Chapter 2 – Is Matter Around Us Pure?

Topics

• 1. Introduction
• 2. What is Matter?
• 3. Elements
• 4. Mixtures
• 5. Compounds
• 6. Solutions
• 7. Types of Solutions
• 8. Suspensions
• 9. Colloids
• 10. Concentration of a Solution
• 11. Separation of Mixtures
• 12. Separation of Mixture of two Solids
• 13. Separation of Mixture of a Solid and a Liquid
• 14. Separation of Mixture of Two (or More) Liquids
• 15. Physical and Chemical Changes

Introduction

• Everything around us is made up of matter.
• For example: – Wood, paper, even human beings are made up of matter.
• All the matter present around us is not pure. It can be pure or impure.
• We will try to learn whether matter around is pure or not. And what all techniques we can use to get a pure substance.

What is Matter?

• Matter is anything that has mass and occupies space. It can be a solid, liquid or gas.
• For Example: – Sun, Clouds, Wood, human beings, Juice, Chalk, Salt, Clothes etc. all are made up of matter.

• Matter exists in two forms pure or impure

• Matter can be categorized as 2 types:-

1. Pure Substance
   1. A pure substance is one which is made up of only one kind of atoms or molecules.
   2. For Example: – Sulphur element is made up of only one kind of particles called Sulphur atoms.
2. Impure Substance
   1. A mixture is one which contains two or more different kinds of particles (atoms or molecules).
   2. Or a mixture contains one or more pure substances mixed together.
   3. For Example: – A salt solution: – It is a mixture of two pure substances: – salt and water.
   4. Note: – All mixtures are impure substances because they contain more than one kind of particles.
   5. Mixtures can be of two types: – Homogeneous and Heterogeneous.

Elements

• An element is a substance which cannot be spilt up into two or simpler substances by the means of chemical methods of applying heat, light or electric energy.
  • For Example: – Hydrogen is an element which cannot be split into two or more simpler substances.
• An element cannot be split into two (or more) simpler substances because it is made up of only one kind of atom.
• Therefore, Element can also be defined as: – An substance which is made up of only one kind of atoms.
• For Example: – Copper metal is made up of only one kind of atoms called “copper atoms”.
• There are 118 elements known till now, out of which 94 elements occur in nature while remaining 24 are prepared artificially.
• Examples: – Helium, Carbon, Helium etc.
• Elements can be solids, gases or liquids.
• In this world all the materials are made up of one or more elements even our human body is made up of combination of certain elements.

Gold Bar consists of Gold elements

• Note:- All the elements can be divided into 3 groups:-

1. Metals
2. A metal is an element that is malleable, ductile and conducts electricity.
3. For example: – Iron, copper, Zinc etc.

1. Non-Metals
2. A non-metal is an element that is neither malleable nor ductile and does not conduct electricity.
3. For Example: – Carbon, Sulphur, Phosphorous etc.

3. Metalloids
4. The elements that show some properties of metals and some properties of non-metals are called metalloids.
5. For Example: – Boron, Silicon etc.

Mixtures

• A mixture is a substance which consists of two or more elements or compounds not chemically combined together.
• For Example: – Air is a mixture of gases like oxygen, nitrogen, argon, CO₂and water vapour.
• All solutions are mixtures.
  • For-Example: – salt-solution (also known as brine) is a mixture of sodium chloride in water.
• Types of Mixtures

1. Homogeneous Mixture
   1. Those mixtures, in which the substances are completely mixed together and are indistinguishable from one another, are called homogeneous mixtures.
   2. For example: – All homogeneous mixtures are solutions. Example: – Soda water, Soft drinks, lemonade etc.
   3. A Mixture of sugar in water (called sugar solution).

Lemonade

2. Heterogeneous Mixture
   1. Those mixtures in which the substances remain separate and one substance is spread throughout the other substance as small particles, droplets or bubbles are called heterogeneous mixtures.
   2. The suspensions of solids in liquids are also heterogeneous mixtures.
   3. A mixture containing two (or more).
   4. All the suspensions and colloids are heterogeneous mixtures.
   5. For Example: – Sugar and sand mixture, muddy river water, soap solution.

Mixture of Oil and water

Compounds

• A compound is a substance made up of two or more elements chemically combined in a fixed proportion by mass.
• For example: – H₂O is a compound made up of two elements hydrogen and oxygen, chemically combined in a fixed proportion (1:8) by mass.
• Note: – Compounds can be further divided into 3 classes: acids, bases and salts.

Salt

Solutions

• A solution is a homogeneous mixture of two (or more substances).
• A homogeneous mixture means that the mixture is just the same throughout.
• For examples: – Salt solutions, Sugar solutions, Air, Soda water etc.
• Only soluble substances form true

Properties of Solutions

1. A solution is a homogeneous mixture.
2. The particles of a solution are smaller than 1 nm (10^-9metre) in diameter. So, they cannot be seen by naked eyes.
3. Because of very small particle size, they do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution.
4. The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed, that is, a solution is stable.
5. A true solution does not scatter light.

Important Note:-

• A solution has a solvent and a solute as its components.
• The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent.
• The substance which is dissolved in a liquid to make a solution is called solute.

Types of Solutions

• The various types of solutions are:-

1. Solution of solid in a solid: – Metal alloys are the solutions of solids in solids.
   • For example: – Brass is a solution of zinc in copper.
2. Solution of solid in a liquid: – This is the most common type of solution.
   • For example: – A solution of iodine in alcohol called “tincture of iodine”.
3. Solution of liquid in a liquid: – Vinegar is a solution of acetic acid in water.
4. Solution of Gas in a liquid: – Soda-Water is a solution of carbon dioxide gas in water.
5. Solution of Gas in a Gas: – Air is a solution of gases like oxygen, argon, carbon dioxide and water vapour etc. in nitrogen gas.

Suspensions

• Those substances which are insoluble in water form suspensions.
• A suspension is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving.
• For Example:-Chalk-powder, muddy water, milk of magnesia, flour in water etc.
• If a beam of light is passed through a chalk and water suspension, it scatters the beam of light and renders its path visible inside it.

Colloids

• A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions.
• For Example: – Soap solution, Milk, Ink, Blood and solutions of synthetic detergents.

• In a true solution, the solute particles are so small that they cannot scatter or reflect light rays falling on them.
• In a colloidal solution (or colloid), the particles are big enough to scatter light.
  • If a beam of light is put on a colloidal solution kept in a beaker in a dark room, the path of light beam is illuminated and becomes visible when seen from the side.
  • The path of light beam becomes visible because colloidal particles are big enough to scatter light falling on them in all directions.
• The scattering of light by colloidal particles is known as Tyndall effect.
• Tyndall effect can also be observed when a fine beam of light enters a room through a small hole. This happens due to the scattering of light by the particles of dust and smoke in the air.

  (a) Solution of copper sulphate does not show Tyndall effect,

     (b) Mixture of water and milk shows Tyndall effect.

• Tyndall effect can be observed when sunlight passes through the canopy of a dense forest. In the forest, mist contains tiny droplets of water, which act as particles of colloid dispersed in air.

• Note: –
• A true solution can be distinguished from a colloidal solution by the fact that a true solution does not scatter a beam of light passing through it but a colloidal solution scatters a beam of light passing through it and renders its path visible.
• Colloids are heterogeneous in nature, though they appear to be homogeneous.

Properties of Colloids

1. A colloid appears to be homogeneous but it is actually it is heterogeneous.
2. The size of the particles in a colloid is bigger than those in a true solution but smaller than those in a suspension. It is between 1 nm and 100nm in diameter.
3. The particles of most of the colloids cannot be seen even with microscope.
4. It scatters a beam of light passing through it.

• Note:-There is a special technique known as centrifugation can be used to separate the colloidal particles from a colloidal solution.
• The components of a colloidal solution are the dispersed phase and the dispersion medium.
• The solute-like component or the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium.
• Colloids are classified according to the state (solid, liquid or gas) of the dispersing medium and the dispersed phase.

Dispersed Phase	Dispersing Medium	Type	Example
Liquid	Gas	Aerosol	Fog, clouds, mist
Solid	Gas	Aerosol	Smoke
Gas	Liquid	Foam	Shaving Cream
Liquid	Liquid	Emulsion	Milk, Face cream
Solid	Liquid	Sol	Milk of  Magnesia, mud
Gas	Solid	Foam	Foam, Rubber, Sponge,Pumice
Liquid	Solid	Gel	Jelly, Cheese, Butter
Solid	Solid	Solid Sol	Coloured gemstone,Milky Glass

Concentration of a Solution

• At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving is said to be a saturated solution.
  • In other words, when no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.
• If a saturated solution at a particular temperature is heated to a higher temperature, then it becomes unsaturated.
• The amount of the solute present in the saturated solution at this temperature is called its
• If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution.
• The concentration of a solution is the amount of solute present in a given quantity of the solution.
• The amount of solute dissolved in a given mass or volume of solvent.
  • Concentration of solution = (Amount of solute)/ (Amount of solution)

Or (Amount of solute)/ (Amount of solvent)

Problem 1:-

A solution contains 40 g of common salt in 320 g of water. Calculate the concentration in terms of mass by mass percentage of the solution

Answer 1:-

Mass of solute (salt) = 40 g

Mass of solvent (water) = 320 g

Also, Mass of solution = Mass of solute + Mass of solvent

= (40 g + 320 g)

= 360 g

Mass percentage of solution

= [(Mass of solute)/ (Mass of solution)] ×100

= (40/360) ×100 =11.1%

Solubility

• The maximum amount of a solute which can be dissolved in 100gms of a solvent at a specified temperature is known as solubility of that solute in that solvent (at that temperature).

Separation of Mixtures

• The method to be used for separating a mixture depends on the nature of its constituents.
• The various physical processes which are commonly used to separate the constituents of mixtures are:-

1. Sublimation
2. Filtration
3. Centrifugation
4. Evaporation
5. Crystallization
6. Chromatography
7. Distillation
8. Fractional distillation
9. Separating Funnel

Separation of Mixture of two Solids

• Following are the methods used to separate two solid substances

1. By using a suitable solvent
2. By the process of sublimation
3. By using a magnet

1. By using a suitable solvent

• A mixture of sugar and sand can be separated by using water as a solvent.
• Sugar is soluble in water whereas sand is insoluble in water. This difference in the solubilities of sugar and sand in water is used to separate them.

1. Separation by Sublimation

• The changing of a solid directly into vapours on heating, and of vapours into solid on cooling is called as sublimation.
• The solid which undergoes sublimation is called as “sublime”.
• The process of sublimation is used to separate those substances from a mixture which sublime on heating.
• The solid substance obtained by cooling the vapours is known as “sublimate”.
• For example: – Ammonium chloride, iodine, camphor, naphthalene etc. sublime on heating and can be recovered in the form of a sublimate by cooling into vapours.
• Most of the substances do not undergo sublimation.

Separation of ammonium chloride and salt by sublimation.

1. Separation by Magnet

• If a mixture contains iron as one of the constituents, it can be separated by using a magnet.
• For Example: – A mixture of iron fillings and sulphur powder can be separated by using a magnet. The iron fillings will get attracted to the magnet and sulphur won’t.

Separation of Mixture of a Solid and a Liquid

• All the mixtures containing a solid and a liquid are separated by the one of the following processes:-

1. By filtration
2. By centrifugation
3. By evaporation
4. By crystallization
5. By chromatography
6. By distillation
7. By Filtration
   1. Filter paper is a round piece of special paper which has millions of pores in it.
   2. The liquids can pass through the tiny pores of a filter paper but solid particles are left behind.
   3. The solid which remains behind on the filter paper is called residue.
   4. The liquid which passes through the filter paper is called filtrate.
   5. A mixture of sand and water can be separated by filtration.
   6. Filtration cannot remove any solid substances which are dissolved in a liquid.

1. By Centrifugation

• Centrifugation is a method for separating the suspended particles of a substance from a liquid in which the mixture is rotated at a high speed in a centrifuge.
• The mixture of fine suspended particles in a liquid is taken in a test-tube. This tube is placed in centrifuge machine and rotated rapidly for some time.
• As the mixture rotates round rapidly, a force acts on the heavier suspended particles in it and brings them down to the bottom of the test-tube.
• The clear liquid, being lighter remains on the top.
• Separating cream from milk:-
  • The process of centrifugation is used in diaries to separate cream from milk.
  • The milk is put in a closed container in big centrifuge machine.
  • When the machine is switched “on”, the milk is rotated at a very speed in its container. As a result milk separates into “cream” and skimmed milk.
  • The cream being lighter floats over the skimmed milk.

3. By Evaporation

• The changing of liquid into vapours (or gas) is called evaporation.
• This process is used to separate a solid substance that has dissolved in water (or any other liquid).
• The use of this process for separating a mixture is based on the fact that the liquids vaporise easily whereas solids do not vaporise easily.
• For Example: – The common salt dissolved in water can be separated by the process of evaporation.
• This process is used to on a large scale to obtain common salt from sea-water.
• Evaporation is also used in recovering dissolved solid substances from liquid mixtures (or solutions) but the liquid itself cannot be recovered by this method. The liquid vaporises and gets lost to the air.

Getting salt from sea water by the process of evaporation.

4. By Crystallisation

• The process of cooling a hot, concentrated solution of a substance to obtain crystals is called crystallization.
• 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.
• Following are the steps involved in obtaining pure solid substance from impure sample:-

1. The impure solid substance is dissolved in the minimum amount of water to form a solution.
2. The solution is filtered to remove insoluble impurities.
3. The clear solution is heated gently on a water bath till a concentrated solution or saturated solution is obtained.
4. Allow the hot, saturated solution to cool slowly.
5. Crystals of pure solid are formed. Impurities remain dissolved in solution.
6. Separate the crystals of pure solid by filtration and dry.
7. For Example: –
   1. Impure copper sulphate can be purified by the method of crystallisation.

5. Separation by Chromatography

• Chromatography is a technique of separating two or more dissolved solids which are present in a solution in very small quantities.
• This separation is based on the fact that though two or more substances are soluble in the same solvent but their solubilities may be different.
• A special type of paper called “chromatography paper” is used for carrying out separations by chromatography.
• Black ink is a mixture of several coloured substances which can be prepared by paper chromatography.
• Applications of chromatography:-

1. It is used to separate solutions of coloured substances.
2. Used in forensic science to detect and identify trace amounts of substances (like poisons) in the contents of bladder or stomach.
3. Also used to separate small amounts of products of chemical reactions.

Separation of dyes in black ink using chromatography

6. Separation by Distillation

• The process of distillation is used to get both salt as well as water from salt-water mixture.
• It is process of heating a liquid to form vapour, and then cooling the vapour to get back liquid.
• Liquid <-> Vapour (or Gas)

         (Heating/Cooling)

• The liquid obtained by condensing the vapour is called “distillate”.
• When a homogeneous mixture of solid and a liquid is heated in a closed distillation flask, the liquid, being volatile, forms vapour.
• The vapours of liquid are passed through a “condenser” or “Liebig condenser” where they get cooled and condense to form pure liquid.
• This pure liquid is collected in a separate vessel.
• The solid, being non-volatile, remains behind in the distillation flask.

Separation of two miscible liquids by distillation

Separation of Mixture of Two (or More) Liquids

• Following are the 2 methods used to separate all the mixtures containing liquids:-
  • By the process of fractional distillation
  • By using a separating funnel

1. By the process of fractional distillation

• Fractional distillation is a process of separating two (or more) miscible liquids by distillation, the distillate being collected in fractions boiling at different temperatures.
• The more volatile liquid (having lower boiling point) distils over first, and the less volatile liquid (having higher boiling point) distils over later.
• A simple fractionating column is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly.
• For example: – Mixture of acetone and water can be separated by fractional distillation.
• Applications of Fractional Distillation

1. Fractional distillation is used to separate mixtures of miscible liquids.
2. It is used to separate crude oil “petroleum” into useful fractions such as kerosene, petrol or diesel etc.
3. It is used to separate gases of the air.

Fractional distillation

2. Separation by Separating Funnel

• A mixture of two immiscible liquids can be separated by using separating funnel.
• The separation of two immiscible liquids by a separating funnel depends on the difference in their densities.
• The denser liquid forms the lower layer whereas the lighter liquid forms the upper layer.
• For Example: – Water and Kerosene can be separated by using this method. Water being heavier forms the lower layer in the funnel whereas kerosene being lighter forms an upper layer.

Separation of immiscible liquids

Physical and Chemical Changes

• Changes in energy are always accompanied by a particular chemical or physical change.

Physical Changes

1. The changes in which no new substance is formed are called physical changes.
2. The molecular composition remains totally the same.
3. For example, the molecular composition of ice and water is not changed.
4. The energy needed to bring a physical change is equal to the amount of energy required to reverse the change. There is no change in energy.
5. The changes are reversible and temporary. The reaction gets reversed if the cause producing the change is removed. For example, water on freezing forms ice and ice on melting forms water.
6. Examples of physical change
   1. Dissolution of sugar in water
   2. Melting of ice
   3. Freezing of water
   4. Boiling of water
   5. Melting of wax

Chemical Changes

• The change in which the molecular composition is completely changed and a new product is formed is called a chemical change. A new product is formed.
• The changes in Chemical change are irreversible and permanent. A chemical change cannot be reversed by changing or altering the experimental changes.
• During a chemical change, the energy changes occur. There is an energy difference in the breaking of old bonds in reactants and the formation of new bonds in products.
• Examples of Chemical Change
  • Burning of wood or paper
  • Burning of camphor
  • Souring of milk
  • Burning of candle
  • Digestion of food