Last updated on February 6th, 2024 at 12:47 am
Chhattisgarh Board Class 8 Science Chapter 5 Solution Textbook question and answers as well as extra question and answers from the chapter
Choose the correct alternative :-
This is not a property of metals
a) Fragility b) Conduction of electricity
c) High density d) Malleability and ductility
Correct Answer: a) Fragility
Out of the three pins of gold, silver and iron which pin can get a coat of copper when dipped in copper sulphate solution :-
a) Iron b) Gold c) Silver d) None of these
Correct Answer: c) Silver
Which halogen is used as an antiseptic?
a) Fulorine b) Chlorine c) Bromine d) Iodine
Correct Answer: d) Iodine
Iron rusts :-
a) Only in air b) Only in presence of carbon dioxide
c) Only in water d) In presence of both air and water
Correct Answer: d) In presence of both air and water
An example of Noble metal is :-
a) Iron b) Copper c) Gold d) Aluminium
Correct Answer: c) Gold
Which of these is classified as metal or non-metal :-
a) Element b) Compound c) Mixture d) All of these
Correct Answer: a) Element
Fill in the blanks
- Noble metals are usually unreactive.
- Breaking up of the non-metals into pieces is known as brittleness.
- On burning, metals form oxides.
- The main constituent of German silver is nickel.
- Steel alloy is used in the manufacture of rails.
Match the following :-
- Duralumin – Parts of aeroplane
- Stainless Steel – Medical Instrument used in surgery
- Phosphorous – Match box
- Chlorine – Disinfectant
- Gold – Ornaments
Mark the statements true or false :-
- All metals are solid at room temperature.[T]
- Sodium is more reactive than magnesium.[F]
- Stainless steel is an alloy of iron, nickel, carbon and chromium.[F]
- Non metals react with oxygen to form alkaline oxides (basic oxide).[F]
- Rusting is an example of corrosion of metals.[T]
Answer the following questions :-
Differenciate metals and non metals on the basis of physical and chemical properties. Write three differences of each.
Metals
| Metals are typically shiny and have metallic luster.
Metals are generally good conductors of heat and electricity. Metals are malleable and ductile, meaning they can be hammered into thin sheets and drawn into wires.
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Metals tend to lose electrons to form positive ions (cations) in chemical reactions.
Most metals react with oxygen to form metal oxides, which are basic in nature. Metals generally react with acids to form salts and hydrogen gas.
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| Non Metals Physical | |
| Non-metals are usually dull and lack metallic luster.
Non-metals are poor conductors of heat and electricity. Non-metals are brittle and cannot be easily hammered into thin sheets or drawn into wires.
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Non-metals tend to gain electrons to form negative ions (anions) in chemical reactions.
Non-metals react with oxygen to form non-metal oxides, which are acidic or neutral in nature. Non-metals may react with acids, but the products are not always salts and hydrogen gas.
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Why is gold and silver used for making ornaments?
Gold and silver are used for making ornaments because they are noble metals, which means they are resistant to corrosion and do not react easily with environmental factors like air and moisture. Additionally, they have a high luster, are malleable, and can be easily shaped into intricate designs.
What do you understand by reactivity series?
The reactivity series is a list of metals arranged in order of their decreasing chemical activity. The series helps predict the likelihood of a metal reacting with other substances. Metals higher in the reactivity series tend to lose electrons more readily and are more likely to react with acids or other compounds.
How much carat is pure gold? Why is pure gold not used for making ornaments?
Pure gold is 24 carats. Pure gold is not used for making ornaments because it is too soft and malleable. The addition of other metals, such as copper or silver, in varying proportions forms alloys like 18-carat gold, which are more durable and suitable for jewelry.
What are alloys? Give names of any four alloys and write their constituents and uses.
Alloys are mixtures of two or more elements, with at least one being a metal. Four examples are:
- Brass: Copper (Cu) and Zinc (Zn), used in making musical instruments.
- Bronze: Copper (Cu) and Tin (Sn), used in making sculptures and medals.
- Stainless Steel: Iron (Fe), Chromium (Cr), Nickel (Ni), used in kitchenware and construction.
- Duralumin: Aluminum (Al), Copper (Cu), used in aircraft construction.
What is metal corrosion? What are the ways to protect corrosion?
Metal corrosion is the gradual deterioration of metal due to its reaction with environmental factors, such as oxygen and moisture. Ways to protect against corrosion include:
- Applying a protective coating (painting).
- Applying grease or oil to create a barrier.
- Using metallic coatings (galvanization).
- Making alloys that resist corrosion.
Why is graphite used as an electrode?
Graphite is used as an electrode because it is a good conductor of electricity and has high thermal stability. It can withstand the high temperatures and intense conditions in various electrical applications, such as batteries and electrolysis cells.
