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Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

Pure Substances

  • Pure substances, like elements or compounds such as diamond or carbon dioxide, consist of a single type of entity and cannot be broken down further through chemical or physical methods. 
  • Elements, in particular, are pure materials made up of only one type of atom, ensuring consistency in composition and properties. 
  • These substances exhibit homogeneity, with constant boiling and melting points. 
  • In chemical reactions, pure substances play a role, producing predictable outcomes due to their stable nature.

Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

Mixtures

It is made up of two or more elements or compounds mixed in any ratio/proportion.

Properties

  • It may be homogeneous or heterogeneous.
  • The properties of constituent substances are retained.
  • No new compound is formed after mixing.
  • Constituents of a mixture can be separated by simple physical processes.
  • It does not have a fixed melting and boiling point.

Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

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Solution

A solution is a homogeneous mixture of two or more substances (e.g., Lemonade, soda water). 

Table: Difference between Solute and Solvent.

Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

Concentration of Solution

  • The amount of solute that has dissolved in a specific amount of solvent or solution is measured as solution concentration.
  •  A concentrated solution is one that has a significant amount of dissolved solute in it. 
  • A diluted solution is one that has a small amount of dissolved solute in it.

Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

Alloys

Alloys are homogeneous mixtures of metals or a mixture of a metal and another element that cannot be separated into their components by physical methods.

Examples:

  • Steel – a combination of iron (metal) and carbon (non-metal).
  • Bronze – a combination of copper (metal) and tin (metal).
  • Brass – a mixture of copper (metal) and zinc (metal).

Suspension

A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Ex: Chalk in water, smoke in the air


Properties of Suspension :

  1. It is a heterogeneous mixture.
  2. Particles of a suspension are visible to the naked eye.
  3. The size of the particles is greater than 100 nm.
  4. It is an unstable mixture. Solute settles down at the bottom over the period.
  5. If the solution is passed through filter paper, the solute and solvent get separated.
  6. It scatters light when light is passed through the solution i.e. it shows the Tyndall effect.


Colloidal Solution


A colloid solution is a heterogeneous mixture in which the size of particles lies between the true solutions and suspensions. 

  • Colloidal particles can easily scatter a beam of visible light. 
  • This phenomenon is called the Tyndall effect. 

Properties of Colloidal Solution:

  1. The particles of colloids can’t be seen by the naked eye individually.
  2. It is a heterogeneous mixture and thus solute and solvent can’t be separated by filter paper.
  3. The size of particles is smaller than suspensions but greater than solutions (1 nm to 100 nm).
  4. It is a stable mixture. Particles do not settle down at the bottom over a period of time.
  5. They do not settle down when left undisturbed which means colloid is quite stable. 

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Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

Physical and Chemical Change
Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

Types of Pure Substances

The pure substance is divided in two types based on their chemical composition:

(i)  Elements


  • According to Antoine Laurent Lavoisier, the element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
  • It is divided into three types which are metals, non-metals and metalloids.
Properties of Metals
  1. They have a lustre (shine).
  2. They have a silvery-grey or golden-yellow colour.
  3. They conduct heat and electricity.
  4. They are ductile (can be drawn into wires).
  5. They are malleable (can be hammered into thin sheets).
  6. They are sonorous (make a ringing sound when hit).
Examples: gold, silver, copper, iron, sodium, potassium etc. are Metals

Note: Mercury is the only metal that is liquid at room temperature.
Properties of non-metals
  1. They display a variety of colours.
  2. They are poor conductors of heat and electricity.
  3. They are not lustrous, sonorous or malleable.
Examples of non-metals are hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine etc.

Metalloids: Elements having intermediate properties between those of metals and non-metals are called metalloids.  Examples are boron, silicon, germanium etc.

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What is a solution?
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(ii) Compounds


A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion.

Characteristics

  • The properties of a compound differ from those of its constituents.
  • The compound has a fixed melting point and boiling point.
  • A compound is a homogeneous substance.
  • Constituent elements can be separated by chemical processes.
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FAQs on Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

1. What are the different types of pure substances?
Ans. Pure substances can be classified into two types: (i) Elements: These are substances that cannot be broken down into simpler substances by any chemical means. Examples of elements include hydrogen, oxygen, and carbon. (ii) Compounds: These are substances that are composed of two or more elements chemically combined in a fixed ratio. Examples of compounds include water (H2O) and sodium chloride (NaCl).
2. What is a solution and how is its concentration determined?
Ans. A solution is a homogeneous mixture composed of two or more substances. The concentration of a solution refers to the amount of solute (substance being dissolved) present in a given amount of solvent (substance doing the dissolving). Concentration can be determined by various methods, such as measuring the mass of the solute dissolved in a known volume of solvent (mass/volume percent), or by measuring the volume of the solute dissolved in a known volume of solvent (volume/volume percent). Other common units of concentration include molarity (moles of solute per liter of solution) and molality (moles of solute per kilogram of solvent).
3. What is a colloidal solution and how is it different from other types of solutions?
Ans. A colloidal solution, also known as a colloidal suspension, is a type of mixture in which small particles of one substance are dispersed evenly throughout another substance. The particles in a colloidal solution are larger than those in a true solution but smaller than those in a suspension. Unlike true solutions, colloidal solutions do not settle out upon standing and cannot be separated by filtration. Examples of colloidal solutions include milk, gelatin, and fog.
4. What is the difference between a physical change and a chemical change?
Ans. A physical change refers to a change in the physical properties of a substance without any change in its chemical composition. Examples of physical changes include changes in state (such as melting or boiling), changes in shape or size, and changes in solubility. On the other hand, a chemical change refers to a change in the chemical composition of a substance resulting in the formation of one or more new substances. Examples of chemical changes include combustion, rusting, and digestion.
5. Why is it important to study the purity of matter?
Ans. Studying the purity of matter is important for several reasons: - It helps in understanding the properties and behavior of substances. - It is crucial in fields like medicine, where impurities can affect the effectiveness and safety of drugs. - It plays a role in manufacturing industries, as impurities can impact the quality and performance of products. - It aids in environmental monitoring, as the presence of impurities in air, water, and soil can have harmful effects on ecosystems and human health. - It is essential in scientific research, where pure substances are often required for accurate experimentation and analysis.
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