IS MATTER AROUND US PURE? in 1 Shot | FULL Chapter Coverage (Concepts + PYQs) | Class-9th Chemistry

Physics Wallah Foundation・2 minutes read

Pure substances are homogeneous in nature and cannot be separated into other types of matter by physical processes. Matter consists of particles or atoms that cannot be broken down into simpler substances, and understanding the characteristics of pure substances helps classify them into elements and compounds.

Insights

  • 1. Pure substances are homogeneous materials with distinct properties that cannot be separated into other types of matter through physical processes, further classified into elements and compounds based on their composition and characteristics.
  • 2. Elements are fundamental forms of matter that cannot be broken down into simpler substances by chemical reactions, while compounds consist of different elements chemically combined in fixed proportions by mass, showcasing unique properties distinct from their constituent elements.
  • 3. Understanding the differences between physical and chemical changes is crucial, where physical changes alter the state, size, or shape of a substance without forming new substances, while chemical changes lead to the creation of new substances with altered identities, often irreversible in nature.

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Recent questions

  • What are pure substances?

    Pure substances are materials without adulteration, like milk.

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Summary

00:00

Characteristics of Pure Substances: Elements and Compounds

  • Pure substances are those without any adulteration, like pure milk or ghee.
  • Pure substances are made up of only one kind of particles, such as gold particles in gold.
  • Pure substances are homogeneous in nature and have a definite set of properties.
  • Pure substances cannot be separated into other types of matter by physical processes.
  • Pure substances can be further classified into elements and compounds.
  • Elements are forms of matter that cannot be broken down into simpler substances by chemical reactions.
  • Compounds are made up of different elements chemically combined.
  • Mixtures can be classified into homogeneous and heterogeneous mixtures.
  • Matter can be classified based on chemical properties into pure substances and mixtures.
  • Understanding the characteristics of pure substances helps in classifying them into elements and compounds.

15:17

Elements, Compounds, and the Periodic Table

  • Matter consists of particles or atoms that cannot be broken down into simpler substances, such as gold, copper, and iron.
  • Water is considered a pure substance and can be broken down into simpler substances through a chemical process called Electrolysis, resulting in H2 and O2.
  • Water is not an element but a compound, as it is made up of hydrogen and oxygen atoms chemically combined.
  • Water is a pure substance composed of H2O molecules, making it a compound and not an element.
  • Elements can be classified into metals, nonmetals, and metalloids based on their properties, with examples like gold, silver, mercury, and bromine.
  • The periodic table displays elements classified into metals, nonmetals, and metalloids, with metals being solid, liquid, or gaseous substances.
  • Metals are malleable, ductile, sonorous, good conductors of heat and electricity, and have a lustrous appearance, like gold, copper, and aluminum.
  • Nonmetals, on the other hand, are brittle, not malleable or ductile, poor conductors of heat and electricity, and lack a lustrous appearance.
  • Metalloids have properties intermediate between metals and nonmetals, such as boron, silicon, germanium, and arsenic.
  • Compounds are substances made up of two or more elements chemically combined in fixed proportions by mass, like water being a compound of hydrogen and oxygen atoms.

29:44

Chemical Compounds: Fixed Mass Proportions in Formation

  • Compounds are formed by the combination of chemicals in fixed proportions by mass.
  • Water, for example, is composed of hydrogen and oxygen in a 1:8 ratio by mass.
  • The mass of one hydrogen atom is 1, while one oxygen atom is 16.
  • The simplified mass ratio of hydrogen to oxygen in water is 1:8.
  • Compounds must maintain fixed proportions by mass for their formation.
  • Carbon dioxide, made of carbon and oxygen, follows a 3:8 mass ratio.
  • Compounds differ from their constituent elements in properties.
  • Hydrogen is a non-combustible gas, while oxygen supports combustion.
  • Water extinguishes fire, showcasing compound properties.
  • Mixtures consist of elements or compounds not chemically combined, like air.

43:41

Distinguishing Mixtures: Homogeneous vs Heterogeneous

  • A heterogeneous mixture can be distinguished by its visible boundary of separation between different substances.
  • Homogeneous mixtures appear uniform and indistinguishable, while heterogeneous mixtures allow for the separation of components.
  • Examples of heterogeneous mixtures include sand and water, where sand and water can be visibly separated.
  • The distinction between homogeneous and heterogeneous mixtures lies in the ability to differentiate substances within the mixture.
  • Compounds are formed by the chemical combination of elements, creating new substances with fixed compositions.
  • Mixtures, on the other hand, involve the physical mixing of elements without forming new compounds.
  • Mixtures can have variable compositions, allowing for different ratios of components within the mixture.
  • Mixtures exhibit the properties of their individual components, while compounds have distinct properties from their constituents.
  • Mixtures can be separated using physical methods like filtration or evaporation, while compounds require chemical methods for separation.
  • Alloys, despite being unable to be separated into components by physical methods, are considered mixtures due to their variable compositions and property display.

58:54

Distinguishing Suspensions, Colloids, and Solutions

  • Suspensions are unstable, while colloids are stable.
  • Filtration separates salt and water, with salt remaining on top and water coming down due to particle size.
  • Filtration cannot separate solutions with very small particles passing through filter paper.
  • Colloids have particles larger than in solutions but smaller than in suspensions, leading to a homogeneous appearance.
  • Colloids consist of dispersed phase (solute-like component) and dispersion medium (solvent-like component).
  • Examples of colloids include aerosols (liquid dispersed in gas) and emulsions (liquid dispersed in liquid).
  • Solutions do not show the Tyndall effect, which is the scattering of light by suspended particles in colloids and suspensions.
  • The Tyndall effect can be observed in mist, where tiny water droplets act as colloidal particles.
  • Concentration of a solution is the amount of solute in a given volume of solution, determining if it is concentrated or diluted.
  • Formulas for calculating concentration include mass by mass percentage, mass by volume percentage, and volume by volume percentage.

01:13:44

Understanding Saturated and Unsaturated Solutions

  • Saturated solution concept explained: A solution where no more solute can dissolve at a specific temperature is termed a saturated solution.
  • Example of creating a saturated solution: Taking water at 20°C, adding 10 teaspoons of salt, and observing that no more salt can dissolve beyond 10 teaspoons.
  • Definition of an unsaturated solution: A solution where more solute can still be dissolved.
  • Example of an unsaturated solution: Adding one teaspoon of salt at a time until the solution can dissolve more salt, unlike a saturated solution.
  • Effect of temperature on a saturated solution: Increasing temperature causes particles to spread, creating space for more solute to dissolve, converting a saturated solution to unsaturated.
  • Effect of decreasing temperature: Lowering temperature causes particles to come closer, reducing space for solute, leading to solute separating out, converting a saturated solution to unsaturated.
  • Solubility definition: The maximum amount of solute that can dissolve in 100 grams of solvent at a specified temperature.
  • Example of solubility calculation: Taking 100 grams of water at 20°C and dissolving a maximum of 40 grams of salt in it.
  • Solubility changes with temperature: Solubility generally increases with increasing temperature and decreases with decreasing temperature.
  • Differentiating physical and chemical changes: Physical changes involve alterations in state, size, or shape without forming new substances, like melting ice or tearing paper.

01:27:10

"Physical vs. Chemical Changes in Substances"

  • Physical changes involve no new substances being formed, with substances retaining their identity.
  • Physical changes can be easily reversed through physical processes.
  • Changes in physical state, size, and shape of a substance are considered physical changes.
  • Chemical changes result in the formation of new substances, altering the identity of the original substances.
  • Chemical changes are generally irreversible, with new substances unable to return to their original form.
  • Examples of chemical changes include the burning of magnesium ribbon, producing magnesium oxide.
  • The burning of magnesium wire results in the formation of magnesium oxide, a new substance.
  • The rusting of iron is another example of a chemical change, forming a new substance.
  • The burning of a candle involves both physical and chemical changes, with wax melting as a physical change and the burning wick leading to the formation of new substances.
  • Understanding the properties of substances in different groups, such as metals, nonmetals, and metalloids, helps identify their characteristics and conductivities.

01:41:39

Chemical and Physical Changes in Solutions

  • Water and glucose are discussed, with the correct order being 150 first and then 100.
  • Physical changes involve alterations in physical properties without the formation of new substances.
  • Chemical changes result in the creation of new substances, with examples provided.
  • Elements like mercury and bromine exist in a liquid state at room temperature.
  • Tincture of iodine consists of iodine as the solute and alcohol as the solvent.
  • Differences in properties between solutions, colloids, and suspensions are due to varying particle sizes.
  • Mass by mass sugar solution involves 10 grams of sugar in a 100-gram solution, with water as the solvent.
  • Ramesh mistakenly used 90 grams of water instead of 100, while Sarika correctly prepared the solution with 10 grams of sugar and 90 grams of water.
  • Concentration calculations show Sarika's solution to have a higher mass percentage than Ramesh's due to the correct proportions used.
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