Complete Solutions and Summary of Nature of Matter: Elements, Compounds, and Mixtures – Curiosity Class 8, Science, Chapter 8 – Summary, Questions, Answers, Extra Questions

Detailed summary and explanation of Chapter 8 ‘Nature of Matter: Elements, Compounds, and Mixtures’ with all question answers, extra questions, and solutions from Curiosity Class VIII, Science.

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Nature of Matter: Elements, Compounds, and Mixtures - Complete Study Guide

Chapter Overview

118 Known Elements

78% Nitrogen in Air

2:1 H:O Ratio in Water

1:1 Na:Cl Ratio in Salt

What You'll Learn

Mixtures

Understanding mixtures, their types (uniform and non-uniform), and examples like air, poha, and sprout salad.

Pure Substances

Exploring elements and compounds, their properties, and differences from mixtures.

Elements

Learning about atoms, molecules, metals, non-metals, and metalloids as building blocks of matter.

Compounds

Studying how elements combine in fixed ratios to form compounds with new properties.

Historical Context

This chapter explores the nature of matter through ancient Indian heritage like 'Mishraloha' (alloys) mentioned in texts such as Charaka Samhita and Susruta Samhita, used for medicinal purposes. It discusses modern concepts like alloys (e.g., bronze, stainless steel) and innovations in materials like graphene aerogel for environmental cleanup.

Key Highlights

Matter consists of elements, compounds, and mixtures. Activities demonstrate air as a mixture, water as a compound via electrolysis, and differences between mixtures and compounds using iron and sulfur. Minerals are natural compounds or elements, essential for everyday items like cement and talcum powder.

Comprehensive Chapter Summary

1. Introduction to Matter

The chapter begins with examples of matter around us, like staircases, air, water, food, clothes, books, trees, and sticks. Matter is made of tiny particles, and most things are mixtures of substances. It poses questions on entities consisting of matter, combining elements into compounds, and environmental applications of compounds.

2. What Are Mixtures?

Definition and Examples

A mixture is formed when two or more substances mix without chemical reaction, retaining properties. Examples: poha, sprout salad (non-uniform), sugar in water (uniform).

Uniform vs Non-Uniform

Non-uniform: Components visible (e.g., sprout salad). Uniform: Evenly distributed, not distinguishable (e.g., sugar-water, alloys like stainless steel, brass, bronze).

Ancient Indian Alloys

Mishraloha: Mixtures of metals like bronze (copper + tin) for digestion and immunity.

3. Is Air a Mixture?

Composition and Activity

Air is a uniform mixture of nitrogen (78%), oxygen, argon, CO2, water vapor. Activity 8.1 shows CO2 presence via lime water turning milky.

Dust in Air

Activity 8.2 demonstrates suspended dust particles as pollutants, varying by location. Major pollutants: dust, soot, CO, ozone, NO2, SO2. AQI measures air quality.

4. Types of Mixtures

Classification

Gas-gas (air: uniform), gas-liquid (aerated water: uniform), solid-gas (carbon in air: non-uniform), liquid-liquid (vinegar: uniform; oil-water: non-uniform), solid-liquid (seawater: uniform; sand-water: non-uniform), solid-solid (alloys: uniform; baking powder: uniform).

5. Pure Substances

Definition

Pure substance: Cannot be separated by physical processes; same type of particles. Common usage 'pure' means unadulterated, but scientifically, it means single substance (e.g., milk is mixture, baking soda is pure).

Types

Elements (cannot break down) and compounds (elements combined in fixed ratios with new properties).

6. Elements

Activity 8.3: Electrolysis breaks water into H2 and O2 (elements). 118 known elements; most solids, 11 gases, 2 liquids. Atoms form molecules (e.g., H2, O2). Classified as metals (gold, iron), non-metals (carbon, sulfur), metalloids (silicon).

7. Compounds

Activity 8.4: Heating sugar yields carbon and water, showing it's a compound (C, H, O). Activity 8.5: Iron + sulfur forms iron sulfide with new properties. Compounds have fixed ratios, different properties from elements (e.g., water extinguishes fire unlike H2 and O2).

8. Uses of Elements, Compounds, and Mixtures

Air (mixture), water (compound), metals for construction. Innovations: Medicines, fertilizers, alloys like stainless steel, graphene aerogel for cleanup. Indian art: Dhokra uses brass/bronze mixtures.

9. What Are Minerals?

Minerals: Natural solids with fixed composition; native (pure elements like gold) or compounds (quartz, calcite). Used in cement, talcum powder. Not everything is matter (light, heat, thoughts).

10. Snapshots

Mixtures: Components retain properties. Pure substances: Elements or compounds. Minerals: Mostly compounds.

Questions and Answers from Chapter

Short Questions

Q1. Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

Answer: (i) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

Q2. Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.

Answer: Hydrogen is a fuel, oxygen supports combustion, but water extinguishes fire.

Q3. In which of the following cases are all the examples correctly matched?

Answer: (iii) Pure substances— carbon dioxide, iron, oxygen, sugar.

Q4. Iron reacts with moist air to form iron oxide, and magnesium burns in oxygen to form magnesium oxide. Classify all the substances involved.

Answer: Iron, magnesium, oxygen: elements; iron oxide, magnesium oxide: compounds; moist air: mixture.

Q5. Classify the following as elements, compounds, or mixtures: Carbon dioxide, sand, seawater.

Answer: Carbon dioxide: compound; sand: mixture; seawater: mixture.

Q6. What new substance is formed when a mixture of iron filings and sulfur powder is heated?

Answer: Iron sulfide.

Q7. Is it possible for a substance to be classified as both an element and a compound?

Answer: No.

Q8. How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?

Answer: It would be explosive and not support life as we know it.

Q9. Analyze Fig. 8.24. Identify Gas A.

Answer: Hydrogen.

Q10. Write the names of any two compounds made only from non-metals.

Answer: Water, carbon dioxide.

Q11. How can gold be classified as both a mineral and a metal?

Answer: Gold is a native mineral (pure element) and a metal.

Q12. What is a mixture?

Answer: Two or more substances mixed without chemical reaction.

Q13. What is air's composition?

Answer: Nitrogen 78%, oxygen, argon, CO2, water vapor.

Q14. What are alloys?

Answer: Uniform mixtures of metals.

Q15. What are elements?

Answer: Simplest substances made of identical atoms.

Medium Questions

Q1. 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?

Answer: (iv) A and B are elements, C is a compound, and has a fixed composition. A and B are elements as they cannot be broken down, and C is a compound formed by their combination in a fixed ratio. (3 marks)

Q2. Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

Answer: (i) Both Assertion and Reason are true and Reason is the correct explanation for Assertion. Air consists of gases like nitrogen and oxygen mixed without reaction, fitting the definition of a mixture. (3 marks)

Q3. Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.

Answer: Hydrogen is a fuel, oxygen supports combustion, but water extinguishes fire. This shows compounds have properties different from their elements due to chemical bonding. (3 marks)

Q4. In which of the following cases are all the examples correctly matched? Give reasons in support of your answers.

Answer: (iii) Pure substances— carbon dioxide, iron, oxygen, sugar. These are either elements (iron, oxygen) or compounds (CO2, sugar), unlike others which mix categories. (3 marks)

Q5. 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.

Answer: Iron, magnesium, oxygen: elements (cannot break down). Iron oxide, magnesium oxide: compounds (fixed ratios). Moist air: mixture (gases and water vapor). (3 marks)

Q6. 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.

Q7. 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.

Answer: Iron sulfide; it has uniform properties, not separable by magnet, unlike the mixture. Iron + Sulfur → Iron sulfide. (3 marks)

Q8. Is it possible for a substance to be classified as both an element and a compound? Explain why or why not.

Answer: No; elements cannot be broken down, compounds are combinations of elements in fixed ratios with different properties. (3 marks)

Q9. How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?

Answer: It would be flammable and explosive, unfit for drinking or life support, altering biology and safety. (3 marks)

Q10. Analyze Fig. 8.24. Identify Gas A. Also, write the word equation of the chemical reaction.

Answer: Hydrogen; Iron + Dilute Hydrochloric acid → Iron chloride + Hydrogen gas. (3 marks)

Q11. Write the names of any two compounds made only from non-metals, and also mention two uses of each of them.

Answer: Water: Drinking, cleaning. Carbon dioxide: Photosynthesis, fire extinguishers. (3 marks)

Q12. How can gold be classified as both a mineral and a metal?

Answer: Gold is a native mineral (pure element) and exhibits metallic properties like conductivity. (3 marks)

Q13. What is air a mixture?

Answer: Air has gases like nitrogen, oxygen mixed without reaction, shown by lime water test for CO2. (3 marks)

Q14. What are types of mixtures?

Answer: Gas-gas (air), gas-liquid (soda), solid-gas (smoke), etc.; uniform or non-uniform. (3 marks)

Q15. What are pure substances?

Answer: Single type of particles; elements (e.g., iron) or compounds (e.g., water). (3 marks)

Long Questions

Q1. 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?

Answer: (iv) A and B are elements, C is a compound, and has a fixed composition. Elements are substances that cannot be broken down further, like hydrogen and oxygen. When they combine in a fixed ratio, they form a compound like water, which has properties different from A and B. This is demonstrated in Activity 8.3 where water decomposes into hydrogen and oxygen via electrolysis, confirming water as a compound of two elements.

Q2. Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

Answer: (i) Both Assertion and Reason are true and Reason is the correct explanation for Assertion. Air is composed of nitrogen (78%), oxygen, argon, carbon dioxide, and water vapor mixed without chemical reaction, as shown in Activity 8.1 where lime water turns milky due to CO2, and Activity 8.2 showing dust particles suspended. This fits the definition of a mixture where components retain properties and can be separated physically.

Q3. Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.

Answer: Hydrogen is a combustible gas that burns with a pop sound, and oxygen supports combustion, making flames brighter. However, water, formed from H2 and O2 in a 2:1 ratio, extinguishes fire and is a liquid essential for life. This difference arises because compounds have new properties due to chemical bonding, as seen in electrolysis (Activity 8.3) where water breaks into gases, but the compound's behavior is unique.

Q4. In which of the following cases are all the examples correctly matched? Give reasons in support of your answers.

Answer: (iii) Pure substances— carbon dioxide, iron, oxygen, sugar. Carbon dioxide and sugar are compounds (fixed ratios of elements), iron and oxygen are elements (cannot break down). Other options mix categories: (i) includes mixtures like air; (ii) minerals are pure but air is mixture; (iv) air and muddy water are mixtures, brass is alloy (mixture).

Q5. 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.

Answer: Iron and magnesium: elements (pure, cannot break down). Oxygen: element (gas in air). Moist air: mixture (air gases + water vapor). Iron oxide and magnesium oxide: compounds (elements combined in fixed ratios with new properties, like rust formation). Justification from chapter: Elements are building blocks; compounds form via reactions; mixtures retain properties.

Q6. 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.

Answer: Elements: Aluminium, gold, oxygen, nitrogen, sulfur, hydrogen. Compounds: Carbon dioxide, magnesium oxide, rust, iron sulfide, glucose, water, sodium chloride, baking soda. Mixtures: Sand, seawater, muddy water, air, fruit juice. Pure substances among these: Elements and compounds listed above, as they cannot be separated physically into different matter.

Q7. 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.

Answer: Iron sulfide is formed. The original mixture (Sample A) is non-uniform, separable by magnet, and reacts to produce hydrogen gas with HCl. Iron sulfide (Sample B) is uniform black mass, not magnetic, and produces hydrogen sulfide (rotten egg smell) with HCl. Word equation: Iron + Sulfur → Iron sulfide. This shows compound formation with new properties.

Q8. Is it possible for a substance to be classified as both an element and a compound? Explain why or why not.

Answer: No, because elements are simplest substances that cannot be broken down (e.g., hydrogen), while compounds are combinations of elements in fixed ratios with different properties (e.g., water). A substance cannot be both as elements are single types of atoms, compounds multiple. Examples: Gold is element, not compound; water is compound, not element.

Q9. How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?

Answer: Water as a mixture would be unstable, potentially separating into explosive gases, making it unsafe for drinking, cooking, or life. Oceans might ignite, biology (e.g., blood, cells) would fail, and fire-fighting impossible. As a compound, it's stable with unique properties; as mixture, daily activities like hydration or agriculture would be hazardous.

Q10. Analyze Fig. 8.24. Identify Gas A. Also, write the word equation of the chemical reaction.

Answer: Gas A is hydrogen (burns with pop sound). Word equation: Iron + Dilute Hydrochloric acid → Iron chloride + Hydrogen gas. This is from iron reacting in the mixture, as sulfur does not react, showing mixture properties where components react separately.

Q11. Write the names of any two compounds made only from non-metals, and also mention two uses of each of them.

Answer: Water (H, O): Used for drinking (hydration) and cleaning (sanitation). Carbon dioxide (C, O): Used in photosynthesis (plant growth) and fire extinguishers (suppressing fire). Both are non-metal compounds with essential roles in life and safety.

Q12. How can gold be classified as both a mineral and a metal?

Answer: Gold is a native mineral, occurring as a pure element in nature with fixed composition. As a metal, it has properties like malleability, conductivity. Unlike most minerals (compounds like quartz), native minerals are elements, allowing dual classification.

Q13. Explain why air is considered a mixture and describe an activity to prove the presence of carbon dioxide in air.

Answer: Air is a mixture as gases like nitrogen, oxygen mix without reaction, retaining properties. Activity 8.1: Mix calcium oxide with water to form lime water, leave exposed; it turns milky due to calcium carbonate from CO2 reaction, proving CO2 presence.

Q14. Describe the types of mixtures with examples and explain how they differ from pure substances.

Answer: Types: Gas-gas (air: uniform), gas-liquid (soda: uniform), solid-gas (smoke: non-uniform), etc. Mixtures have variable composition, separable physically, components retain properties. Pure substances (elements/compounds) have fixed composition, inseparable physically, uniform particles.

Q15. What are pure substances? Classify milk, packed fruit juice, baking soda, sugar, and soil as mixtures or pure substances according to science.

Answer: Pure substances: Same particles, inseparable physically. Milk: mixture (fats, proteins, water). Fruit juice: mixture (sugars, water, pulp). Baking soda: pure (compound). Sugar: pure (compound). Soil: mixture (minerals, organics).

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Complete Solutions and Summary of Nature of Matter: Elements, Compounds, and Mixtures – Curiosity Class 8, Science, Chapter 8 – Summary, Questions, Answers, Extra Questions

Detailed summary and explanation of Chapter 8 ‘Nature of Matter: Elements, Compounds, and Mixtures’ with all question answers, extra questions, and solutions from Curiosity Class VIII, Science.

Nature of Matter: Elements, Compounds, and Mixtures

Chapter Overview

What You'll Learn

Mixtures

Pure Substances

Elements

Compounds

Historical Context

Key Highlights

Comprehensive Chapter Summary

1. Introduction to Matter

2. What Are Mixtures?

Definition and Examples

Uniform vs Non-Uniform

Ancient Indian Alloys

3. Is Air a Mixture?

Composition and Activity

Dust in Air

4. Types of Mixtures

Classification

5. Pure Substances

Definition

Types

6. Elements

7. Compounds

8. Uses of Elements, Compounds, and Mixtures

9. What Are Minerals?

10. Snapshots

Key Concepts and Definitions

Mixture

Uniform Mixture

Non-Uniform Mixture

Pure Substance

Element

Compound

Important Facts and Figures

Questions and Answers from Chapter

Short Questions

Q1. Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

Q2. Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.

Q3. In which of the following cases are all the examples correctly matched?

Q4. Iron reacts with moist air to form iron oxide, and magnesium burns in oxygen to form magnesium oxide. Classify all the substances involved.

Q5. Classify the following as elements, compounds, or mixtures: Carbon dioxide, sand, seawater.

Q6. What new substance is formed when a mixture of iron filings and sulfur powder is heated?

Q7. Is it possible for a substance to be classified as both an element and a compound?

Q8. How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?

Q9. Analyze Fig. 8.24. Identify Gas A.

Q10. Write the names of any two compounds made only from non-metals.

Q11. How can gold be classified as both a mineral and a metal?

Q12. What is a mixture?

Q13. What is air's composition?

Q14. What are alloys?

Q15. What are elements?

Medium Questions

Q1. 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?

Q2. Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

Q3. Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.

Q4. In which of the following cases are all the examples correctly matched? Give reasons in support of your answers.

Q5. 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.

Q6. 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.

Q7. 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.

Q8. Is it possible for a substance to be classified as both an element and a compound? Explain why or why not.

Q9. How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?

Q10. Analyze Fig. 8.24. Identify Gas A. Also, write the word equation of the chemical reaction.

Q11. Write the names of any two compounds made only from non-metals, and also mention two uses of each of them.

Q12. How can gold be classified as both a mineral and a metal?

Q13. What is air a mixture?

Q14. What are types of mixtures?

Q15. What are pure substances?

Long Questions

Q1. 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?

Q2. Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

Q3. Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.

Q4. In which of the following cases are all the examples correctly matched? Give reasons in support of your answers.

Q5. 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.

Q6. 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.

Q7. 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.

Q8. Is it possible for a substance to be classified as both an element and a compound? Explain why or why not.