal B (iron).
Intext Questions and Answers III
1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
Answer: The electronic configurations for sodium, oxygen, and magnesium are as follows:
Explanations:
- Sodium (Na) has an atomic number of 11 and an electronic configuration of K-2, L-8, M-1. Its electron-dot structure would show one valence electron.
- Oxygen (O) has an atomic number of 8 and an electronic configuration of K-2, L-6. Its electron-dot structure would show six valence electrons.
- Magnesium (Mg) has an atomic number of 12 and an electronic configuration of K-2, L-8, M-2. Its electron-dot structure would show two valence electrons.
(ii) Show the formation of Na₂O and MgO by the transfer of electrons.
Answer: The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds.
Explanations:
Formation of Na₂O (Sodium Oxide): A sodium atom (Na) has the electronic configuration 2,8,1. It loses the one electron from its M shell to achieve a stable octet in its L shell, becoming a sodium cation (Na⁺) with configuration 2,8.
Na (2,8,1) → Na⁺ (2,8) + e⁻
An oxygen atom (O) has the electronic configuration 2,6. It requires two more electrons to complete its octet in the L shell.
Therefore, for the formation of sodium oxide, two sodium atoms each transfer one electron to one oxygen atom. The oxygen atom, after gaining two electrons, gets a negative charge and forms an oxide anion (O²⁻) with configuration 2,8.
O (2,6) + 2e⁻ → O²⁻ (2,8)
The oppositely charged sodium ions (Na⁺) and oxide ion (O²⁻) are then held together by strong electrostatic forces of attraction to form sodium oxide (Na₂O).
Formation of MgO (Magnesium Oxide):
A magnesium atom (Mg) has the electronic configuration 2,8,2. It loses the two electrons from its M shell to achieve a stable octet, becoming a magnesium cation (Mg²⁺) with configuration 2,8.
Mg (2,8,2) → Mg²⁺ (2,8) + 2e⁻
An oxygen atom (O) has the electronic configuration 2,6 and requires two electrons to complete its octet.
For the formation of magnesium oxide, one magnesium atom transfers its two valence electrons to one oxygen atom. The oxygen atom, after gaining these two electrons, forms an oxide anion (O²⁻) with configuration 2,8.
O (2,6) + 2e⁻ → O²⁻ (2,8)
The oppositely charged magnesium ion (Mg²⁺) and oxide ion (O²⁻) are held together by strong electrostatic forces of attraction to form magnesium oxide (MgO).
(iii) What are the ions present in these compounds?
Answer:
- In Na₂O (sodium oxide), the ions present are sodium ions (Na⁺) and oxide ions (O²⁻).
- In MgO (magnesium oxide), the ions present are magnesium ions (Mg²⁺) and oxide ions (O²⁻).
2. Why do ionic compounds have high melting points?
Answer: Ionic compounds have high melting and boiling points. This is because a considerable amount of energy is required to break the strong inter-ionic attraction.
Intext Questions and Answers IV
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: Ores are minerals that, at some places, contain a very high percentage of a particular metal, and the metal can be profitably extracted from them.
(iii) Gangue: Gangue refers to the large amounts of impurities such as soil, sand, etc., with which ores mined from the earth are usually contaminated.
2. Name two metals which are found in nature in the free state.
Answer: Two metals which are found in nature in the free state are, for example, gold and silver.
3. What chemical process is used for obtaining a metal from its oxide?
Answer: The chemical process used for obtaining a metal from its oxide is reduction. For instance, the oxides of metals low in the activity series can be reduced to metals by heating alone. Metal oxides in the middle of the activity series are reduced to the corresponding metals by using suitable reducing agents such as carbon; for example, zinc oxide is reduced to metallic zinc when heated with carbon. Aluminium is obtained by the electrolytic reduction of aluminium oxide.
Intext Questions and Answers V
1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.
| Metal | Zinc | Magnesium | Copper |
| Zinc oxide | |||
| Magnesium oxide | |||
| Copper oxide |
In which cases will you find displacement reactions taking place?
Answer:
| Metal | Zinc | Magnesium | Copper |
| Zinc oxide | No reaction | Displacement | No reaction |
| Magnesium oxide | No reaction | No reaction | No reaction |
| Copper oxide | Displacement | Displacement | No reaction |
Explanation:
Reactive metals can displace less reactive metals from their compounds. The reactivity series indicates that magnesium is more reactive than zinc, and zinc is more reactive than copper. Therefore, displacement reactions will take place in the following cases:
- When zinc oxide is heated with magnesium.
- When copper oxide is heated with zinc.
- When copper oxide is heated with magnesium.
2. Which metals do not corrode easily?
Answer: The metals at the bottom of the activity series are the least reactive and are often found in a free state; these metals do not corrode easily. For example, gold, silver, and platinum are found in the free state. Silver and gold also do not react with oxygen even at high temperatures.
3. What are alloys?
Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. It is prepared by first melting the primary metal, and then, dissolving the other elements in it in definite proportions, after which it is then cooled to room temperature.
Exercise Questions and Answers
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: (d) AgNO₃ solution and copper metal.
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: (d) All of the above.
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
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.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer: Some metal oxides show both acidic as well as basic behaviour. Such metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. Two examples of amphoteric oxides are aluminium oxide and zinc oxide.
7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer: Metals above hydrogen in the activity series can displace hydrogen from dilute acids. Two metals which will displace hydrogen from dilute acids are magnesium and iron. Metals below hydrogen in the activity series do not displace hydrogen from dilute acids. Two metals which will not displace hydrogen from dilute acids are copper and silver.
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, the impure metal is made the anode and a thin strip of pure metal is made the cathode. A solution of the metal salt is used as an electrolyte.
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?
Answer: When the gas evolved from heating sulphur is tested:
(i) On dry litmus paper, there will be no action.
(ii) On moist litmus paper, blue litmus paper will turn red because non-metals form acidic oxides when they combine with oxygen, and these oxides dissolve in water to form acidic solutions.
(b) Write a balanced chemical equation for the reaction taking place.
Answer: A balanced chemical equation for the reaction taking place when sulphur is heated is S(s) + O₂(g) → SO₂(g).
10. State two ways to prevent the rusting of iron.
Answer: The rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys. Two ways to prevent the rusting of iron are painting and oiling.
11. What type of oxides are formed when non-metals combine with oxygen?
Answer: Non-metals form oxides which are either acidic or neutral.
12. Give reasons.
(a) Platinum, gold and silver are used to make jewellery.
Answer: Platinum, gold, and silver are used to make jewellery because they are metals of low reactivity and are often found in the free state. They are at the bottom of the activity series and do not react with oxygen even at high temperatures, nor do they react with water or dilute acids. Gold is also alloyed with either silver or copper to make it hard for making jewellery.
(b) Sodium, potassium and lithium are stored under oil.
Answer: Sodium, potassium, and lithium are stored under oil because they are highly reactive metals. Metals such as potassium and sodium react so vigorously with air that they catch fire if kept in the open. They also react violently with cold water, and the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
Answer: Aluminium is a highly reactive metal, high up in the activity series. However, at ordinary temperature, the surface of aluminium is covered with a thin layer of oxide. This protective oxide layer prevents the metal from further oxidation and makes it resistant to further corrosion, which allows it to be used for making utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Answer: Carbonate and sulphide ores are usually converted into oxides during the process of extraction because it is easier to obtain a metal from its oxide as compared to its sulphides and carbonates. Therefore, prior to reduction, the metal sulphides and carbonates must be converted into metal oxides through processes like roasting (for sulphides) and calcination (for carbonates)
13. Explain why these sour substances are effective in cleaning the vessels.
Answer: Tarnished copper vessels acquire a green coating of basic copper carbonate when they react with moist carbon dioxide in the air. Sour substances like lemon or tamarind juice contain acids. Acids react with basic copper carbonate to form salt and water, which helps in cleaning the vessels and restoring their shine………………
14. Differentiate between metal and non-metal on the basis of their chemical properties.
Answer: Metals combine with oxygen to form basic oxides, while non-metals form oxides which are either acidic or neutral. Metals react with dilute acids to give a salt and hydrogen gas, whereas non-metals do not displace hydrogen from dilute acids. Metals can form positive ions by losing electrons to non-metals, while non-metals form negatively charged ions by gaining electrons when reacting with metals.
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: A man posing as a goldsmith dipped gold bangles in a solution, which made them sparkle like new but reduced their weight drastically. Gold is a noble metal and is the least reactive metal, which does not react with water or most acids. However, aqua regia, which is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1, is a highly corrosive, fuming liquid that can dissolve gold, even though neither of these acids can do so alone. The goldsmith likely used aqua regia, which dissolved some of the gold from the bangles, causing the reduction in their weight.
16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer: Copper is used to make hot water tanks because metals such as copper do not react with water at all, even with hot water or steam. Iron, on the other hand, reacts with steam to form the metal oxide and hydrogen. Steel, being an alloy of iron, is also susceptible to rusting when exposed to moist air for a long period of time. Therefore, copper is preferred over steel for making hot water tanks due to its resistance to reaction with water and corrosion.
Extras
Additional MCQs (Knowledge Based)
1. A metal that is liquid at room temperature is:
A. Sodium
B. Mercury
C. Gallium
D. Bromine
Answer: B. Mercury
2. The property of metals by which they can be beaten into thin sheets is called:
A. Ductility
B. Malleability
C. Sonority
D. Lustre
Answer: B. Malleability
3. Which of the following metals is the most ductile?
A. Silver
B. Copper
C. Gold
D. Aluminium
Answer: C. Gold
4. Which of the following is NOT a physical property generally associated with metals?
A. Lustre
B. Good conductivity
C. Brittleness
D. Malleability
Answer: C. Brittleness
5. An element forms an oxide that turns red litmus blue. This element is most likely:
A. Sulphur
B. Carbon
C. Magnesium
D. Iodine
Answer: C. Magnesium
6. Aluminium oxide is an example of an ____________ oxide.
A. Acidic
B. Basic
C. Neutral
D. Amphoteric
Answer: D. Amphoteric
7. Sodium metal is kept immersed in:
A. Water
B. Alcohol
C. Kerosene
D. Sulphuric acid
Answer: C. Kerosene
8. Roasting : Sulphide ore :: Calcination : ____________.
A. Oxide ore
B. Carbonate ore
C. Halide ore
D. Native metal
Answer: B. Carbonate ore
9. Identify the metals that react with steam but not with cold or hot water.
P. Potassium
Q. Magnesium
R. Aluminium
S. Iron
A. P and Q
B. Q and R
C. R and S
D. P and S
Answer: C. R and S
10. Identify the metal that does not typically react with dilute hydrochloric acid.
A. Magnesium
B. Aluminium
C. Zinc
D. Copper
Answer: D. Copper
11. The process of forming a thick oxide layer on aluminium is known as:
A. Galvanisation
B. Anodising
C. Roasting
D. Alloying
Answer: B. Anodising
12. The reaction of iron(III) oxide with aluminium to produce molten iron is known as the:
A. Haber process
B. Thermit reaction
C. Contact process
D. Hall-Héroult process
Answer: B. Thermit reaction
13. Which method is used to extract highly reactive metals like sodium from their molten chlorides?
A. Reduction with carbon
B. Heating alone
C. Electrolytic reduction
D. Displacement by hydrogen
Answer: C. Electrolytic reduction
14. Which of the following is NOT a component of stainless steel?
A. Iron
B. Nickel
C. Chromium
D. Tin
Answer: D. Tin
15. An alloy of mercury with another metal is known as an ____________.
A. Amalgam
B. Emulsion
C. Ore
D. Gangue
Answer: A. Amalgam
16. Cinnabar is an ore of which metal?
A. Copper
B. Mercury
C. Lead
D. Zinc
Answer: B. Mercury
17. A non-metal exists as a liquid at room temperature. Identify it.
A. Carbon
B. Sulphur
C. Bromine
D. Iodine
Answer: C. Bromine
18. Which of the following are properties of ionic compounds?
P. Low melting points
Q. Conduct electricity in molten state
R. Soluble in kerosene
S. Generally brittle
A. P and R
B. Q and S
C. P and S
D. Q and R
Answer: B. Q and S
19. Identify the non-metal which is a good conductor of electricity.
A. Sulphur
B. Phosphorus
C. Graphite
D. Diamond
Answer: C. Graphite
20. Copper : Black oxide :: Magnesium : ____________ flame.
A. Yellow
B. Green
C. Dazzling white
D. Blue
Answer: C. Dazzling white
21. What is the common name for the impurities like soil and sand found in ores?
A. Mineral
B. Flux
C. Gangue
D. Slag
Answer: C. Gangue
22. A lustrous non-metal is:
A. Sulphur
B. Oxygen
C. Iodine
D. Nitrogen
Answer: C. Iodine
23. Which of these metals forms a protective oxide layer preventing further oxidation?
A. Sodium
B. Potassium
C. Aluminium
D. Gold
Answer: C. Aluminium
24. Which of the following metals is NOT found in its native state in significant amounts?
A. Gold
B. Silver
C. Platinum
D. Sodium
Answer: D. Sodium
25. The process of heating sulphide ores strongly in the presence of excess air is known as ____________.
A. Calcination
B. Roasting
C. Smelting
D. Leaching
Answer: B. Roasting
26. What is the composition of the alloy Solder?
A. Copper and Zinc
B. Copper and Tin
C. Lead and Tin
D. Iron and Chromium
Answer: C. Lead and Tin
27. During electrolytic refining of copper, the anode mud consists of:
A. Pure copper
B. Soluble impurities
C. Insoluble impurities
D. Copper sulphate
Answer: C. Insoluble impurities
28. Which of the following statements about alkali metals (e.g., sodium) are true?
P. They are hard
Q. They have low densities
R. They can be cut with a knife
S. They have high melting points
A. P and S
B. Q and R
C. P and Q
D. R and S
Answer: B. Q and R
29. Identify the metal that is a poor conductor of heat.
A. Silver
B. Copper
C. Aluminium
D. Lead
Answer: D. Lead
30. Metal oxide : Basic :: Non-metal oxide : ____________.
A. Basic
B. Acidic
C. Neutral
D. Amphoteric
Answer: B. Acidic
31. What is the approximate percentage of carbon in pure iron that makes it hard and strong?
A. 0.05%
B. 0.5%
C. 1.0%
D. 5.0%
Answer: A. 0.05%
32. The green coating formed on copper articles when exposed to moist air is:
A. Copper oxide
B. Copper sulphide
C. Basic copper carbonate
D. Copper nitrate
Answer: C. Basic copper carbonate
33. Which of these metals will melt if kept on your palm?
A. Sodium
B. Magnesium
C. Gallium
D. Aluminium
Answer: C. Gallium
34. Which of the following is NOT a method for preventing corrosion of iron?
A. Painting
B. Galvanising
C. Alloying
D. Heating strongly
Answer: D. Heating strongly
35. The reactivity series arranges metals in order of their decreasing ____________.
A. Density
B. Melting point
C. Activity
D. Abundance
Answer: C. Activity
36. What is the color of copper(II) oxide?
A. Red
B. Black
C. Green
D. White
Answer: B. Black
37. An element has an electronic configuration of 2, 8, 2. It will most likely:
A. Gain 2 electrons
B. Lose 2 electrons
C. Share 2 electrons
D. Lose 6 electrons
Answer: B. Lose 2 electrons
38. Aqua regia is a mixture of:
P. Concentrated HCl
Q. Dilute HCl
R. Concentrated HNO3
S. Dilute HNO3
A. P and S
B. Q and R
C. P and R
D. Q and S
Answer: C. P and R
39. Identify the metal that is extracted by reduction of its oxide with carbon.
A. Sodium
B. Potassium
C. Zinc
D. Aluminium
Answer: C. Zinc
40. 24 carat gold : Pure metal :: 22 carat gold : ____________.
A. Pure non-metal
B. Alloy
C. Compound
D. Ore
Answer: B. Alloy
41. What is the approximate length of wire that can be drawn from one gram of gold?
A. 200 m
B. 2 km
C. 20 km
D. 2 m
Answer: B. 2 km
42. The property of metals to produce a sound on striking a hard surface is called:
A. Malleability
B. Ductility
C. Sonority
D. Lustre
Answer: C. Sonority
43. Which of these non-metals is known for its hardness in one of its allotropic forms?
A. Sulphur
B. Phosphorus
C. Carbon
D. Oxygen
Answer: C. Carbon
44. Which of the following metals does NOT react with oxygen even at high temperatures?
A. Copper
B. Iron
C. Magnesium
D. Gold
Answer: D. Gold
45. During the electrolysis of molten sodium chloride, sodium is deposited at the ____________.
A. Anode
B. Cathode
C. Electrolyte
D. Salt bridge
Answer: B. Cathode
46. What is the main component of the alloy brass, besides copper?
A. Tin
B. Zinc
C. Lead
D. Nickel
Answer: B. Zinc
47. A metal M displaces iron from iron sulphate solution but is displaced by zinc from zinc sulphate solution. The correct order of reactivity (most to least) is:
A. Fe > M > Zn
B. Zn > M > Fe
C. M > Zn > Fe
D. Zn > Fe > M
Answer: B. Zn > M > Fe
48. Amphoteric oxides are those which react with:
P. Acids only Q. Bases only R. Both acids and bases S. Water to form alkalis
A. P only
B. Q only
C. R only
D. S only
Answer: C. R only
49. Identify the element that forms an acidic oxide.
A. Sodium
B. Magnesium
C. Aluminium
D. Sulphur
Answer: D. Sulphur
50. Sodium : 2,8,1 :: Chlorine : ____________.
A. 2,8,8
B. 2,8
C. 2,8,7
D. 2,7
Answer: C. 2,8,7
51. What is the approximate age of the ancient iron pillar located near the Qutub Minar in Delhi?
A. 1000 years
B. 1600 years
C. 2000 years
D. 2500 years
Answer: B. 1600 years
52. The black substance formed when silver articles react with sulphur in the air is:
A. Silver oxide
B. Silver carbonate
C. Silver sulphide
D. Silver nitrate
Answer: C. Silver sulphide
53. Which of these metals is commonly used as a coating in galvanisation to prevent rusting of iron?
A. Copper
B. Tin
C. Zinc
D. Aluminium
Answer: C. Zinc
54. Which of the following is NOT a characteristic of most ionic compounds?
A. High melting point
B. Soluble in water
C. Conduct electricity in solid state
D. Brittle nature
Answer: C. Conduct electricity in solid state
55. The process of heating carbonate ores strongly in a limited supply of air is called ____________.
A. Roasting
B. Calcination
C. Reduction
D. Smelting
Answer: B. Calcination
56. What is the height of the historic iron pillar in Delhi, known for its rust resistance?
A. 6 m
B. 8 m
C. 10 m
D. 12 m
Answer: B. 8 m
57. An element X forms an ion X²⁺. The atom of element X originally had:
A. 2 valence electrons
B. 6 valence electrons
C. 2 core electrons
D. 8 valence electrons
Answer: A. 2 valence electrons
58. Metals that are less reactive than hydrogen include:
P. Sodium Q. Magnesium R. Copper S. Gold
A. P and Q
B. Q and R
C. R and S
D. P and S
Answer: C. R and S
59. Identify the metal that reacts vigorously with cold water, producing hydrogen gas that catches fire.
A. Calcium
B. Magnesium
C. Sodium
D. Aluminium
Answer: C. Sodium
60. Bronze : Copper and Tin :: Brass : Copper and ____________.
A. Lead
B. Zinc
C. Nickel
D. Silver
Answer: B. Zinc
Additional MCQs (Competency Based)
1. Assertion (A): Metals like sodium and potassium are stored under kerosene.
Reason (R): These metals react vigorously with oxygen and moisture present in the air, potentially catching fire.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
2. Assertion (A): Ionic compounds generally have high melting and boiling points.
Reason (R): A considerable amount of energy is required to break the strong inter-ionic attraction between the oppositely charged ions.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
3. Assertion (A): Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
Reason (R): Aluminium forms a protective layer of aluminium oxide on its surface which prevents further corrosion and reaction.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
4. Assertion (A): Graphite, a non-metal, is a good conductor of electricity.
Reason (R): All non-metals are good conductors of electricity.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (c) A is true but R is false.
5. Assertion (A): During the electrolytic refining of copper, impure copper is made the cathode.
Reason (R): Pure copper gets deposited at the cathode from the electrolyte solution.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (d) A is false but R is true.
6. A student takes a piece of magnesium ribbon and burns it in the air. A white powder is formed. When this powder is dissolved in water and tested with litmus paper, what change is expected?
(a) Red litmus turns blue.
(b) Blue litmus turns red.
(c) No change in red litmus.
(d) No change in blue litmus.
Answer: (a) Red litmus turns blue.
7. An iron nail is placed in a solution of copper sulphate. After some time, the blue colour of the copper sulphate solution fades, and a reddish-brown coating is observed on the iron nail. This observation indicates that:
(a) Copper is more reactive than iron.
(b) Iron is more reactive than copper.
(c) Both iron and copper are equally reactive.
(d) No reaction has occurred.
Answer: (b) Iron is more reactive than copper.
8. A school bell is typically made of metal. When struck, it produces a clear, ringing sound. This characteristic property of metals is known as:
(a) Malleability
(b) Ductility
(c) Sonority
(d) Lustre
Answer: (c) Sonority
9. To prevent an iron frying pan from rusting, a common household practice is to apply a thin layer of oil after washing and drying it. This method works because the oil layer:
(a) Makes the iron surface harder.
(b) Reacts with iron to form a protective coating.
(c) Prevents direct contact of iron with air and moisture.
(d) Increases the electrical conductivity of iron.
Answer: (c) Prevents direct contact of iron with air and moisture.
10. A goldsmith is asked to make a very thin wire from a small lump of a precious metal. Which property of the metal is most crucial for this task?
(a) High density
(b) Ductility
(c) High melting point
(d) Sonority
Answer: (b) Ductility
11. Consider the statement: “Metals, in their pure state, have a shining surface. This property is called metallic lustre.”
If a piece of iron appears dull, what could be a reason, and how might its shine be restored according to common practice?
(a) It is an alloy; shine cannot be restored.
(b) It has reacted with atmospheric gases; cleaning its surface can restore shine.
(c) It is a non-metal; it will not shine.
(d) It needs to be melted and recast to shine.
Answer: (b) It has reacted with atmospheric gases; cleaning its surface can restore shine.
12. It is stated that “gold and silver are the most malleable metals.” What does this imply about their physical nature?
(a) They can be easily drawn into thin wires.
(b) They can be beaten into very thin sheets.
(c) They are very hard and brittle.
(d) They have very high melting points.
Answer: (b) They can be beaten into very thin sheets.
13. “The reaction of calcium with water is less violent. The heat evolved is not sufficient for the hydrogen to catch fire. Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.”
Based on this, why does calcium float when reacting with water?
(a) Calcium is less dense than water.
(b) The heat evolved makes the water boil vigorously.
(c) Hydrogen gas bubbles attach to calcium, making it buoyant.
(d) Calcium hydroxide formed is insoluble and floats.
Answer: (c) Hydrogen gas bubbles attach to calcium, making it buoyant.
14. Match the metal in Column A with its characteristic property or use in Column B.
| Column A (Metal) | Column B (Characteristic/Use) |
| (i) Mercury | 1. Used for making jewellery, very ductile |
| (ii) Sodium | 2. Forms a protective oxide layer, used in aircraft parts |
| (iii) Gold | 3. Liquid at room temperature |
| (iv) Aluminium | 4. Soft, can be cut with a knife, stored in kerosene |
Codes:
(a) (i)-3, (ii)-4, (iii)-1, (iv)-2
(b) (i)-1, (ii)-2, (iii)-3, (iv)-4
(c) (i)-3, (ii)-1, (iii)-4, (iv)-2
(d) (i)-4, (ii)-3, (iii)-2, (iv)-1
Answer: (a) (i)-3, (ii)-4, (iii)-1, (iv)-2
15. Match the metallurgical process in Column A with its description in Column B.
| Column A (Process) | Column B (Description) |
| (i) Roasting | 1. Heating carbonate ores strongly in limited air |
| (ii) Calcination | 2. Purifying impure metals using electricity |
| (iii) Electrolytic refining | 3. Coating iron with a layer of zinc |
| (iv) Galvanisation | 4. Heating sulphide ores strongly in the presence of excess air |
Codes:
(a) (i)-1, (ii)-4, (iii)-2, (iv)-3
(b) (i)-4, (ii)-1, (iii)-2, (iv)-3
(c) (i)-4, (ii)-1, (iii)-3, (iv)-2
(d) (i)-1, (ii)-2, (iii)-4, (iv)-3
Answer: (b) (i)-4, (ii)-1, (iii)-2, (iv)-3
16. Arrange the following metals in decreasing order of their reactivity with oxygen: Sodium (Na), Copper (Cu), Magnesium (Mg), Iron (Fe).
(a) Na > Mg > Fe > Cu
(b) Cu > Fe > Mg > Na
(c) Mg > Na > Cu > Fe
(d) Fe > Cu > Na > Mg
Answer: (a) Na > Mg > Fe > Cu
17. The extraction of a moderately reactive metal like zinc from its sulphide ore (ZnS) involves several steps. Arrange the following general steps in the correct sequence:
(I) Reduction of the metal oxide to metal.
(II) Roasting of the sulphide ore to convert it into metal oxide.
(III) Concentration of the ore.
(IV) Refining of the impure metal.
(a) III → I → II → IV
(b) II → III → I → IV
(c) III → II → I → IV
(d) I → II → III → IV
Answer: (c) III → II → I → IV
18. A solution named ‘aqua regia’ is prepared by mixing concentrated hydrochloric acid and concentrated nitric acid. If these acids are mixed in a volume ratio of 3:1 respectively, what volume of concentrated nitric acid would be present in 80 mL of aqua regia?
(a) 20 mL
(b) 30 mL
(c) 40 mL
(d) 60 mL
Answer: (a) 20 mL
19. The electronic configuration of element X is 2, 8, 2 and element Y is 2, 8, 7. When these elements react, what type of compound is likely to form and what will be its formula?
(a) Covalent compound, XY
(b) Ionic compound, XY₂
(c) Covalent compound, X₂Y
(d) Ionic compound, X₂Y₇
Answer: (b) Ionic compound, XY₂
20. A sample of an alloy used for making jewellery contains 22 parts pure gold and 2 parts copper. What is the carat value of this gold alloy?
(a) 2 parts
(b) 20 carat
(c) 22 carat
(d) 24 parts
Answer: (c) 22 carat
21. Consider the following statements regarding the properties of metals:
Statement 1: All metals exist as solids at room temperature.
Statement 2: Gallium and caesium have very low melting points and will melt if kept on your palm.
Which of the following is valid?
(a) Both Statement 1 and Statement 2 are true, and Statement 2 is the correct explanation for Statement 1.
(b) Both Statement 1 and Statement 2 are true, but Statement 2 contradicts Statement 1.
(c) Statement 1 is false, and Statement 2 is true.
(d) Statement 1 is true, and Statement 2 is false.
Answer: (c) Statement 1 is false, and Statement 2 is true.
22. Assertion (A): Anodising is a process that enhances the corrosion resistance of aluminium.
Reason (R): Anodising involves forming a thicker protective layer of aluminium oxide on the aluminium surface.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
23. A student sets up three test tubes.
Test tube A: Iron nails + tap water + air.
Test tube B: Iron nails + boiled distilled water + layer of oil.
Test tube C: Iron nails + anhydrous calcium chloride + corked.
After a few days, in which test tube(s) would rust be observed on the iron nails?
(a) Only in test tube A.
(b) Only in test tube B.
(c) Only in test tube C.
(d) In both test tubes A and B.
Answer: (a) Only in test tube A.
24. Match the alloy in Column A with its constituent metals in Column B.
| Column A (Alloy) | Column B (Constituent Metals) |
| (i) Brass | 1. Lead and Tin |
| (ii) Bronze | 2. Copper and Tin |
| (iii) Solder | 3. Copper and Zinc |
| (iv) Amalgam | 4. Mercury and another metal |
Codes:
(a) (i)-3, (ii)-2, (iii)-1, (iv)-4
(b) (i)-2, (ii)-3, (iii)-4, (iv)-1
(c) (i)-3, (ii)-1, (iii)-2, (iv)-4
(d) (i)-1, (ii)-4, (iii)-3, (iv)-2
Answer: (a) (i)-3, (ii)-2, (iii)-1, (iv)-4
25. “Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO₃ is a strong oxidising agent. It oxidises the H₂ produced to water and itself gets reduced…”
However, which two metals are exceptions that can react with very dilute HNO₃ to evolve H₂ gas?
(a) Copper and Silver
(b) Magnesium and Manganese
(c) Aluminium and Zinc
(d) Gold and Platinum
Answer: (b) Magnesium and Manganese
Additional Questions and Answers
1. What is metallic lustre?
Answer: Metals, in their pure state, have a shining surface. This property is called metallic lustre.
2. What is malleability?
Answer: The property by which some metals can be beaten into thin sheets is called malleability.
3. What is ductility?
Answer: The ability of metals to be drawn into thin wires is called ductility.
4. What is sonority?
Answer: Sonority is the property of metals that produce a sound on striking a hard surface; such metals are said to be sonorous.
5. Which metals can be cut with a knife?
Answer: Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. Sodium metal can also be cut with a knife.
6. Which property of metals makes them suitable for cooking vessels?
Answer: Metals are good conductors of heat and have high melting points, which makes them suitable for cooking vessels.
7. Which two metals melt when held in the palm of the hand?
Answer: Gallium and caesium have very low melting points and these two metals will melt if you keep them on your palm.
8. Name a non-metal that is liquid at room temperature.
Answer: Bromine is a non-metal which is a liquid at room temperature.
9. What is an allotrope?
Answer: Carbon is a non-metal that can exist in different forms. Each form is called an allotrope.
10. an example of an allotrope of carbon that conducts electricity.?
Answer: Graphite, an allotrope of carbon, is a conductor of electricity.
11. What characterises an amphoteric oxide?
Answer: Amphoteric oxides are metal oxides, such as aluminium oxide and zinc oxide, which show both acidic as well as basic behaviour. Such metal oxides react with both acids as well as bases to produce salts and water.
12. What are electrovalent compounds?
Answer: The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds.
13. Why do solid electrovalent compounds not conduct electricity?
Answer: Electrovalent compounds (ionic compounds) in the solid state do not conduct electricity because movement of ions in the solid is not possible due to their rigid structure.
14. Why do molten electrovalent compounds conduct electricity?
Answer: Electrovalent compounds (ionic compounds) conduct electricity in the molten state. This is possible in the molten state since the electrostatic forces of attraction between the oppositely charged ions are overcome due to the heat. Thus, the ions move freely and conduct electricity.
15. What is metallurgy?
Answer: The extraction of metals from their ores and then refining them for use is known as metallurgy.
16. What term is used for unwanted materials like soil and sand associated with ores?
Answer: Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue.
17. What is galvanisation?
Answer: Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
18. What is anodising?
Answer: Anodising is a process of forming a thick oxide layer of aluminium.
19. Why is sodium stored under kerosene oil?
Answer: Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.
20. What is an alloy?
Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
21. What is the thermit reaction?
Answer: The reaction of iron(III) oxide (Fe₂O₃) with aluminium, which is used to join railway tracks or cracked machine parts, is known as the thermit reaction.
22. Explain how metals react with water, giving examples for reactions with cold water, hot water and steam.
Answer: Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. However, all metals do not react with water.
- Reaction with cold water:
- Metals like potassium and sodium react violently with cold water. In the case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.
2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) + heat energy
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + heat energy - The reaction of calcium with water is less violent. The heat evolved is not sufficient for the hydrogen to catch fire.
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.
- Metals like potassium and sodium react violently with cold water. In the case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.
- Reaction with hot water:
- Magnesium does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen. It also starts floating due to the bubbles of hydrogen gas sticking to its surface.
- Reaction with steam:
- Metals like aluminium, iron and zinc do not react either with cold or hot water. But they react with steam to form the metal oxide and hydrogen.
2Al(s) + 3H₂O(g) → Al₂O₃(s) + 3H₂(g)
3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
- Metals like aluminium, iron and zinc do not react either with cold or hot water. But they react with steam to form the metal oxide and hydrogen.
- No reaction with water:
- Metals such as lead, copper, silver and gold do not react with water at all.
23. Describe the reactivity series and explain how it helps predict which metal will displace another from its salt solution.
Answer: The reactivity series is a list of metals arranged in the order of their decreasing activities. After performing displacement experiments, the reactivity or activity series has been developed, as shown in Table 3.2.
Reactive metals can displace less reactive metals from their compounds in solution or molten form. It is simple and easy: if metal A displaces metal B from its solution, it is more reactive than B.
Metal A + Salt solution of B → Salt solution of A + Metal B.
Thus, the reactivity series helps predict displacement reactions by showing the relative reactivities of metals.
24. Outline the process of electrolytic refining of copper.
Answer: The most widely used method for refining impure metals is electrolytic refining. Many metals, such as copper, are refined electrolytically. In this process:
- The impure metal is made the anode.
- A thin strip of pure metal is made the cathode.
- A solution of the metal salt is used as an electrolyte. For copper, the electrolyte is a solution of acidified copper sulphate. The anode is impure copper, whereas the cathode is a strip of pure copper.
On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte. An equivalent amount of pure metal from the electrolyte is deposited on the cathode. On passing electric current, pure copper is deposited on the cathode.
The fate of impurities is as follows:
- The soluble impurities go into the solution.
- The insoluble impurities settle down at the bottom of the anode and are known as anode mud.
25. Explain the purposes of roasting and calcination in the extraction of metals from sulphide and carbonate ores.
Answer: It is easier to obtain a metal from its oxide, as compared to its sulphides and carbonates. Therefore, prior to reduction, the metal sulphides and carbonates must be converted into metal oxides.
- Roasting is the process where sulphide ores are converted into oxides by heating strongly in the presence of excess air. For example, in the roasting of zinc ores:
2ZnS(s) + 3O₂(g) —Heat→ 2ZnO(s) + 2SO₂(g) - Calcination is the process where carbonate ores are changed into oxides by heating strongly in limited air. For example, in the calcination of zinc ores:
ZnCO₃(s) —Heat→ ZnO(s) + CO₂(g)
The purpose of both processes is to convert sulphide or carbonate ores into metal oxides, which can then be reduced to the corresponding metals.
26. Discuss at least three methods used to prevent the corrosion of iron.
Answer: The rusting of iron can be prevented by several methods. Three such methods are:
- Painting, Oiling, or Greasing: These methods prevent rusting by creating a barrier between the iron surface and moist air. Iron rusts when exposed to moist air for a long time, so by applying paint, oil, or grease, the contact with air and water, which are necessary for rusting, is prevented.
- Galvanising: Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc. The galvanised article is protected against rusting because zinc is more reactive than iron and corrodes preferentially, or it forms a protective layer that prevents iron from being exposed to air and moisture. The article is protected even if the zinc coating is broken.
- Making alloys: Alloying is a very good method of improving the properties of a metal. For example, when iron is mixed with nickel and chromium, we get stainless steel, which is hard and does not rust. Thus, the alloy itself has properties that resist corrosion.
27. Describe the formation of ionic compounds by electron transfer and explain the nature of the bond.
Answer: The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds.
In the formation of magnesium chloride (MgCl₂), magnesium (Mg) is a metal and chlorine (Cl) is a non-metal.
- A magnesium atom has an electronic configuration of 2,8,2. It loses two electrons from its M shell to achieve a stable octet in its L shell, forming a magnesium cation (Mg²⁺):
Mg (2,8,2) → Mg²⁺ (2,8) + 2e⁻ - A chlorine atom has an electronic configuration of 2,8,7. It requires one more electron to complete its octet. Each of two chlorine atoms takes one electron from the magnesium atom to form chloride anions (Cl⁻):
Cl (2,8,7) + e⁻ → Cl⁻ (2,8,8)
The formation can be represented as:
Mg + 2Cl → [Mg]²⁺[Cl]⁻₂
The nature of the bond in ionic compounds like magnesium chloride is due to strong electrostatic forces of attraction. The oppositely charged ions, Mg²⁺ and Cl⁻, attract each other and are held by these strong forces. This strong force of attraction between the positive and negative ions results in the solid and somewhat hard nature of ionic compounds.
28. Explain the thermit reaction and its application in joining railway tracks.
Answer: The thermit reaction is a displacement reaction that is highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state. Specifically, the reaction of iron(III) oxide (Fe₂O₃) with aluminium is known as the thermit reaction.
This reaction is used to join railway tracks or cracked machine parts. The molten iron produced in the reaction fills the gaps or cracks, solidifying to create a strong joint.
The chemical equation involved is:
Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat
29. Outline the extraction of aluminium from its ore, emphasising the role of electrolysis in the process.
Answer: Aluminium is a metal high up in the activity series and is so reactive that it is never found in nature as a free element. Metals like aluminium cannot be obtained from their compounds by heating with carbon because these metals have more affinity for oxygen than carbon.
Aluminium is obtained by electrolytic reduction. Specifically, aluminium is obtained by the electrolytic reduction of aluminium oxide. In this process, the molten aluminium oxide is electrolysed. The metal (aluminium) is deposited at the cathode (the negatively charged electrode). This method is used for metals of high reactivity, where electrolysis of their molten ore yields the pure metal.
30. Discuss the differences in electrical conductivity between metals and non-metals.
Answer:
- Metals are generally good conductors of electricity. This property allows them to be used for making electric wires and circuits.
- Non-metals, on the other hand, generally have properties opposite to that of metals. They are typically bad conductors of heat and electricity.
However, there are exceptions. An example of a non-metal that conducts electricity is graphite. Graphite, which is an allotrope of carbon, is a conductor of electricity.
