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Mixture - Introduction

Matters can be classified into two types – Pure substances and Impure substances.

Pure substances – Pure substances are of two types – Elements and Compounds.

Impure substances – All mixture are considered as impure substances.

Matter-Classification

Most of the substances in our surroundings are not in their pure form and are called mixture. Substances which are made of two or more matters and which can be separated by physical methods are known as mixtures, such as mixture of salt and water, mixture of sugar and water, mixture of different gases, air, etc.
In a mixture, components do not combine chemically or through any chemical change. In a mixture, components do not lose their properties.
Mixtures are of two types on the basis of their composition - Homogeneous mixture and Heterogeneous mixture.

Homogeneous Mixture
Mixtures which have uniform composition throughout are called Homogeneous Mixture. For example – mixture of salt and water, mixture of sugar and water, air, lemonade, soda water, etc.
Mixture of salt in water is an example of homogeneous mixture. In this mixture, the boundary of salt and water cannot be differentiated. When a ray of light is passed through the mixture of salt and water, the path of light is not seen.

General Properties of Homogeneous Mixture:
1.All solutions are the examples of homogeneous mixture.
2.The particles of a homogeneous mixture are less the one nanometer.
3.A homogenous mixture does not show Tyndall effect.
4.The boundaries of particles cannot be differentiated.
5.The constituent particles of homogenous mixture cannot be separated using centrifugation or decantation.
6.Alloys are the examples of solution.

Heterogeneous Mixture
Mixtures which do not have uniform composition throughout are called Heterogeneous Mixture. For example – mixture of soil and sand, mixture of sulphur and iron fillings, mixture of oil and water etc. The boundaries of constituent particles of a homogeneous mixture can be identified easily; as a homogeneous mixture has two or more distinct phases.

General Properties of Heterogeneous Mixture:
1.Most of the mixtures are heterogeneous except solutions and alloys.
2.The constituent particles are present uniformly in a heterogeneous mixture.
3.The components of a heterogeneous mixture can be identified easily.
4.Generally, two or more phases are present in a heterogeneous mixture.
5.Particles of a heterogeneous mixture are sized between one nanometer and one micrometer or more.
6.Heterogeneous mixtures show Tyndall effect.

Types of Mixture
Mixture can be categorised in three types on the basis of their particles’ size. These are; solution, suspension and colloid.

Solution:
Mixture of two or more substances with one phase only, i.e. having no distinct boundary of constituent particles are called solution. For example, solution of sugar and water, solution of salt and water, lemonade, soft drinks, etc. Solution is a homogeneous mixture of two or more substances.
In a solution, components are mixed in such a way that they appear as only one phase. Seeing by naked eye, constituent particles of a solution cannot be identified because particles are mixed evenly throughout.

In a solution, there are two types of components – one is called solute and other is called solvent.

Solute – Substance which is present in smaller quantity in a mixture is called solute.

Solvent – Substance in a mixture which is present in larger quantity in a mixture is called solvent.
Example: In the solution of salt and water, salt is present in small quantity while water is present in larger quantity. Here salt is solute and water is solvent.
Solution of tincture iodine is made by dissolving iodine in alcohol. In this solution, iodine is solute and alcohol is solvent.
Air is mixture of many gases. Since air consists of only one phase, thus it is considered as solution. Air consists about 78% of nitrogen and 22% rest of other gases. Thus in the case of air, nitrogen can be called as solvent and rest other gases as solutes.
Solvent and solute can be solid, liquid or gas.

Types of solution

Solid - solid solution – Solution of two or more solids are generally known as solid-solid solution. For example – alloys. Alloy is a homogeneous mixture of two or more metals and non metals or two metals or two non-metals. The components of an alloy cannot be separated by physical methods, their boundaries are not distinct and they can have variable compositions, thus alloy is considered as solution.

Solid – Liquid solution – Solution of solid and liquid is called solid-liquid solution. For example - solution of salt and water.

Liquid – liquid solution – Solution of two miscible liquids are called liquid-liquid solution, such as solution of water and acetic acid. The solution of acetic acid in water is known as vinegar.

Gas - liquid solution  Solution of gas into liquid is called gas-liquid solution. For example – Soft drink. In soft drink, carbon dioxide is usually dissolved in liquid, because of which a hiss sound comes while opening the cap of the bottle.

Gas-gas solution – Solution of two or more gas is called gas-gas solution. For example – air, which is the solution of many gases, such as hydrogen, oxygen, carbon dioxide, etc.

General Characteristics of Solution:
1.Solutions are homogeneous mixture of two or more substances.
2.Constituent particles of a solution are mixed evenly throughout.
3.There is only one phase in a solution.
4.Boundaries of constituent particles cannot be distinguished.
5.The size of particles of solution is smaller than one nanometer.
6.Solutions do not show Tyndall effect, because, small particles of solution do not scatter the ray of light.
7.Solute cannot be separated by using filtration or decantation.
8.Solutions are stable, since when left undisturbed the particles do not settle in bottom.

Saturated and Unsaturated Solutions

Saturated Solution: When a solution cannot dissolve more solute at a given temperature, the point is called saturation point of the solution and solution is called saturated solution. This means, no more solute can be dissolved in a saturated solution at a given temperature.
Unsaturated Solution: Solution in which more solution can dissolved at a given temperature, is called unsaturated solution.

Solubility: Solubility is the amount of solute in a saturated solution at a given temperature. In other words, maximum capacity to dissolve a solute in a solution at a given temperature is called solubility.
Different solvents can dissolve different amount of solute. This means different solvents have different solubility Solubility increases with increase in temperature.

Concentration: Concentration is the amount of solute present in a given amount of solvent or solution.

mixture1

Thus, concentration is the ratio of amount of solute and amount of solvent.
Concentration can be expressed in mass percentage or volume percentage of a solution.

(a) Mass percentage of a solution

mixture2

This means when concentration is expressed in mass percentage, it is called concentration by mass percentage.

(b) Volume percentage of a solution

mixture3

This means when concentration is expressed in volume percentage, it is called concentration by volume percentage.

Suspension
Suspension is the heterogeneous mixture of two or more substances. In suspension, particles are suspended throughout in bulk and can be seen by naked eyes. In suspensions, particles of solute do not dissolve rather are suspended. Particles of suspension are large enough to scatter rays of light and path of ray is visible through a suspension.

Example of suspension – mixture of chalk and water, muddy water, mixture of flour and water, mixture of dust particles and air, fog, milk of magnesia, etc.

General Characteristics of Suspension:
1.Suspensions are heterogeneous mixture of two or more substances.
2.Particles of solute do not dissolve in solvent rather they remain suspended in bulk throughout.
3.The size of particles of suspension is large enough to be visible from naked eyes. They are greater than 1 nanometre (10^(-9) metre).
4.Suspension shows Tyndall effect because of their large size of particles.
5.When suspension is left for some time, particles get settled in bottom.
6.Therefore, suspension is not stable.
7.The particles of suspension can be separated through the process of filtration.
8.Suspension does not scatter light when particles are settled because in this case suspension breaks.
9.Milk of magnesia, fog, mixture of chalk and water, etc. are some examples of suspension.

Colloidal Solution
Colloidal solution is a heterogeneous mixture of two or more substances. Colloidal solutions appear homogenous because of relatively small size of particles in comparison with suspension. Particles of colloidal solution are called colloid. Colloids are dispersed throughout the solvent. Particles of colloidal solution are not visible through naked eye but scatter the ray of light, i.e. show Tyndall effect. Colloids cannot be separated by filtration but can be separated using centrifugation. Milk, ink, blood, solution of soap or detergent, etc. are some common examples of colloidal solution.

General Characteristics of Colloidal Solution:
1.Colloidal solutions are heterogeneous mixture of two or more substances.
2.Colloidal solutions appear homogeneous.
3.The size of colloids is between the size of particles of solution and suspension, i.e. between 1 nanometer to 1000 nanometer.
4.Colloids cannot be seen even using optical microscope.
5.Colloids show Tyndall effect, i.e. they scatter the ray of visible light.
6.Colloidal solutions may be opaque, translucent or of light colour.
7.Colloids cannot be separated by filtration. But they can be separated by centrifugation. For example fat can be separated by centrifugation from milk.
8.Colloidal solutions are stable since colloids cannot settle down when left undisturbed.

Components of Colloidal Solution:
There are two components of a colloidal solution – dispersed phase and dispersing medium. The solute like component of colloidal solution is called dispersed phase and solvent like component is called dispersing medium. The dispersed phase and dispersing medium may be solid, liquid or gas.

Types of Colloidal Solution:

Colloids are classified on the basis of their components, i.e. dispersed phase and dispersing medium.
1.Liquid Aerosol
2.Solid Aerosol
3.Foam
4.Emulsion
5.Sol
6.Solid foam
7.Gel
8.Solid sol

Gas as dispersing medium:
Aerosol – When particles of solid or liquid dispersed in gaseous medium, the mixture is known as Aerosol. For example – cloud, smog, smoke etc.

Aerosol is of two types – Liquid Aerosol and Solid Aerosol.

Liquid Aerosol – When liquid particles are dispersed phase and gas is dispersing phase, the mixture is known as Liquid Aerosol. For example – fog, mist, hair spray, etc.

Solid Aerosol – When solid particles are dispersed phase and gas is dispersing phase, the mixture is known as Solid Aerosol. For example, smoke, air particulates, automobile exhaust, etc.

Liquid as dispersing medium:

Foam – Mixtures are called foam when liquid is present as dispersing medium and gas is dispersed medium. For example – shaving cream, soap bubbles, etc.

Emulsion – Colloidal solution is called emulsion, when dispersing medium and dispersed phase both are liquid. For example – milk, butter, face cream, etc.

Sol – Colloidal solution is called sol when liquid is dispersing medium and solid is dispersed phase. For example – blood, ink, paint, etc.

Solid as dispersing medium

Solid foam – Solid foam is formed by the mixing of solid as dispersing medium and gas as dispersed phase. For example – Styrofoam, pumice stone, bread, etc.

Gel – Gel is formed by the mixing of solid as dispersing medium and liquid as dispersed phase. For example – gelatin, jelly, hair gel, etc.

Solid sol – Solid sol is formed by the mixing of solid as dispersing medium and solid as dispersed phase. For example - coloured gem stone, cranberry glass, etc.

Separation of Components of Mixture

Centrifugation –
In the method of centrifugation, the centripetal and centrifugal forces are used to separate lighter and heavier components of mixture of two immiscible liquids. This process is used to separate very small solids particles from a liquid mixture.

Example – Milk is the mixture of fat, water, and other constituents. Using the method of centrifugation, most of the fat can be separated from milk. In milk, fat is suspended throughout the milk which is separated out using the method of centrifugation.
When milk is churned rapidly, water which is heavier than fat, migrates away from the centre of centrifuge while fat is forced towards the bottom, which is drained out.

Application of centrifugation –
In pathological test of blood and urine.
In separation of fat from milk.
In washing machines to squeeze the water from wet clothes.

Decantation –
Decantation is used to separate the components from a mixture of two immiscible liquids, such as mixture of oil and water. In a mixture of two immiscible liquids, lighter one and heavier one form separate layer. The lighter one can be decanted after settling of mixture, carefully in other container.
In the process of decantation some of the heavier liquid also poured out with lighter one. Therefore, components from a mixture of two immiscible liquids; can be separated more easily and accurately using a separating funnel.
A separating funnel is usually made of glass with a stop cork with drain pipe at bottom. The heavier liquid which is settled at bottom is drained out from the mixture of two immiscible liquids by opening of stop cork from a separating funnel.

Sublimation
There are many substances which are converted into gas from solid when heated, and converted from gas to solid when cooled without converting into liquid. Such substances are known as sublime. For example – ammonium chloride, naphthalene balls, camphor, etc. Therefore, mixture of one sublime and other substance can be separated using the method of sublimation.
The mixture of ammonium chloride and common salt can be separated out using the process of sublimation. For this, the mixture is heated in a China dish. The China dish is covered by an inverted funnel. Cotton is used for plugging the opening of the funnel. After heating, ammonium chloride is converted into vapour and gets deposited over the inner surface of funnel; due to cooling. This leaves the common salt in China dish. Ammonium chloride can be taken out by scratching from the inner wall of funnel.

Chromatography –
Chromatography is a method of separation which works on the principle of travel speed of components of a mixture. This method is used for separating dyes and pigments from a mixture. Ink is the mixture of dyes of different colours.
There are many types of chromatography. The dyes from an ink can be separated using paper chromatography.
For this, a strip of filter paper is dipped in the ink. Particles of dye start rising on filter paper; along with water. Different dyes rise with different speed because of different types of solubility in water and go up to certain heights.

Application of chromatography -
1.In the separation of colours from a dyes.
2.In the separation of pigments from natural colours.
3.In the separation of drugs from blood for pathological tests.

Distillation –
The process of distillation is used to separate two miscible liquids. The technique of distillation is based on the difference in boiling points of components of mixture of miscible liquids. Distillation is to separate the liquids which do not decompose even upto their boiling points and should boil at more than 250C.
In the process of distillation, the mixture is heated after keeping in a retort or distillation flask. The liquid which boils at lower temperature is vaporized at lower temperature. The vapour so obtained is passed through a tube and gets condensed in a separate container; leaving liquid with higher boiling point in the retort or distillation flask.
Distillation is used to separate the components of the mixture of two miscible liquids that boils without decomposition and have sufficient difference in their boiling points.
The process of distillation is used to purify many liquids, such as water.

Fractional Distillation
Fractional distillation is the process of separation of components of mixture into parts or fraction on the basis of fractional differences in their boiling points.
Fractional distillation is done when the difference in boiling points of the components of miscible liquids is less than 250C. In the process of fractional distillation, a fractional column is used along with retort or distillation flask.
Fractional column is a tube which contains glass beads, which facilitate surface for the vapour to cool and condense repeatedly.

Example – Ethanol and water are separated from their mixture using fractional distillation. The boiling point of water is 100⁰C while the boiling point of ethanol is 78.4⁰C. Since the difference of their boiling point is less than 25⁰C, thus they are separated using fractional distillation.

Some of the Applications of Fractional Distillation:
1.In petroleum refineries, petrochemical and chemical plants, natural gas processing and cryogenic air separation plants.
2.In oil refineries to separate crude oil into useful substances (or fractions).
3.In the process of organic juice.
4.In the separation of oxygen, liquid nitrogen and argon from air.

Separation of different gases from air –
Air comprises of nitrogen, oxygen, carbon dioxide and argon as major components. Since air is the cheapest source of these gases, thus these are extracted from air at large scale
After liquefaction of air by repeated compression and cooling; nitrogen, oxygen, carbon dioxide and argon are extracted using fractional distillation.
Liquid nitrogen has boiling point equal to - 190⁰C and thus turns into gas first and separated from air.
The boiling point of argon is - 186⁰C, therefore it is extracted after argon.
The boiling point of oxygen is - 183⁰C, thus it is collected after the extraction of argon.
Carbon dioxide turns into solid at a temperature of - 97⁰C, therefore, it is removed while air is put under liquefaction.

Use –
1.Nitrogen is used as fertilizers, oxygen is used in hospitals and argon is used in bulbs.

Physical and Chemical Changes

Physical Change: The change in which no new substance is formed is called a physical change. During a physical change, chemical properties do not change but physical properties do change.

Chemical Change: The change in which a new substance is formed is called a chemical change. During a chemical change, chemical properties change.

Pure Substances

Elements and Compounds are considered as pure substances.
Elements – Substances that is made of only one element are called elements, such as hydrogen, carbon, oxygen, silver, gold, etc
.
Compounds – Substances that is made of one or more elements by chemical combination are called compounds, such as water, carbon dioxide, copper oxide, hydrochloric acid, etc.
A compound does not contain the properties of its constituent elements and shows quite different characteristics.

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