Metals and Non-metals — Class 10 Science
Science · Chapter 3
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Chapter summary
Key ideas & terms
- Reactivity series
- Metals arranged in order of decreasing reactivity.
- Ionic compound
- A compound formed by transfer of electrons between metal and non-metal.
- Corrosion
- Gradual degradation of a metal by reaction with its surroundings.
- Alloy
- A homogeneous mixture of a metal with other metals or non-metals.
Extra questions & answers
Why is sodium stored under kerosene?
Sodium is so reactive that it catches fire on contact with air or moisture, so kerosene keeps it away from both.
Why are ionic compounds usually solids with high melting points?
Strong electrostatic forces between oppositely charged ions require a lot of energy to break.
List the main physical properties of metals.
Metals are generally lustrous, hard, malleable, ductile, sonorous and good conductors of heat and electricity, with high melting points.
How do metals and non-metals differ chemically?
Metals lose electrons to form positive ions and basic oxides, while non-metals gain electrons to form negative ions and acidic or neutral oxides.
What is the reactivity series, and why is it useful?
A list of metals arranged in order of decreasing reactivity; it predicts displacement reactions and helps decide the method of extracting a metal.
How are ionic compounds formed, and what are their properties?
They form by transfer of electrons from a metal to a non-metal; they are usually solids with high melting points, soluble in water, and conduct electricity when molten or in solution.
What are minerals, ores and gangue?
Minerals are naturally occurring metal compounds; ores are minerals from which a metal can be profitably extracted; gangue is the unwanted earthy impurity in an ore.
How are metals of medium reactivity extracted from their ores?
Their sulphide or carbonate ores are converted to oxides by roasting or calcination, and the oxide is then reduced to the metal, usually with carbon.
Why are some metals like sodium and aluminium extracted by electrolysis?
Because they are very reactive and their oxides cannot be reduced by carbon, so the metals are obtained by electrolytic reduction of their molten compounds.
What is an alloy, and why are alloys made?
An alloy is a homogeneous mixture of a metal with other metals or non-metals; alloying improves properties such as strength, hardness and resistance to corrosion, e.g. steel and brass.
QUESTIONS
1. Give an example of a metal which
(i) is a liquid at room temperature.
Mercury is a metal that is liquid at room temperature.
1. Give an example of a metal which
(ii) can be easily cut with a knife.
Sodium can be easily cut with a knife because it is very soft.
1. Give an example of a metal which
(iii) is the best conductor of heat.
Silver is the best conductor of heat.
1. Give an example of a metal which
(iv) is a poor conductor of heat.
Lead is a comparatively poor conductor of heat.
2. Explain the meanings of malleable and ductile.
A malleable substance can be beaten or rolled into thin sheets. A ductile substance can be drawn into thin wires.
QUESTIONS
1. Why is sodium kept immersed in kerosene oil?
Sodium reacts vigorously with oxygen and moisture in the air and may catch fire. It is therefore kept immersed in kerosene oil, which prevents its contact with air and water.
2. Write equations for the reactions of
(i) iron with steam
Iron reacts with steam to form iron oxide and hydrogen:
2. Write equations for the reactions of
(ii) calcium and potassium with water
Calcium reacts with water as follows:
Potassium reacts with water as follows:
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?
Metal B is the most reactive because it displaces iron from iron(II) sulphate, whereas it does not displace zinc from zinc sulphate.
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.
(ii) What would you observe if B is added to a solution of Copper(II) sulphate?
Metal B would displace copper from copper(II) sulphate solution. A reddish-brown deposit of copper would form on B, and the blue colour of the solution would become lighter or disappear.
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.
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
The order of decreasing reactivity is:
4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute
Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal. Iron reacts with dilute sulphuric acid to form iron(II) sulphate and hydrogen:
5. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Zinc is more reactive than iron, so it displaces iron from iron(II) sulphate solution. Iron is deposited on the zinc, and the pale-green colour of the iron(II) sulphate solution fades. The reaction is:
QUESTIONS
1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
Sodium has one valence electron, oxygen has six valence electrons, and magnesium has two valence electrons. Their electron-dot structures may be represented as
1. (ii) Show the formation of
In the formation of sodium oxide, two sodium atoms each lose one electron and one oxygen atom gains both electrons:
In the formation of magnesium oxide, one magnesium atom loses two electrons and one oxygen atom gains them:
1. (iii) What are the ions present in these compounds?
Sodium oxide contains
2. Why do ionic compounds have high melting points?
Ionic compounds contain oppositely charged ions held together by strong electrostatic forces of attraction. A large amount of heat energy is needed to overcome these forces, so ionic compounds have high melting points.
QUESTIONS
1. Define the following terms.
(i) Mineral
A mineral is an element or compound that occurs naturally in the earth's crust.
1. Define the following terms.
(ii) Ore
An ore is a mineral that contains a sufficiently high percentage of a particular metal so that the metal can be extracted profitably.
1. Define the following terms.
(iii) Gangue
Gangue consists of unwanted impurities, such as soil, sand and rocky materials, that are mixed with an ore.
2. Name two metals which are found in nature in the free state.
Gold and platinum are found in nature in the free state.
3. What chemical process is used for obtaining a metal from its oxide?
Reduction is used for obtaining a metal from its oxide. The oxide may be reduced by heating it with a suitable reducing agent such as carbon, or by another method suited to the metal's reactivity.
QUESTIONS
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?
A displacement reaction occurs when the added metal is more reactive than the metal present in the oxide. Magnesium displaces zinc from zinc oxide:
Zinc displaces copper from copper oxide:
Magnesium also displaces copper from copper oxide:
No other displacement reaction occurs among the combinations shown.
2. Which metals do not corrode easily?
Metals that are low in the reactivity series, such as gold, platinum and silver, do not corrode easily.
3. What are alloys?
Alloys are homogeneous mixtures of two or more metals, or of a metal and a non-metal, prepared in definite proportions to obtain desired properties.
EXERCISES
1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b)
(c)
(d)
(d)
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.
(c) Applying a coating of zinc. Grease may contaminate food and paint can burn or peel on heating, whereas zinc coating protects the iron from rusting.
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.
(a) Calcium. Calcium forms the ionic oxide
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.
(c) Zinc is more reactive than tin. If the coating is damaged, zinc may react with acids present in food, whereas tin is less reactive and is safer for coating food cans.
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?
First, strike or hammer each sample. A metal will generally flatten into a sheet because it is malleable, whereas a solid non-metal will generally break because it is brittle. Next, connect each sample in an electric circuit containing the battery, bulb and switch. The bulb will usually glow with a metal because metals conduct electricity, but it will usually not glow with a non-metal.
5. You are given a hammer, a battery, a bulb, wires and a switch.
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
The tests are useful for making a general distinction, but they are not completely reliable because there are exceptions. Graphite is a non-metal that conducts electricity, while some metals are soft or brittle and may not behave as expected in the hammer test.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Amphoteric oxides are oxides that react with both acids and bases to form salt and water. Aluminium oxide,
7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Zinc and iron will displace hydrogen from dilute acids because they are above hydrogen in the reactivity series. Copper and silver will not displace hydrogen because they are below hydrogen in the series.
8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
The impure metal M is used as the anode, a thin strip of pure metal M is used as the cathode, and a solution of a soluble salt of metal M is used as the 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?
The gas will have no effect on dry litmus paper because an acidic substance shows its acidic character only in the presence of water.
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
(ii) moist litmus paper?
The gas will turn moist blue litmus paper red. Sulphur dioxide dissolves in water on the moist paper and forms sulphurous acid.
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.
(b) Write a balanced chemical equation for the reaction taking place.
Sulphur burns in oxygen to form sulphur dioxide:
The sulphur dioxide then dissolves in water to form sulphurous acid:
10. State two ways to prevent the rusting of iron.
Rusting of iron can be prevented by painting its surface and by galvanising it with a protective coating of zinc.
11. What type of oxides are formed when non-metals combine with oxygen?
Non-metals generally form acidic oxides when they combine with oxygen. Some non-metal oxides, such as carbon monoxide, are neutral.
12. Give reasons
(a) Platinum, gold and silver are used to make jewellery.
Platinum, gold and silver are lustrous, malleable and ductile, so they can be shaped into attractive ornaments. They are also very unreactive and therefore do not corrode easily.
12. Give reasons
(b) Sodium, potassium and lithium are stored under oil.
Sodium, potassium and lithium are highly reactive metals. They react rapidly with oxygen and moisture in the air and may catch fire, so they are stored under oil to prevent contact with air and water.
12. Give reasons
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
Aluminium quickly forms a thin, tough and protective layer of aluminium oxide on its surface. This layer prevents further reaction and corrosion. Aluminium also conducts heat well and has a high melting point, making it suitable for cooking utensils.
12. Give reasons
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Metal oxides are generally easier to reduce to metals than the corresponding carbonates or sulphides. Carbonate ores are therefore converted into oxides by calcination, while sulphide ores are converted into oxides by roasting.
13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Tarnished copper vessels have a green coating of basic copper carbonate. Lemon and tamarind contain acids that react with this basic coating and dissolve it, exposing the clean copper surface underneath.
14. Differentiate between metal and non-metal on the basis of their chemical properties.
Metals generally lose electrons and form positively charged ions, whereas non-metals generally gain electrons and form negatively charged ions. Metals usually form basic oxides, although some form amphoteric oxides, while non-metals usually form acidic or neutral oxides. Metals above hydrogen in the reactivity series react with dilute acids to release hydrogen gas, whereas non-metals do not displace hydrogen from dilute acids. A more reactive metal can displace a less reactive metal from its salt solution, while non-metals generally do not show such displacement.
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?
He most likely used aqua regia, a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio
16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Copper is a good conductor of heat and does not react with hot water or steam. Iron present in steel can react with steam and is also more likely to corrode in the presence of water and air. Copper is therefore more suitable for making hot water tanks.