IS MATTER AROUND US PURE

IMPORTANT TERMS

Matter                         Anything which has a mass and occupies space is called matter.

Pure substance            A pure substance is a material that has constant composition and has consistent properties throughout the sample.

Element                       An element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.

Compound                   It is a substance that results from a combination of two or more different chemical elements.

Physical change           It is any change in matter that involves the substance going from one physical state to another without any change in its chemical composition.

Chemical change          Chemical changes involve chemical reactions and the formation of new products.

Mixture                        It is a material made up of two or more different substances which are mixed but are not combined chemically.

Solution                       It is a homogeneous mixture of two or more substances.

Suspension                  A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.

Colloid                         A heterogeneous mixture that has relatively smaller size of particles, as compared to that of a suspension, so the mixture appears to be homogeneous.

Matter

On the basis of the physical state, matter is classified into three main types: solids, liquids and gases. The other two types in the extended classification include plasma and Bose-Einstein condensates. On the basis of chemical composition, matter is classified into two main types: pure substances and mixtures.

Pure Substance

It is a substance which consists of a single type of substance. It has constant composition and has consistent properties throughout the sample. E.g.:- Hydrogen, Oxygen, Water, Sugar, Iron, Common salt etc. There are two types of pure substance: Element and Compound.

Element

• Robert Boyle was the first scientist to use the term element in 1661.
• Antoine Laurent Lavoisier (1743-94) defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
• Elements are of three types: Metals, Non- metals and Metalloids.

 

Metal

Metals usually show some or all of these properties: They have lustre (shine). They are malleable and ductile. They are good conductors of heat and electricity. They are sonorous. E.g.:- iron, aluminium, zinc, mercury, copper, silver, gold etc.

Non-metal

Non-metals usually show some or all of these properties: They do not have lustre. They are not malleable or ductile. They are poor conductors of heat and electricity. They are not sonorous. They display a variety of colours. E.g.:- hydrogen, oxygen, nitrogen, iodine, carbon, sulphur etc.

Metalloids

Metalloids are elements which show some properties of metals and some properties of non-metals. E.g.:- boron, silicon, germanium etc.

Compound

A compound is a substance formed when two or more elements are chemically bonded together. The property of compound has always different from its constituents.  It has a fixed composition.  The constituents of compound can be separated by chemical or electrochemical reactions. E.g.:- Water (H2O), Common Salt (NaCl), Sugar (C6H12O6) etc.

 

Mixtures

It is a substance which consists of two or more pure substances. It has a variable composition. It shows the properties of the constituent substances. Its constituents can be separated by physical methods. E.g.:- sea water, minerals, soil, air, sand and salt, sugar in water, salt in water etc. Mixtures are of two types. They are homogeneous mixture and heterogeneous mixture.

Homogeneous mixture

It is a mixture which has a uniform composition. The particles of the mixture are not visible by the naked eye. The particles cannot be separated by filtration. The mixture is stable (the particles do not settle down). The path of a beam of light is not visible in the mixture.

Heterogeneous mixture 

It is a mixture which has a non -uniform composition. The components of a heterogeneous mixture can be separated by simple methods like hand picking, sieving, filtration etc.

 

Solution

A solution has a solvent and solute as its components. The component in the larger amount is the solvent and the component in the lesser amount is the solute.  E.g.:- solution of salt in water, solution of sugar in water, iodine in water (tincture iodine), soda water etc.

• Saturated solution: It is a solution which cannot dissolve any more of a solute at a given temperature.
• Solubility: It is the amount of solute present in a saturated solution of the substance. The solubility of different substances is different. The solubility of substances varies with temperature.
• Unsaturated solution: It is a solution which can dissolve some more of the solute at a given temperature.

 Properties of solutions

• True solution is a homogeneous mixture.
• The particles are cannot be seen by the naked eye.
• The solute particles cannot be separated by filtration.
• The solute particles do not settle down and the solution is stable.
• The particles do not scatter a beam of light passing through it and the path of light is not visible in the solution.

 The concentration of a solution

The concentration of a solution is the amount of solute present in a given amount of the solvent or solution. Concentration of a solution = Amount of solute/ Amount of solvent Or, Concentration of a solution = Amount of solute/ Amount of solution.

There are several ways of expressing the concentration of a solution like “mass by mass percentage” or as “mass by volume percentage”.

Mass by mass percentage of a solution = (Amount of solute/ Mass of solution) X 100

Mass by volume percentage of a solution = (Amount of solute/ Volume of solution) X 100                                                                          

 

Suspension

A suspension is a heterogeneous mixture of two or more substances. E.g.:- solution of sand in water, solution of chalk powder in water etc.

Properties of suspension

• 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, which means that a suspension is unstable.
• They can be separated from the mixture by the process of filtration.

Colloid

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.

 

Properties of colloid

• A colloidal solution is a heterogeneous mixture of two or more substances. E.g.:- mixture of starch in water, mixture of egg albumin in water, milk, air containing dust and smoke etc.
• Colloidal solution is a heterogeneous mixture.
• The particles cannot be seen by the naked eye.
• The solute particles cannot be separated by filtration.
• The solute particles do not settle down and the solution is stable.
• The particles scatter a beam of light passing through it and the path of light is visible in the solution.

 

Tyndall effect

• The scattering of a beam of light by particles of heterogeneous mixture is called the Tyndall effect after the name of the scientist who discovered this effect.

• Tyndall effect can be seen when light enters a room through a small hole due to scattering of light by the dust and smoke particles.
• Tyndall effect can be seen in a dense forest due to scattering of light by water droplets in the mist.

 

Techniques Used to Separate the Components of Mixtures

Evaporation

This method is used for separating a volatile component (solvent) from a non-volatile component (solute) by heating the mixture. E.g., separation of salt and water, sugar and water, dye from ink etc.

Centrifugation

It is used to separate denser particles and lighter particles from a mixture by using a centrifuging machine. The principle is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly. It is used in diagnostic laboratories for blood and urine tests, in dairies and home to separate butter from cream, in washing machines to squeeze out water from wet clothes.

Decantation (Using separating funnel) 

This method is used for separating a mixture of immiscible liquids. Liquids separate into different layers depending on their densities. It is used to separate mixture of oil and water, in the extraction of iron from its ore etc.

Sublimation

This method is used to separate a mixture of a sublimable component from a non sublimable component by heating the mixture. It is used to separate mixture of salt and ammonium chloride (sublimable component).

Chromatography

Chromatography is a technique used for separation of those solutes that dissolve in the same solvent.  It is used to separate colours in a dye, pigments from natural colours, drugs from blood etc.

Crystallisation

It is a process that separates a pure solid in the form of its crystals from a solution and this method is used to purify solids. It is used in the purification of salt that we get from sea water, separation of crystals of alum (phitkari) from impure samples, pure copper sulphate from an impure sample etc.

Crystallisation technique is better than simple evaporation technique because:

1. Some solids decompose or some, like sugar, may get charred on heating to dryness.
2. Some impurities may remain dissolved in the solution even after filtration, which may contaminate the solid on evaporation.

Distillation

This method 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. e.g., separation of a mixture of acetone and water.

Fractional distillation

It is used to separate a mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K. Fractional distillation process is used for the separation of different gases from air, different factions from petroleum products etc.

Physical and Chemical Changes

A physical change brings changes in the physical properties (like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc.) of the matter. It may or may not be reversible.

Chemical change brings change in the chemical properties of matter and formation of a new substance always takes place. A chemical change is also called a chemical reaction.

Burning of a candle is an example of both physical and chemical changes. Melting and evaporation of wax are the physical changes and burning of the wax is a chemical change.

INTERESTING FACTS

• Mercury is the only metal that is liquid at room temperature.
• A solution of iodine in alcohol known as ‘tincture of iodine’, has iodine (solid) as the solute and alcohol (liquid) as the solvent.
• Air is a homogeneous mixture of a number of gases. Its two main constituents are: oxygen (21%) and nitrogen (78%).
• Examples of solids which sublime are ammonium chloride, camphor, naphthalene and anthracene.
• Graphite is the only non-metal that is good conductor of electricity.
• Ninety two elements are naturally occurring and rest are man-made.
• Alloy is a homogeneous mixture of metals and it is considered as a solid solution.