Composition of Matter | Class 8 | Science | Chapter 6 | Maharashtra State Board
Explore essential concepts in matter and its classification, including states of matter, intermolecular forces, and properties like incompressibility. Learn how mixtures, compounds, and elements are differentiated by their chemical composition, with examples in everyday items like milk and water.
Questions & Answers
1. Choose the appropriate option and rewrite the following statements.
a. The intermolecular force is ........ in the particles of solid.
i. minimum
ii. moderate
iii. Maximum
iv. indefinite
Ans. The intermolecular force is maximum in the particles of a solid.
b. Solids retain their volume even when external pressure is applied. This property is called ........ .
i. plasticity
ii. Fluidity
iii. incompressibility
iv. elasticity
Ans. Solids retain their volume even when external pressure is applied. This property is called incompressibility.
c. Matter is classified into the types mixture, compound and element, by applying the criterion ........ .
i. states of matter
ii. phases of matters
iii. chemical composition of matter
iv. all of these
Ans. Matter is classified into the types mixture, compound, and element by applying the criterion chemical composition of matter.
d. Matter that contain two or more constituent substances is called ........ .
i. mixture
ii. compound
iii. Element
iv. Metalloid
Ans. Matter that contains two or more constituent substances is called a mixture.
e. Milk is an example of type of matter called ........ .
i. solution
ii. homogeneous mixture
iii. heterogeneous mixture
iv. suspension
Ans. Milk is an example of a type of matter called a heterogeneous mixture.
f. Water, mercury and bromine are similar to each other, because three are ........ .
i. liquids
ii. compounds
iii. Non-metals
iv. elements
Ans. Water, mercury, and bromine are similar to each other because they are liquids.
g. Valency of carbon is 4 and that of oxygen is 2. From this, we understand that there are ...... chemical bond/bonds between the carbon atom and one oxygen atom in the compound-carbon dioxide.
i. 1
ii. 2
iii. 3
iv. 4
Ans. The valency of carbon is 4 and that of oxygen is 2. From this, we understand that there are 2 chemical bonds between the carbon atom and one oxygen atom in the compound carbon dioxide.
2. Identify the odd term out and explain.
a. Gold, silver, copper, brass
Ans.
Brass.
Gold, silver, and copper are pure elements, whereas brass is an alloy (a mixture of copper and zinc).
b. Hydrogen, hydrogen peroxide, carbon dioxide, water vapour.
Ans.
Hydrogen peroxide.
Hydrogen, carbon dioxide, and water vapour are common gases, while hydrogen peroxide is a chemical compound often found in liquid form and used as an antiseptic.
c. Milk, lemon juice, carbon, steel.
Ans.
Carbon.
Milk, lemon juice, and steel are mixtures, whereas carbon is an element.
d. Water, mercury, bromine, petrol.
Ans.
Petrol.
Water, mercury, and bromine are liquids at room temperature and have natural forms, while petrol is a processed mixture used as fuel.
e. Sugar, salt, baking soda, blue vitriol.
Ans.
Blue vitriol.
Sugar, salt, and baking soda are commonly used household substances, while blue vitriol (copper sulfate) is more specialized and often used in laboratories or agriculture.
f. Hydrogen, sodium, potassium, carbon.
Ans.
Carbon.
Hydrogen, sodium, and potassium are metals, whereas carbon is a non-metal.
3. Answer the following question.
a. Plants synthesize glucose in sunlight with the help of chlorophyll from carbon dioxide and water and give away oxygen. Identify the four compounds in this process and name their types.
Ans.
In the process of photosynthesis, the four compounds are:
1. Glucose (C₆H₁₂O₆) - A compound formed by the reaction, categorized as a carbohydrate.
2. Carbon dioxide (CO₂) - A compound that plants use as a raw material, categorized as a gas.
3. Water (H₂O) - Another reactant used by plants, categorized as a liquid.
4. Oxygen (O₂) - A compound released as a byproduct, categorized as a gas.
b. In one sample of brass, the following ingredients were found : copper (70%) and zinc (30%). Identify the solvent, solute and solution from these.
Ans.
In the brass alloy:
Solvent: Copper, as it makes up the larger percentage (70%).
Solute: Zinc, as it is present in a smaller proportion (30%).
Solution: Brass itself, as it is a homogeneous mixture of copper and zinc.
c. Sea water tastes salty due to the dissolved salt. The salinity (the proportion of salts in water) of some water bodies Lonar lake - 7.9 %, Pacific Ocean 3.5 % , Mediterranean sea - 3.8 %, Dead sea - 33.7 %. Explain two characteristics of mixtures from the above information.
Ans.
Two characteristics of mixtures illustrated by the salinity of different water bodies:
1. Variable Composition: The salinity varies significantly across different bodies of water (e.g., Lonar Lake at 7.9%, Pacific Ocean at 3.5%, Mediterranean Sea at 3.8%, Dead Sea at 33.7%), showing that mixtures can have different proportions of their components.
2. Retention of Properties: Each water body's taste (salty) is due to the dissolved salt, indicating that the individual properties of components (salty taste from salt) are retained in a mixture.
4. Give two examples each
a. Liquid element
Ans.
Mercury (Hg)
Bromine (Br₂)
b. Gaseous element
Ans.
Oxygen (O₂)
Nitrogen (N₂)
c. Solid element
Ans.
Iron (Fe)
Carbon (C)
d. Homogeneous mixture
Ans.
Salt water
Air
e. Colloid
Ans.
Milk
Fog
f. Organic compound
Ans.
Glucose (C₆H₁₂O₆)
Methane (CH₄)
g. Complex compound
Ans.
Hemoglobin (contains iron)
Chlorophyll (contains magnesium)
h. Inorganic compound
Ans.
Sodium chloride (NaCl)
Water (H₂O)
i. Metalloid
Ans.
Silicon (Si)
Boron (B)
j. Element with valency 1
Ans.
Hydrogen (H)
Sodium (Na)
k. Element with valency 2
Ans.
Oxygen (O)
Magnesium (Mg)
5. Write the names and symbols of the constituent elements and identify their valencies from the molecular formulae given below.
KCl, HBr, MgBr2 , K2 O, NaH, CaCl2 , CCl4 , HI, H2 S, Na2 S, FeS, BaCl2
Ans.
KCl
Elements: Potassium (K), Chlorine (Cl)
Valencies: Potassium = 1, Chlorine = 1
HBr
Elements: Hydrogen (H), Bromine (Br)
Valencies: Hydrogen = 1, Bromine = 1
MgBr₂
Elements: Magnesium (Mg), Bromine (Br)
Valencies: Magnesium = 2, Bromine = 1
K₂O
Elements: Potassium (K), Oxygen (O)
Valencies: Potassium = 1, Oxygen = 2
NaH
Elements: Sodium (Na), Hydrogen (H)
Valencies: Sodium = 1, Hydrogen = 1
CaCl₂
Elements: Calcium (Ca), Chlorine (Cl)
Valencies: Calcium = 2, Chlorine = 1
CCl₄
Elements: Carbon (C), Chlorine (Cl)
Valencies: Carbon = 4, Chlorine = 1
HI
Elements: Hydrogen (H), Iodine (I)
Valencies: Hydrogen = 1, Iodine = 1
H₂S
Elements: Hydrogen (H), Sulfur (S)
Valencies: Hydrogen = 1, Sulfur = 2
Na₂S
Elements: Sodium (Na), Sulfur (S)
Valencies: Sodium = 1, Sulfur = 2
FeS
Elements: Iron (Fe), Sulfur (S)
Valencies: Iron = 2, Sulfur = 2
BaCl₂
Elements: Barium (Ba), Chlorine (Cl)
Valencies: Barium = 2, Chlorine = 1
6. Chemical composition of some matter is given in the following table. Identify the main type of matter from their.
Ans.
Name of Matter | Chemical composition | Main type of matter |
Sea water | H₂O + NaCl + MgCl₂ + ... | Mixture |
Distilled water | H₂O | Compound |
Hydrogen gas filled in a balloon | H₂ | Element |
The gas in LPG cylinder | C₄H₁₀ + C₃H₈ | Mixture |
Baking soda | NaHCO₃ | Compound |
Pure gold | Au | Element |
The gas in oxygen cylinder | O₂ | Element |
Bronze | Cu + Sn | Mixture (Alloy) |
Diamond | C | Element |
Heated white powder of blue vitriol | CuSO₄ | Compound |
Limestone | CaCO₃ | Compound |
Dilute hydrochloric acid | HCl + H₂O | Mixture |
7. Write scientific reason.
a. Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish fire.
Ans.
Hydrogen is flammable and burns in the presence of oxygen, which supports combustion. However, water is a stable compound formed by hydrogen and oxygen, and it lacks the reactive properties of its elements. Additionally, water cools down the burning material, lowering the temperature and extinguishing fire.
b. Constituent substances of a colloid cannot be separated by ordinary filtration.
Ans.
In a colloid, the dispersed particles are very fine and small, typically between 1 and 1000 nanometers. These particles are too small to be trapped by ordinary filter paper, making standard filtration ineffective for separating them.
c. Lemon sherbat has sweet, sour, and salty taste, and it can be poured into a glass.
Ans.
Lemon sherbat is a homogeneous mixture containing sugar (sweet), lemon juice (sour), and salt. The mixture retains the flavors of each component and, being primarily liquid, it can flow and be poured easily.
d. A solid matter has the properties of definite shape and volume.
Ans.
In solids, particles are tightly packed in a fixed arrangement with strong intermolecular forces, allowing only slight vibration in place. This fixed structure gives solids a definite shape and volume, unlike liquids or gases.
8. Deduce the molecular formulae of the compound obtained from the following
a. C (Valency 4) & Cl (Valency 1)
Ans.
Cross Multiplication: Carbon (C) has a valency of 4, and Chlorine (Cl) has a valency of 1.
Formula: By cross-multiplying the valencies, we get CCl₄.
b. N (Valency 3) & H (Valency 1)
Ans.
Cross Multiplication: Nitrogen (N) has a valency of 3, and Hydrogen (H) has a valency of 1.
Formula: By cross-multiplying the valencies, we get NH₃.
c. C (Valency 4) & O (Valency 2)
Ans.
Cross Multiplication: Carbon (C) has a valency of 4, and Oxygen (O) has a valency of 2.
Formula: By cross-multiplying the valencies, we simplify the formula to CO₂.
d. Ca (Valency 2) & O (Valency 2)
Ans.
Cross Multiplication: Calcium (Ca) has a valency of 2, and Oxygen (O) has a valency of 2.
Formula: By cross-multiplying the valencies, the simplest formula is CaO.
E X T R A
1. Rewrite the sentences after filling the blanks:
1. ………….. have no definite shape, but have a definite volume.
Ans. Liquids have no definite shape, but have a definite volume.
2. ………… have neither a definite shape nor a definite volume.
Ans. Gases have neither a definite shape nor a definite volume.
3. The properties of a …………… are different than those of the constitute elements.
Ans. The properties of a compound are different than those of the constitute elements.
4. The part of matter having uniform composition is called ………………. .
Ans. The part of matter having uniform composition is called phase.
5. The heterogeneous mixture of a liquid and a solid is called a ……………. .
Ans. The heterogeneous mixture of a liquid and a solid is called a suspension.
6. A colloid is a ………………. mixture .
Ans. A colloid is a heterogeneous mixture.
7. Bronze contains atoms of the elements ……………. and ………….. .
Ans. Bronze contains atoms of the elements copper and tin.
8. When all the components of a mixture form one phase, it is called ………….. mixture.
Ans. When all the components of a mixture form one phase, it is called homogeneous mixture.
9. …………… is a mixture of water, lactose, fats and proteins.
Ans. Milk is a mixture of water, lactose, fats and proteins.
10. The intermolecular force is …………….. in the gaseous state.
Ans. The intermolecular force is very weak in the gaseous state.
2. Choose the appropriate option and rewrite the following statements:
1. When a liquid is poured from one container to another, its shape may change, but its volume ………….. .
(a) increases
(b) decreases
(c) remains the same
(d) none of them
Ans.
When a liquid is poured from one container to another, its shape may change, but its volume remains the same.
2. The property by which some solids maintain their shape even when subjected to external forces is called ………. .
(a) elasticity
(b) fluidity
(c) rigidity
(d) plasticity
Ans.
The property by which some solids maintain their shape even when subjected to external forces is called rigidity.
3. …………… is a complex compound.
(a) Glucose
(b) Blue vitriol
(c) Chlorophyll
(d) Soda
Ans.
Chlorophyll is a complex compound.
4. ………….. is a homogeneous mixture.
(a) Sand + water
(b) Flour + water
(c) Salt + water
(d) Oil + water
Ans.
Salt + water is a homogeneous mixture.
3. State whether the following statements are True or False:
1. Liquids do not have a definite shape.
Ans. True.
2. Gases have a definite shape and volume.
Ans. False. (Gases do not have shape and volume.)
3. The crystals of blue vitriol form a single phase.
Ans. True.
4. Water is a mixture.
Ans. False. (Water is a compound)
5. Milk is a colloid.
Ans. True.
6. A suspension does not scatters light.
Ans. True.
7. Copper sulphate is a mixture.
Ans. False. (Copper sulphate is a compound.)
8. An atom forms as many chemical bonds with other atom as its valency.
Ans. True.
9. The strength of intermolecular forces is weak in the liquid state.
Ans. False. (The strength of intermolecular forces is moderate in the liquid state.)
10. All the gases present together constitute a single phase.
Ans. True.
4. Answer the following questions in one sentence:
1. Why does a solid have definite volume?
Ans. A solid has a definite volume because its particles are closely packed in a fixed, orderly arrangement, limiting their movement.
2. Why does a liquid have indefinite shape?
Ans. A liquid has an indefinite shape because its particles can move past each other, allowing it to take the shape of its container.
3. Why does a gas have indefinite volume and shape?
Ans. A gas has indefinite volume and shape because its particles move freely and spread out to fill the entire available space.
4. What can you say about the distance between the neighboring particles of a solid?
Ans. The distance between neighboring particles of a solid is very small, as they are tightly packed.
5. What can you say about the distance between the constituent particles of a gas?
Ans. The distance between the constituent particles of a gas is large, as they are spread far apart.
6. State whether the mixture of oil in water is a homogeneous or heterogeneous mixture.
Ans. The mixture of oil in water is a heterogeneous mixture.
7. State whether seawater is a homogeneous or heterogeneous mixture.
Ans. Seawater is a homogeneous mixture.
8. Give two examples of liquid in liquid.
Ans. Alcohol in water and vinegar in water.
9. Give two examples of gas in gas.
Ans. Oxygen in nitrogen (air) and carbon dioxide in air.
10. Give two examples of solid in solid.
Ans. Brass (copper and zinc) and steel (iron and carbon).
11. Give two examples of gas in liquid.
Ans. Carbon dioxide in soda water and oxygen in water.
12. Give molecular formulae of:
Ans.
Potassium chloride: KCl
Sodium sulfide: Na₂S
13. State the molecular formula and number of hydrogen atoms in methane.
Ans. The molecular formula of methane is CH₄, and it contains 4 hydrogen atoms.
14. Identify the valency of chlorine in:
Ans.
(i) KCl: Chlorine has a valency of 1.
(ii) CaCl₂: Chlorine has a valency of 1.
5. Answer the following:
1. State two principal ways of classifying matter.
Ans. Matter can be classified based on its physical state (solid, liquid, and gas) and chemical composition (element, compound, and mixture).
2. What are the different states of matter?
Ans. The different states of matter are solid, liquid, and gas.
3. Define solid.
Ans. A solid is a state of matter with a definite shape and volume due to the tightly packed arrangement of its particles.
4. State any three characteristics of solids.
Ans. Solids have a definite shape and volume, high density, and are rigid and incompressible.
5. What is meant by rigidity of solids?
Ans. Rigidity of solids refers to their ability to maintain a fixed shape without easily deforming when a force is applied.
6. What is meant by elasticity of solids?
Ans. Elasticity of solids is the property that allows them to return to their original shape after the removal of a deforming force.
7. What is meant by plasticity?
Ans. Plasticity is the property of a material that enables it to undergo permanent deformation without breaking when a force is applied.
8. Solids have a high density and negligible compressibility. Explain.
Ans. Solids have high density because their particles are closely packed together, and they are negligibly compressible as there is little to no space between particles to allow compression.
9. Define liquid.
Ans. A liquid is a state of matter that has a definite volume but no definite shape, taking the shape of its container due to loosely packed particles that can move past each other.
10. State any three characteristics of liquids.
Ans. Liquids have definite volume but indefinite shape, fluidity, and are slightly compressible.
11. What is meant by fluidity?
Ans. Fluidity is the ability of a substance to flow and take the shape of its container, a characteristic property of liquids and gases.
12. Liquids have fluidity and they do not have a definite shape. Explain.
Ans. Liquids have fluidity, which allows their particles to move past each other, resulting in an indefinite shape as they take the shape of their container.
13. Define gas.
Ans. A gas is a state of matter that has neither a definite shape nor a definite volume, with particles that move freely and fill the entire space available.
14. State any three characteristics of gases.
Ans. Gases have indefinite shape and volume, low density, and are highly compressible.
15. Gases have neither a definite shape nor a definite volume. Explain.
Ans. The particles in gases are widely spaced and move freely, allowing them to expand and fill any container, resulting in no definite shape or volume.
16. Why are gases more compressible than liquids?
Ans. Gases are more compressible than liquids because there is a large amount of space between gas particles, allowing them to be pushed closer together under pressure.
17. What is an element? Give two examples.
Ans. An element is a pure substance made up of only one type of atom and cannot be broken down into simpler substances. Examples: Hydrogen (H) and Oxygen (O).
18. Write any two characteristics of an element.
Ans. Elements are composed of only one type of atom, and they have unique physical and chemical properties.
19. What is a compound? Give two examples.
Ans. A compound is a substance formed when two or more elements chemically combine in fixed proportions. Examples: Water (H₂O) and Carbon dioxide (CO₂).
20. Write any two characteristics of a compound.
Ans. Compounds have a fixed composition and distinct properties that differ from those of the individual elements that form them.
21. What is a mixture? Give two examples.
Ans. A mixture is a combination of two or more substances that are not chemically combined and retain their individual properties. Examples: Air and Saltwater.
22. Write any two characteristics of a mixture.
Ans. Mixtures have variable composition, and the components can be separated by physical methods.
23. Classify the following into elements, compounds, and mixtures:
Ans.
Elements: Sodium, Nitrogen, Mercury
Compounds: Sugar, Sodium carbonate, Sulphuric acid, Potassium dichromate
Mixtures: Air, Stainless steel, Cement
24. What is meant by an organic compound? Give two examples.
Ans. An organic compound is a compound primarily made of carbon atoms bonded with hydrogen and possibly other elements. Examples: Methane (CH₄) and Glucose (C₆H₁₂O₆).
25. What is meant by an inorganic compound? Give two examples.
Ans. An inorganic compound is a compound that does not primarily consist of carbon-hydrogen bonds. Examples: Water (H₂O) and Sodium chloride (NaCl).
26. What is meant by complex compounds? Give two examples.
Ans. Complex compounds are compounds where a central metal atom is surrounded by other atoms or molecules in a structured arrangement. Examples: Hemoglobin (contains iron) and Chlorophyll (contains magnesium).
27. Classify the following compounds into organic compounds, inorganic compounds, and complex compounds: Ans.
Organic compounds: Petrol, Cooking gas
Inorganic compounds: Common salt, Blue vitriol
Complex compounds: Hemoglobin, Cyanocobalamine
28. What is a phase?
Ans. A phase is a part of matter that has uniform composition and properties, such as solid, liquid, or gas in a mixture.
29. What is a homogeneous mixture? Give two examples.
Ans. A homogeneous mixture is a mixture with uniform composition throughout, where the components are indistinguishable. Examples: Air and Vinegar.
30. What is a heterogeneous mixture? Give two examples.
Ans. A heterogeneous mixture is a mixture with non-uniform composition, where the components are distinguishable. Examples: Oil in water and Sand in water.
31. Define solution or What is meant by a solution? Give two examples.
Ans. A solution is a homogeneous mixture of two or more substances, where one substance (solute) is dissolved in another (solvent). Examples: Saltwater and Sugar in water.
32. What is meant by a solvent? Give two examples.
Ans. A solvent is the component of a solution that dissolves the solute, usually present in a larger amount. Examples: Water and Alcohol.
33. What is meant by a solute? Give two examples.
Ans. A solute is the substance that is dissolved in a solvent to form a solution, usually present in a smaller amount. Examples: Salt and Sugar.
34. What is meant by a suspension?
Ans. A suspension is a heterogeneous mixture where solid particles are dispersed in a liquid or gas, but the particles are large enough to settle over time.
35. Define colloid.
Ans. A colloid is a heterogeneous mixture where fine particles of one substance are evenly dispersed within another, and the particles are small enough to remain suspended without settling.
36. State the characteristics of a solution.
Ans. Solutions have a uniform composition, do not scatter light, and cannot be separated by filtration.
37. State the characteristics of a suspension.
Ans. Suspensions are heterogeneous, scatter light, and the solid particles can settle over time and can be separated by filtration.
38. State the characteristics of a colloid.
Ans. Colloids are heterogeneous mixtures, scatter light (Tyndall effect), and the particles do not settle over time and cannot be separated by filtration.
39. Give two examples of each of the following:
Phase, Homogeneous matter, Heterogeneous matter, Homogeneous mixture, Heterogeneous mixture, Solution, Suspension, Colloid
Ans.
Phase: Solid ice, Liquid water
Homogeneous matter: Pure water, Pure air
Heterogeneous matter: Soil, Concrete
Homogeneous mixture: Saltwater, Sugar syrup
Heterogeneous mixture: Oil in water, Sand in water
Solution: Saltwater, Vinegar
Suspension: Muddy water, Flour in water
Colloid: Milk, Fog
40. State the different types of solutions. Give one example.
Ans. Types of solutions include solid in liquid (e.g., saltwater), liquid in liquid (e.g., alcohol in water), gas in gas (e.g., air), gas in liquid (e.g., carbon dioxide in soda).
41. Classify the following into homogeneous solution and heterogeneous solution:
Ans.
Homogeneous solution: Soda water, Potassium permanganate solution, Alcohol in water, Ink solution
Heterogeneous solution: Milk, Wheat flour in water
42. Classify the following into solution, suspension, and colloid:
Ans.
Solution: Lemonade, Oxygen in water
Suspension: Sand in water
Colloid: Milk, Smoke
43. What is meant by molecular formula?
Ans. A molecular formula represents the number and type of atoms present in a molecule of a compound, using symbols and subscripts.
44. What is meant by valency of an element?
Ans. Valency is the ability of an element's atom to combine with other atoms, determined by the number of electrons it can lose, gain, or share to achieve a stable electron configuration.
45. Deduce the molecular formulae of the compound obtained from the following pairs of elements by the cross multiplication method:
(a) C (Valency 4) & Cl (Valency 1)
(b) N (Valency 3) & H (Valency 1)
(c) C (Valency 4) & O (Valency 2)
(d) Ca (Valency 2) & O (Valency 2)
Ans.
(a) C (Valency 4) & Cl (Valency 1): CCl₄
(b) N (Valency 3) & H (Valency 1): NH₃
(c) C (Valency 4) & O (Valency 2): CO₂
(d) Ca (Valency 2) & O (Valency 2): CaO
Note: If you have any additional questions or feedback, please leave them in the comment section below. We will try to answer them and update this blog accordingly as soon as possible.
Comments