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 substances without any adulteration, like gold or oxygen, with fixed properties and cannot be separated into other types of matter. Understanding the characteristics and classification of pure substances, compounds, elements, and mixtures is crucial in chemistry.

Insights

  • Pure substances are those without any adulteration, made up of only one kind of particles, homogeneous in nature, and have a definite set of properties.
  • Elements are forms of matter that cannot be broken down into simpler substances by chemical reactions, while compounds are substances made up of different elements chemically combined.
  • Mixtures can be classified into homogeneous and heterogeneous mixtures, with homogeneous mixtures having uniform composition and no visible boundary of separation, while heterogeneous mixtures exhibit visible distinctions and allow for the identification of substances within them.

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Recent questions

  • What are pure substances?

    Pure substances are materials without any adulteration, consisting of only one kind of particles with homogeneous properties. They cannot be separated into other types of matter by physical processes and are further classified into elements and compounds.

  • How are elements and compounds different?

    Elements are forms of matter that cannot be broken down into simpler substances by chemical reactions, while compounds are substances made up of different elements chemically combined. Elements are the building blocks of compounds, and understanding their characteristics is crucial in chemistry.

  • What is the difference between homogeneous and heterogeneous mixtures?

    Homogeneous mixtures have a uniform composition with no visible boundary of separation, like salt dissolved in water, while heterogeneous mixtures have visible distinctions, like sand in water. Homogeneous mixtures are indistinguishable, while heterogeneous mixtures allow for the identification of substances within them.

  • How are compounds separated from their constituent elements?

    Compounds can be separated into their constituent elements through chemical processes like electrolysis. Unlike mixtures, compounds have fixed compositions and properties different from their components, requiring chemical methods for separation.

  • What is the Tyndall effect?

    The Tyndall effect is the scattering of light by suspended particles, visible in colloids and suspensions but not in solutions. It can be observed in mist, forest canopies, and when sunlight passes through dense forests, aiding in the identification of colloids and suspensions.

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Summary

00:00

Characteristics and Classification of Pure Substances

  • 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 or oxygen.
  • 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 substances 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 and classification of pure substances is crucial in chemistry.

15:15

"Chemistry: Elements, Compounds, and Properties"

  • Gold is made only from gold atoms, which are a form of matter that cannot be broken down into simpler substances.
  • Water is considered a mystery in chemistry, but it is a pure substance composed of hydrogen and oxygen atoms.
  • The formula for water is H2O, and it can be broken down into simpler substances through a chemical process called Electrolysis.
  • Water is not an element but a compound, as it can be broken down into simpler substances through a chemical reaction.
  • Water is made up of only one kind of particle, H2O, making it a pure substance and not an element.
  • Elements can be classified into metals, nonmetals, and metalloids based on their properties.
  • The periodic table categorizes elements into metals, nonmetals, and metalloids, with examples like mercury and bromine being liquid elements at room temperature.
  • Metals are malleable, ductile, sonorous, good conductors of heat and electricity, and have a lustrous appearance.
  • Nonmetals, on the other hand, are brittle, not malleable or ductile, and are bad conductors of heat and electricity.
  • Metalloids have properties that are intermediate between metals and nonmetals, with examples like boron, silicon, and germanium.

29:39

Chemical compounds: fixed proportions, distinct properties.

  • Chemical combination occurs between elements to form compounds in fixed proportions by mass.
  • Water, composed of hydrogen and oxygen, exemplifies a compound with a fixed proportion of 1:8.
  • The mass of one hydrogen atom is 1, while one oxygen atom is 16, leading to a 1:8 ratio in water.
  • Compounds are substances made up of two or more elements chemically combined in fixed proportions by mass.
  • Compounds like carbon dioxide require elements to combine in specific ratios, such as 3:8 for carbon and oxygen.
  • Compounds can be separated into their constituent elements through chemical processes like electrolysis.
  • The properties of compounds differ from their constituent elements, with compounds like water extinguishing fire.
  • Mixtures consist of elements or compounds not chemically combined, like air with nitrogen, oxygen, and carbon dioxide.
  • Mixtures can be homogeneous, with uniform composition and no visible boundary of separation, or heterogeneous, with visible distinctions.
  • Homogeneous mixtures, like salt dissolved in water or tea, have indistinguishable components, while heterogeneous mixtures, like sand in water, have visible boundaries of separation.

43:32

Understanding Mixtures: Heterogeneous vs. Homogeneous

  • Heterogeneous mixtures allow for the identification and distinction of substances within them.
  • A heterogeneous mixture lacks a uniform composition and has visible boundaries separating its components.
  • Examples of heterogeneous mixtures include sand and water, where sand and salt can be visibly distinguished.
  • Homogeneous mixtures resemble each other and are indistinguishable, like tea or coffee.
  • Compounds are formed by elements combining chemically to create new substances, unlike mixtures.
  • Mixtures can have variable compositions, unlike compounds with fixed compositions.
  • Mixtures exhibit the properties of their components and can be separated by physical methods.
  • Compounds, on the other hand, have different properties from their components and require chemical methods for separation.
  • Alloys, mixtures of metals, cannot be separated into their components by physical methods and are considered mixtures due to their variable compositions and property display.
  • Brass, an alloy of zinc and copper, exemplifies a mixture with variable composition, approximately 30% zinc and 70% copper.

58:54

"Colloids, Suspensions, and Concentration in Solutions"

  • Suspensions are unstable, while colloids are stable.
  • Filtration separates substances based on particle size, with smaller particles passing through the filter paper.
  • Colloids have particles larger than those in solutions but smaller than those in suspensions.
  • Colloids consist of a dispersed phase (solute-like component) and a dispersion medium (solvent-like component).
  • Examples of colloids include aerosols (liquid dispersed in gas) and emulsions (liquid dispersed in liquid).
  • The Tyndall effect is the scattering of light by suspended particles, visible in colloids and suspensions but not in solutions.
  • The Tyndall effect can be observed in mist, forest canopies, and when sunlight passes through dense forests.
  • Concentration of a solution is the amount of solute in a given volume of solution.
  • Concentration can be calculated using formulas for mass by mass percentage, mass by volume percentage, and volume by volume percentage.
  • Understanding concentration is crucial for solving numerical problems related to solutions.

01:13:42

Solute Dissolution and Physical Changes Explained

  • Saturated solution is a solution where no more solute can dissolve at a specific temperature.
  • An example is given with water at 20°C where 10 teaspoons of salt are dissolved, and adding an 11th spoon shows no more dissolution.
  • Unsaturated solution is one where more solute can be dissolved, demonstrated by gradually adding salt until saturation is reached.
  • The effect of temperature on a saturated solution is explained, showing that increasing temperature leads to more solute dissolution.
  • Conversely, decreasing temperature causes solute to separate out of the solution.
  • Solubility is defined as the maximum amount of solute that can dissolve in 100 grams of solvent at a specified temperature.
  • Physical changes are described as alterations in state, size, or shape of a substance without creating a new substance.
  • Examples include breaking glass, tearing paper, and melting ice, where the substance remains the same despite the change.
  • The statement is made that changes in physical state, size, and shape constitute physical changes.
  • It is emphasized that physical changes do not result in the creation of new substances, only alterations in the existing material.

01:27:06

Chemical and Physical Changes Explained

  • Physical changes involve no new substances being formed, with substances retaining their identity.
  • Physical changes can be easily reversed through physical processes, such as changes in state, size, or shape.
  • Chemical changes result in the formation of new substances, altering the identity of the original substances.
  • Chemical changes are generally irreversible, leading to the creation of new substances that cannot return to their original form.
  • Examples like the burning of magnesium ribbon illustrate chemical changes, where magnesium transforms into magnesium oxide.
  • The burning of paper results in the creation of ash and smoke, showcasing a chemical change.
  • Rusting of iron exemplifies a chemical change, forming a new substance with properties intermediate between metals and nonmetals.
  • The burning of candles involves both physical and chemical changes, with wax melting as a physical change and the wick burning as a chemical change.
  • Understanding the properties of substances in different groups, like metals, nonmetals, and metalloids, aids in identifying chemical changes.
  • Practical questions, like determining the mass of water and glucose needed to create a glucose solution, test comprehension of chemical concepts and calculations.

01:41:36

Chemical and Physical Changes in Solutions

  • Respectively, water is discussed first, followed by glucose, with the correct answer being 150 and then 100.
  • Physical changes involve no new substance formation but changes in physical properties like shape and appearance.
  • Chemical changes result in new substances being formed, with examples provided.
  • Elements existing in liquid state at room temperature are Mercury and Bromine, with Mercury being a metal and Bromine a nonmetal.
  • Tincture of iodine contains 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 made a mistake by using 90 grams of water instead of 100, while Sarika correctly used 100 grams, resulting in a higher mass percentage.
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