Metals and Non-metalsClass 10 Chemistry NCERT Solutions
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Q1E X E R C I S E S
Which of the following pairs will give displacement reactions?
(a)
NaCl solution and copper metal
(b)
solution and aluminium metal
(c)
solution and silver metal
(d)
solution and copper metal.
Solution
The correct answer is (d) solution and copper metal.
A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution. According to the reactivity series, copper is more reactive than silver.
- (a) Copper is less reactive than sodium.
- (b) Aluminium is less reactive than magnesium.
- (c) Silver is less reactive than iron.
- (d) Copper is more reactive than silver, so it will displace silver from the silver nitrate solution. The reaction is:
Q2E X E R C I S E S
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.
Solution
The correct answer is (c) Applying a coating of zinc.
While grease and paint can prevent rusting, they are not suitable for a frying pan because they would burn and contaminate the food when the pan is heated. Applying a coating of zinc (galvanisation) is a durable method that protects the iron from rust without being affected by the heat of cooking.
Q3E X E R C I S E S
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.
Solution
The correct answer is (a) calcium.
- Calcium is a metal that reacts with oxygen to form calcium oxide (), which is an ionic compound with a high melting point.
- Calcium oxide dissolves in water to form calcium hydroxide (), a base.
- Carbon and silicon are non-metals/metalloids whose oxides (, ) do not fit both criteria (e.g., has a low boiling point, is insoluble).
- Iron forms an oxide () with a high melting point, but it is insoluble in water.
Q4E X E R C I S E S
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.
Solution
The correct answer is (c) zinc is more reactive than tin.
Zinc is placed higher in the reactivity series than tin. If zinc were used to coat food cans, it would react with the acids present in the food, potentially contaminating it and making it unfit for consumption. Tin is less reactive and does not react with food contents, making it a safer choice for coating.
Q5E X E R C I S E S
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.
Solution
(a) Procedure to distinguish between metals and non-metals:
- Test for Malleability: Use the hammer to strike the given samples. If a sample can be beaten into a thin sheet, it is a metal. If it shatters or breaks into pieces, it is a non-metal (brittle).
- Test for Electrical Conductivity: Set up an electric circuit using the battery, bulb, wires, and switch. Place the sample into the circuit to complete it. If the bulb glows, the sample is a good conductor of electricity, indicating it is a metal. If the bulb does not glow, the sample is a poor conductor, indicating it is a non-metal.
(b) Usefulness of the tests:
These tests are generally useful because most metals are malleable and good conductors of electricity, while most non-metals are brittle and poor conductors. However, these tests are not completely definitive due to exceptions:
- Exceptions for Metals: Some metals like zinc can be brittle, and mercury is a liquid at room temperature.
- Exceptions for Non-metals: Graphite (an allotrope of carbon) is a good conductor of electricity. Iodine is lustrous. Therefore, while these physical property tests are a good first step, chemical properties provide a more reliable basis for classification.
Q6E X E R C I S E S
What are amphoteric oxides? Give two examples of amphoteric oxides.
Solution
Amphoteric oxides are metal oxides that show both acidic and basic behaviour. They react with both acids and bases to produce salt and water.
Two examples of amphoteric oxides are:
- Aluminium Oxide ()
- Zinc Oxide ()
Example reactions for Aluminium Oxide:
- Reaction with acid:
- Reaction with base:
Q7E X E R C I S E S
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Solution
Metals that are more reactive than hydrogen (above hydrogen in the activity series) can displace it from dilute acids. Metals less reactive than hydrogen (below it) cannot.
- Two metals that will displace hydrogen: Zinc (Zn) and Magnesium (Mg).
- Two metals that will not displace hydrogen: Copper (Cu) and Silver (Ag).
Q8E X E R C I S E S
In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Solution
In the electrolytic refining of a metal M:
- Anode: A thick block of the impure metal M is used as the anode (positive electrode).
- Cathode: A thin strip of the pure metal M is used as the cathode (negative electrode).
- Electrolyte: A water-soluble salt solution of the metal M (e.g., ) is used as the electrolyte.
Q9E X E R C I S E S
Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below. (a) What will be the action of gas on
(i)
dry litmus paper?
(ii)
moist litmus paper?
(b)
Write a balanced chemical equation for the reaction taking place.
Solution
When sulphur powder is heated, it reacts with oxygen to form sulphur dioxide () gas.
(a) Action on litmus paper:
(i)
Dry litmus paper: There will be no change in the colour of dry litmus paper. The acidic nature of a gas is exhibited only in the presence of water.
(ii)
Moist litmus paper: The sulphur dioxide gas will turn moist blue litmus paper to red. This is because reacts with the water on the litmus paper to form sulphurous acid ().
(b) Balanced chemical equation:
The reaction for the burning of sulphur in air is:
Q10E X E R C I S E S
State two ways to prevent the rusting of iron.
Solution
Two common ways to prevent the rusting of iron are:
- Painting or Oiling: Applying a layer of paint, oil, or grease on the surface of an iron object creates a barrier that prevents direct contact with air and moisture, thus stopping rust formation.
- Galvanisation: This is the process of coating iron or steel with a thin layer of zinc. Zinc is more reactive than iron, so it corrodes preferentially, protecting the iron underneath. This is known as sacrificial protection.
Q11E X E R C I S E S
What type of oxides are formed when non-metals combine with oxygen?
Solution
When non-metals combine with oxygen, they generally form acidic oxides. For example, carbon dioxide () and sulphur dioxide () dissolve in water to form carbonic acid and sulphurous acid, respectively. Some non-metals can also form neutral oxides, which are neither acidic nor basic, such as carbon monoxide (CO) and water ().
Q12E X E R C I S E S
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.
Solution
(a) Platinum, gold, and silver are used for making jewellery because they are highly lustrous (shiny), malleable, ductile, and most importantly, very unreactive. Their resistance to corrosion means they do not tarnish or react with air and moisture, allowing them to maintain their shine.
(b) Sodium, potassium, and lithium are highly reactive metals that react vigorously with oxygen and moisture in the air, often catching fire. To prevent these explosive reactions and ensure safe storage, they are kept immersed in an inert liquid like kerosene oil.
(c) Although aluminium is a highly reactive metal, its surface quickly forms a thin, tough, and non-porous protective layer of aluminium oxide () when exposed to air. This oxide layer is very stable and prevents the underlying metal from reacting further with air, water, or food. This property, along with it being lightweight and a good conductor of heat, makes it ideal for cooking utensils.
(d) It is easier and more economical to reduce a metal oxide to obtain the metal than it is to reduce a metal carbonate or sulphide. Therefore, during metallurgy, sulphide ores are converted to oxides by roasting (heating in excess air), and carbonate ores are converted to oxides by calcination (heating in limited air) before the final reduction step.
Q13E X E R C I S E S
You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Solution
Copper vessels become tarnished over time because copper reacts with moist carbon dioxide in the air, forming a green coating of basic copper carbonate (). This coating is basic in nature. Lemon and tamarind juice contain weak acids (citric acid and tartaric acid, respectively). These acids react with the basic copper carbonate layer in a neutralization reaction, forming a soluble salt that can be easily washed away with water. This process removes the dull green layer and restores the shiny, reddish-brown surface of the copper vessel.
Q14E X E R C I S E S
Differentiate between metal and non-metal on the basis of their chemical properties.
Solution
Here are the key chemical differences between metals and non-metals:
| Property | Metals | Non-metals |
|---|---|---|
| Nature of Oxides | They generally form basic oxides (e.g., ) or amphoteric oxides (e.g., ). | They generally form acidic oxides (e.g., ) or neutral oxides (e.g., CO). |
| Reaction with Dilute Acids | Most metals react with dilute acids to displace hydrogen gas and form a salt. | Non-metals do not react with dilute acids to displace hydrogen gas. |
| Reaction with Water | Reactive metals react with water or steam to produce a metal hydroxide or oxide and hydrogen gas. | Non-metals generally do not react with water or steam. |
| Ion Formation | They are electropositive; they tend to lose electrons to form positive ions (cations). | They are electronegative; they tend to gain electrons to form negative ions (anions). |
| Role in Reactions | They act as reducing agents because they donate electrons. | They act as oxidising agents because they accept electrons. |
Q15E X E R C I S E S
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?
Solution
The solution used by the fraudulent goldsmith was Aqua Regia.
Aqua Regia is a highly corrosive mixture of concentrated hydrochloric acid (HCl) and concentrated nitric acid (), typically in a 3:1 ratio. Gold is a very unreactive metal and does not dissolve in individual acids. However, it dissolves in Aqua Regia. When the man dipped the gold bangles into this solution, the outer, dull layer of gold dissolved, exposing the shiny layer underneath. This made the bangles sparkle, but it also removed a significant amount of gold from the surface, causing their weight to be drastically reduced.
Q16E X E R C I S E S
Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Solution
Copper is preferred over steel for making hot water tanks for two primary reasons:
- High Thermal Conductivity: Copper is an excellent conductor of heat. This allows for efficient transfer of heat to the water, making the heating process faster and more energy-efficient compared to steel.
- Corrosion Resistance: Copper is a relatively unreactive metal and does not react with hot water or steam. Steel, which is mostly iron, rusts (corrodes) when exposed to hot water and air for prolonged periods. This would weaken the tank over time and contaminate the water with rust.
Q1QUESTIONS (In-text, Set 1)
Give an example of a metal which
(i)
is a liquid at room temperature.
(ii)
can be easily cut with a knife.
(iii)
is the best conductor of heat.
(iv)
is a poor conductor of heat.
Solution
(i)
Mercury (Hg) is a metal that is a liquid at room temperature.
(ii)
Sodium (Na) and Potassium (K) are metals that are so soft they can be easily cut with a knife.
(iii)
Silver (Ag) is the best conductor of heat. Copper (Cu) is also an excellent conductor.
(iv)
Lead (Pb) and Mercury (Hg) are metals that are poor conductors of heat.
Q2QUESTIONS (In-text, Set 1)
Explain the meanings of malleable and ductile.
Solution
Malleable: This property describes the ability of a substance to be beaten or hammered into thin sheets without breaking. For example, gold and silver are highly malleable metals.
Ductile: This property describes the ability of a substance to be drawn into thin wires. Gold is the most ductile metal; one gram of gold can be drawn into a wire about 2 km long.
Q1QUESTIONS (In-text, Set 2)
(i) Write the electron-dot structures for sodium, oxygen and magnesium. (ii) Show the formation of Na_2O and…
(i)
Write the electron-dot structures for sodium, oxygen and magnesium.
(ii)
Show the formation of and by the transfer of electrons.
(iii)
What are the ions present in these compounds?
Solution
(i) Electron-dot structures:
- Sodium (Na, Atomic No. 11, Config: 2, 8, 1) has 1 valence electron. Its electron-dot structure is Na•
- Oxygen (O, Atomic No. 8, Config: 2, 6) has 6 valence electrons. Its electron-dot structure is :Ö: (with dots representing valence electrons).
- Magnesium (Mg, Atomic No. 12, Config: 2, 8, 2) has 2 valence electrons. Its electron-dot structure is •Mg• or Mg:
(ii) Formation by transfer of electrons:
- Formation of Sodium Oxide (): Two sodium atoms each transfer one valence electron to one oxygen atom. Sodium atoms form sodium ions (), and the oxygen atom forms an oxide ion ().
- Formation of Magnesium Oxide (): One magnesium atom transfers its two valence electrons to one oxygen atom. The magnesium atom forms a magnesium ion (), and the oxygen atom forms an oxide ion ().
(iii) Ions present:
- In Sodium Oxide (), the ions present are two Sodium ions () and one Oxide ion ().
- In Magnesium Oxide (), the ions present are one Magnesium ion () and one Oxide ion ().
Q2QUESTIONS (In-text, Set 2)
Why do ionic compounds have high melting points?
Solution
Ionic compounds are formed by strong electrostatic forces of attraction between positively charged ions (cations) and negatively charged ions (anions). A considerable amount of energy is required to overcome these strong inter-ionic forces and break the crystal lattice structure. Because of this, ionic compounds have high melting and boiling points.
Q1QUESTIONS (In-text, Set 3)
Define the following terms.
(i)
Mineral
(ii)
Ore
(iii)
Gangue
Solution
(i)
Mineral: A mineral is a naturally occurring element or compound found in the earth's crust.
(ii)
Ore: An ore is a type of mineral from which a metal can be extracted profitably and conveniently. For example, bauxite is an ore of aluminium.
(iii)
Gangue: Gangue refers to the undesirable impurities, such as soil, sand, and rock, that are mixed with an ore when it is mined from the earth.
Q2QUESTIONS (In-text, Set 3)
Name two metals which are found in nature in the free state.
Solution
Two metals that are found in nature in the free (or native) state are Gold (Au) and Platinum (Pt). This is because they are very unreactive and are located at the bottom of the activity series.
Q3QUESTIONS (In-text, Set 3)
What chemical process is used for obtaining a metal from its oxide?
Solution
The chemical process used for obtaining a metal from its oxide is reduction. In this process, the metal oxide is reduced to the corresponding metal. The specific reduction method depends on the reactivity of the metal:
- Heating alone: For oxides of less reactive metals (e.g., HgO).
- Reduction with carbon: For oxides of moderately reactive metals (e.g., ZnO, Fe₂O₃).
- Electrolytic reduction: For oxides of highly reactive metals (e.g., Al₂O₃).
Q1QUESTIONS (In-text, Set 4)
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?
Solution
A displacement reaction will occur when a more reactive metal is heated with the oxide of a less reactive metal. The reactivity order of the given metals is: Magnesium > Zinc > Copper.
Based on this, the displacement reactions will take place in the following cases:
| Metal | Zinc Oxide () | Magnesium Oxide () | Copper Oxide () |
|---|---|---|---|
| Zinc (Zn) | No Reaction | No Reaction | Displacement |
| Magnesium (Mg) | Displacement | No Reaction | Displacement |
| Copper (Cu) | No Reaction | No Reaction | No Reaction |
- Zinc Oxide will be displaced by Magnesium.
- Copper Oxide will be displaced by Zinc and Magnesium.
- Magnesium Oxide will not be displaced by either Zinc or Copper as Magnesium is the most reactive.
Q2QUESTIONS (In-text, Set 4)
Which metals do not corrode easily?
Solution
Metals that are least reactive do not corrode easily. These metals are at the bottom of the reactivity series, such as gold (Au), platinum (Pt), and silver (Ag).
Q3QUESTIONS (In-text, Set 4)
What are alloys?
Solution
An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. Alloys are prepared to enhance the properties of the primary metal, such as its hardness, strength, or resistance to corrosion. Examples include brass (an alloy of copper and zinc) and steel (an alloy of iron and carbon).