Nature of Matter: Elements, Compounds, and Mixtures Class 8 Extra Questions and Answers Science Chapter 8

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Class 8 Science Chapter 8 Nature of Matter: Elements, Compounds, and Mixtures Extra Questions

Class 8 Science Chapter 8 Extra Questions on Nature of Matter: Elements, Compounds, and Mixtures

Nature of Matter: Elements, Compounds, and Mixtures Class 8 Very Short Question Answer

Question 1.
What is the simplest form of matter?
Answer:
Element

Question 2.
What is formed by the chemical combination of elements?
Answer:
Compound

Question 3.
What is formed by the physical combination of elements?
Answer:
Mixture

Question 4.
What is the building block of matter?
Answer:
Atom

Question 5.
What type of change does not form a new substance?
Answer:
Physical Change

Question 6.
What kind of mixture is air?
Answer:
Uniform Mixture

Question 7.
What do you mean by matter?
Answer:
Anything that has mass and occupies space is called matter.

Nature of Matter: Elements, Compounds, and Mixtures Class 8 Short Question Answer

Question 1.
What are metals and non-metals?
Answer:
Metals are elements that are shiny, good conductors of heat and electricity. Whereas non-metals are dull in appearance and poor conductors of heat and electricity.

Question 2.
What is the main difference between physical and chemical change?
Answer:
When physical change happens, no new substance forms, whereas in a chemical change, it happens.

Question 3.
What do you mean by metalloids?
Answer:
Metalloids are elements that have properties of both metals and non-metals. They are known as semimetals.

Question 4.
Define mixture.
Answer:
Mixtures can be defined as a kind of matter that is formed by mixing two or more pure substances (elements and compounds) in any proportion, such that they do not undergo any chemical change and retain their individual properties.

Question 5.
Why is it necessary to separate the constituents of a mixture?
Answer:
It is necessary to separate the constituents of a mixture because:

• To remove unwanted and harmful substances.
• To obtain pure and useful substances.

Question 6.
Why are metals considered elements?
Answer:
Metals are considered elements because they consist of only one type of atom.
For example, Copper (Cu), Iron (Fe), and Gold (Au) are pure substances.

Question 7.
How do metals form compounds?
Answer:
Metals form compounds by donating electrons to non-metals during chemical reactions. This results in ionic bonding, creating substances like metal oxides and metal chlorides.

Question 8.
What is a mineral, and how is it different from rock?
Answer:
A mineral is a naturally occurring, inorganic substance with a definite chemical composition and a crystalline structure. In contrast, a rock is a solid material made up of one or more minerals.

Question 9.
What are pure substances?
Answer:
A pure substance is a type of matter that has a uniform and definite composition. It contains only one kind of particle, either a single element (like oxygen or gold) or a single compound (water or salt), and cannot be separated into other substances by physical means.

Question 10.
Differentiate between elements and compounds.
Answer:

Elements	Compounds
1. Elements are a single type of atom.	1. Compounds are made up of two or more elements.
2. Elements consist of only one kind of atom.	2. Compounds consist of two or more different elements chemically combined.
3. Elements cannot be broken down into sub-parts.	3. Compounds can be broken down into sub-parts.
4. Properties depend on the atom type Examples: Hydrogen (H), Iron (Fe) & Sulfur (S), etc.	4. Properties are different from the elements it’s made of. Examples: Water (H2O), Methane (CH4), & Salt (NaCl), etc.

Question 11.
Define:
(a) Elements
(b) Compounds
Answer:
(a) An element is a pure substance that cannot be converted into anything simpler than itself by any physical or chemical process. It is made up of only one kind of atom.
(b) A compound is a pure substance composed of two or more elements combined chemically in a definite proportion by mass.

Question 12.
Give two examples for each of the following:
(a) Metals
(b) Non-metals
(c) Metalloids
(d) Inert gases
Answer:
(a) Metals – Gold and Silver
(b) Non-metals – Oxygen and Sulphur
(c) Metalloids – Boron and Silicon
(d) Inert gases – Helium and Neon

Question 13.
Classify the following substances into compounds and mixtures:
Carbon dioxide, air, water, milk, common salt, blood, fruit juice, and iron sulphide.
Answer:
Compounds: Carbon dioxide, Iron sulphide, Water, Common Salt.
Mixtures: Air, Milk, Fruit Juice.

Nature of Matter: Elements, Compounds, and Mixtures Class 8 Long Question Answer

Question 1.
Differentiate between pure and impure substances.
Answer:

Pure Substances	Impure Substances
Pure substances have a definite chemical composition and definite physical and chemical properties.	Impure substances are made up of two or more pure substances mixed in any proportion. They do not have a definite set of properties.
Pure substances are all uniform, i.e., their composition is uniform throughout the bulk.	Impure substances may be non-uniform or uniform i.e., their composition is not uniform throughout the bulk.
Examples are gold, silver, water, sodium chloride, etc.	Examples are air, seawater, a solution of sugar in water, etc.

Question 2.
State four differences between compounds and mixtures.
Answer:

Compounds	Mixtures
A compound is a pure substance.	A mixture is an impure substance.
Compounds are always homogeneous.	Mixtures may be uniform or non-uniform.
Formation of a compound involves a change in energy.	Formation of a mixture does not involve any change in energy.
Components of compounds can be separated only by complex chemical processes.	Components of mixtures can be separated by simple physical methods of separation.

Question 3.
Differentiate between elements, compounds, and mixtures, highlighting their key characteristics and providing examples for each.
Answer:
(i) Elements

• Definition: A pure substance consisting of only one type of atom is called an atom.
• Composition: It is made up of identical atoms, each with the same number of protons.
• Properties: Elements possess unique and distinct physical and chemical properties.
• Separation: It cannot be broken down into simpler substances by ordinary chemical or physical means.
• Examples: Gold (Au), Oxygen (O), Iron (Fe), Sodium (Na).

(ii) Compounds

• Definition: A pure substance formed when two or more different elements chemically combine in a fixed proportion by mass.
• Composition: It consists of molecules where different types of atoms are chemically bonded together in a specific ratio.
• Properties: Compounds exhibit entirely new properties different from their constituent elements.
  For example, water (H₂O) is a liquid at room temperature, while its constituent elements, hydrogen and oxygen, are gases.
• Separation: It can only be broken down into its constituent elements through chemical or electrochemical reactions.
• Examples: Water (H₂O)

(iii) Mixtures

• Definition: A combination of two or more substances (elements or compounds) that are physically blended but not chemically bonded.
• Composition: The components can be present in any proportion, and the composition can be variable.
• Properties: Each component retains its individual physical and chemical properties within the mixture.
  For example, in a mixture of iron filings and sulfur powder, both retain their respective magnetic and yellow color properties.
• Separation: It can be separated into its constituent substances using physical methods based on differences in their physical properties (e.g., filtration, evaporation, magnetism).
• Types: It can be either homogeneous (uniform composition throughout, like saltwater or air) or heterogeneous (non-uniform composition with visibly distinct parts, like sand and water or a salad).
• Examples: Air, saltwater, soil, sugar solution.

Question 4.
Discuss the importance and applications of elements, compounds, and mixtures in our daily lives.
Answer:
Elements, compounds, and mixtures are the basic building blocks of all matter. They play key roles in daily life and various industries.

Elements
Importance: Elements are the simplest form of matter and cannot be further broken down, making them the foundation of all other substances.
Applications:

• Metals like iron, copper, and aluminum are used in construction, wiring, and packaging due to their strength, conductivity, and malleability.
• Non-metals like oxygen are essential for respiration and combustion.
• Silicon is vital for electronics and computer technology.
• Gold and silver are valued for jewelry and in some electronic components.

Compounds
Importance: Compounds are formed by the chemical combination of elements, resulting in substances with unique properties necessary for life and various technological advancements.
Applications:

• Water (H₂O) is indispensable for life, used for drinking, cooking, and industrial processes.
• Table salt (NaCl) is a fundamental seasoning and food preservative.
• Sugar (C₁₂H₂₂O₁₁) is a crucial energy source.
• Many medicines and pharmaceuticals are pure compounds designed to interact with the body in specific ways.
• Carbon dioxide (CO₂) is involved in respiration and photosynthesis.

Mixtures
Importance: Most of the matter encountered daily exists as mixtures. Understanding mixtures is essential for various applications.
Applications:

• Air, a mixture of gases like nitrogen and oxygen, is vital for breathing and weather phenomena.
• Alloys, like steel and bronze, are mixtures of metals that possess enhanced properties like strength or corrosion resistance, used in construction and various manufactured goods.
• Food products like milk, juice, and granola are mixtures, combining different components for taste, nutrition, or texture.
• Soil is a complex mixture of minerals, organic matter, and living organisms, crucial for plant growth.
• Many everyday products like paints, cleaning solutions, and cosmetics are mixtures designed for specific purposes.

Question 5.
Why are compounds considered pure substances, while mixtures are not?
Answer:
Compounds are pure substances because they are made up of only one type of molecule and have a uniform and definite composition throughout. For example, every molecule of water (H₂O) is identical, consisting of two hydrogen atoms and one oxygen atom chemically bonded together. This fixed composition results in consistent physical and chemical properties, like a specific boiling point and density.

Mixtures are not pure substances because they consist of two or more substances that are physically blended, not chemically bonded. The components of a mixture retain their individual properties and can be present in varying proportions. For example, air is a mixture of nitrogen, oxygen, and other gases, and the amount of each gas can vary.

Nature of Matter: Elements, Compounds, and Mixtures Extra Questions for Practice

Question 1.
What is an element?

Question 2.
What is a compound?

Question 3.
What is a mixture?

Question 4.
Is water a compound or a mixture?

Question 5.
Can an element be broken down?

Question 6.
Is air a pure substance?

Question 7.
Can a compound be separated into its elements?

Question 8.
How do mixtures differ from compounds?

Question 9.
Why is oxygen considered an element?

Question 10.
What makes a substance ‘pure’?

Question 11.
Why is salt water a mixture?

Question 12.
How is a uniform mixture different from a non-uniform one?

Question 13.
Explain how elements and compounds differ in composition and properties.

Question 14.
Describe the process and criteria used to separate mixtures into their components.

Question 15.
How does the molecular structure of a compound affect its physical and chemical properties?

Question 16.
Compare the methods of identifying pure substances versus mixtures in a laboratory.

Question 17.
How does the classification of matter help in understanding chemical reactions?