NCERT Gist: Is Matter Around us Pure? | Additional Study Material for UPSC PDF Download

- A mixture contains more than one substance (element and/or compound) mixed in any proportion.
- Mixtures can be separated into pure substances using appropriate separation techniques.
- A solution is a homogeneous mixture of two or more substances. The major component of a solution is called the solvent, and the minor, the solute.
- The concentration of a solution is the amount of solute present per unit volume or per unit mass of the solution/solvent.
- Materials that are insoluble in a solvent and have particles that are visible to naked eyes, form a suspension.
- A suspension is a heterogeneous mixture.

Colloids

- Are heterogeneous mixtures in which the particle size is too small to be seen with the naked eye, but is big enough to scatter light.
- Useful in industry and daily life.
- The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium.
- Pure substances can be elements or compounds.
- An element is a form of matter that cannot be broken down by chemical reactions into simpler substances.
- A compound is a substance composed of two or more different types of elements, chemically combined in a fixed proportion.
- Properties of a compound are different from its constituent elements, whereas a mixture shows the properties of its constituting elements or compounds.
- Mixtures are constituted by more than one kind of pure form of matter, known as a substance.
- A substance cannot be separated into other kinds of matter by any physical process which contains more than one substance.
- Mixture which has a uniform composition throughout. Such mixtures are called homogeneous mixtures or solutions.
- Some other examples of such mixtures are: (i) salt in water and (ii) sugar in water.
- A homogeneous mixture can have a variable composition.
- Mixtures, which contain physically distinct parts and have non-uniform compositions.
- Such mixtures are called heterogeneous mixtures.
- Mixtures of sodium chloride and iron filings, salt and sulphur, and oil and water are examples of heterogeneous mixtures.

Alloys

- Homogeneous mixtures of metals and cannot be separated into their components by physical methods.

- Considered as a mixture because it shows the properties of its constituents and can have variable composition.

- For example, brass is a mixture of approximately 30% zinc and 70% copper.

- A solution has a solvent and a solute as its components.

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Properties of a Solution

- A solution is a homogeneous mixture.
- The particles of a solution are smaller than 1 did (10 -9 metre) in diameter.
- Cannot be seen by naked eyes.
- Because of very small particle size, they do not scatter a beam of light passing through the solution.
- The path of light is not visible in a solution.

The Solute Particles

- Cannot be separated from the mixture by the process of filtration.
- Do not settle down when left undisturbed, that is, a solution is stable.
- When no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.
- The amount of the solute present in the saturated solution at this temperature is called its solubility.
- If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution.
- A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.
- Particles of a suspension are visible to the naked eye.

Properties of a Suspension

- Suspension is a heterogeneous mixture.
- The particles of a suspension can be seen by the naked eye.
- The particles of a suspension scatter a beam of light passing through it and make its path visible.
- The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable.
- They can be separated from the mixture by the process of filtration, a colloidal solution is a heterogeneous mixture, for example, milk.

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Properties of a Colloid

- A colloid is a heterogeneous mixture.
- The size of particles of a colloid is too small to be individually seen by naked eyes.
- Colloids are big enough to scatter a beam of light passing through it and make its path visible.
- They do not settle down when left undisturbed, that is, a colloid is quite stable.
- They cannot be separated from the mixture by the process of filtration.
- But, a special technique of separation known as centrifugation can be used to separate the colloidal particles.
- Some examples of solids which sublime are ammonium chloride, camphor, naphthalene and anthracene. Process of separation of components of a mixture is known as chromatography.
- Chromatography is the technique used for separation of those solutes that dissolve in the same solvent

Applications

- To separate • colours in a dye • pigments from natural colours • drugs from blood, distillation.
- It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.
- The crystallisation method is used to purify solids.
- Crystallisation technique is better than simple evaporation technique as -
- Some solids decompose or some, like sugar, may get charred on heating to dryness.
- Some impurities may remain dissolved in the solution even after filtration.
- On evaporation these contaminate the solid.
- The properties that can be observed and specified like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc. are the physical properties.

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Pure Substances Elements

- Element as a basic fonn of matter that cannot be broken down into simpler substances by chemical reactions.
- Divided into metals, non-metals and metalloids.
- Show some or all of the following properties:
- Have a lustre (shine).
- Have silvery-grey or golden-yellow colour.
- Conduct heat and electricity.
- Are ductile (can be drawn into wires).
- Are malleable (can be hammered into thin sheets).
- Are sonorous (make a ringing sound when hit).
- Mercury is the only metal that is liquid at room temperature.
- Non-metals usually show some or all of the following properties:
- They display a variety of colours.
- They are poor conductors of heat and electricity.
- They are not lustrous, sonorous or malleable.
- Examples of non-metals are hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine etc.
- A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion.