Nature of Matter: Elements, Compounds Class 8 - Chapter 8 Curiosity

Q 1
Question
Consider the following reaction where two substances, A and B, combine to form a product C: A + B → C. Assume that A and B cannot be broken down into simpler substances by chemical reactions. Based on this information, which of the following statements is correct?
(i) A, B, and C are all compounds and only C has a fixed composition.
(ii) C is a compound, and A and B have a fixed composition.
(iii) A and B are compounds, and C has a fixed composition.
(iv) A and B are elements, C is a compound, and has a fixed composition.
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Q 2
Question
Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.
(i) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.
(iii) Assertion is true, but Reason is false.
(iv) Assertion is false, but Reason is true.
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Q 3
Question
Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.
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Q 4
Question
In which of the following cases are all the examples correctly matched? Give reasons in support of your answers.
(i) Elements — water, nitrogen, iron, air.
(ii) Uniform mixtures — minerals, seawater, bronze, air.
(iii) Pure substances — carbon dioxide, iron, oxygen, sugar.
(iv) Non-uniform mixtures — air, sand, brass, muddy water.
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Q 5
Question
Iron reacts with moist air to form iron oxide, and magnesium burns in oxygen to form magnesium oxide. Classify all the substances involved in the above reactions as elements, compounds or mixtures, with justification.
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Q 6
Question
Classify the following as elements, compounds, or mixtures in Table 8.3: Carbon dioxide, sand, seawater, magnesium oxide, muddy water, aluminium, gold, oxygen, rust, iron sulfide, glucose, air, water, fruit juice, nitrogen, sodium chloride, sulfur, hydrogen, baking soda. Identify pure substances amongst these and list them below.
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Q 7
Question
What new substance is formed when a mixture of iron filings and sulfur powder is heated, and how is it different from the original mixture? Also, write the word equation for the reaction.
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Q 8
Question
Is it possible for a substance to be classified as both an element and a compound? Explain why or why not.
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Q 9
Question
How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?
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Q 10
Question
Analyse Fig. 8.24. Identify Gas A. Also, write the word equation of the chemical reaction. (Iron filings are placed in a test tube with dilute hydrochloric acid, and a gas labelled Gas A is collected.)
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Q 11
Question
Write the names of any two compounds made only from non-metals, and also mention two uses of each of them.
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Q 12
Question
How can gold be classified as both a mineral and a metal?
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Project 1
Project
Design and create comic strips from real-life examples to differentiate between elements, compounds, and mixtures with diagrams and illustrate their properties and uses.
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Key Points
Use simple characters and everyday examples to show each type.
Key Points / Good Practices
Show an element as a single character (e.g. gold, oxygen).
Show a compound as two characters tightly joined (e.g. water = H + O).
Show a mixture as characters standing together but separable (e.g. salad).
Add speech bubbles giving each one's property and use.
Use real-life scenes — a kitchen, a bridge, the air outside.
Keep panels colourful and label each substance clearly.
A good comic makes the three categories instantly clear through relatable characters and scenes.

Project 2
Project
Search for discoveries of some elements (such as phosphorus, sodium), compounds (such as penicillin) and mixtures (such as brass, bronze, stainless steel). Present your findings in the class.
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Key Points
Group findings as elements, compounds, and mixtures.
Key Points / Good Practices
Elements: note who discovered phosphorus and sodium, and when.
Compounds: explain how penicillin was discovered and its use as a medicine.
Mixtures: describe how alloys like brass and bronze were made.
Mention how stainless steel improved everyday tools.
Use a timeline to show the order of discoveries.
Cite reliable books or trusted websites for your facts.
A clear timeline and grouping by category makes the discovery stories easy to follow.

Project 3
Project
Let us search: Read labels on items like detergents or snacks, and try to list the mixtures and compounds they contain.
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Key Points
Sort each listed ingredient as a compound or a mixture.
Key Points / Good Practices
Pick a detergent and a snack with a clear ingredient list.
Make two columns: compounds and mixtures.
Sodium chloride and baking soda are compounds.
The whole detergent or snack is itself a mixture.
Note any ingredient you are unsure of for class discussion.
Compare lists with classmates to find common substances.
Everyday labels show that products are mixtures built from many compounds.

Project 4
Project
Work in groups: Each group will pretend to be in the role of either an element, a compound, or a mixture. Debate which category among them is the most important.
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Key Points
Each category is important in its own way.
Key Points / Good Practices
Elements team: argue they are the building blocks of everything.
Compounds team: argue they make water, medicines, and food.
Mixtures team: argue air, alloys, and food are all mixtures.
Each group gives real examples to support its case.
Listen respectfully and respond with facts, not just opinion.
Conclude that all three are needed for life and technology.
A fair debate shows that elements, compounds, and mixtures each matter and depend on one another.