Is Matter Around Us Pure Class 9 Short Notes | Chapter 2
Introduction
Anything which occupies space and has mass is called matter. Matter can be divided in two categories
- Pure Substance
- Impure Substances (Mixtures)
Pure Substance
Pure substances means that all elements have same chemical properties. A pure substance is made up of same kind of elements.
Pure
‘Pure’ word means that there is no mixing in a substance. But according to scientific language all things are mixture of so many substances, not of single one. That’s why they are not pure. E.g. Milk, water, fat, etc.
Substance
A substance is a kind of matter that cannot be separated into other kind of matter by any physical process. A pure substance is made up of same kind of elements.
Compound
A Substance made from two or more different elements that have been chemically joined. Example-Water (H2O) which is made from the elements hydrogen and oxygen
Difference between Mixtures and Compounds
| Compunds | Mixtures |
|---|---|
| The composition of elements in a compound is fixed | the composition of elements present in a mixture is not fixed |
| the properties of a compund are different from those of its elements. | it shows the properties of all its constituent elements |
| its constituents can be separated by chemical methods only | its constitument can be separated by physical methods |
| A compound is always homogeneous in nature | the mixtures can be homogeneous or heterogeneous |
Mixture
It is a substance in which two or more substances (element or compound) are simply mixed together in any proportion.
Examples of Common Mixtures are as Follows:
- Seawater - It is a mixture of various salts and mixture.
- Gunpowder – It is a mixture of Potassium Nitrate and carbon.
- Ink – It is a mixture of different coloured dyes which can be separated by using Chromatography.
- Crude oil – It is a mixture of organic compounds that includes hydrocarbons.
- Dry Air – It is a type of much different type of gases like nitrogen, oxygen, carbon dioxide, argon, neon, and other tiny traces gases. (Air generally contains water vapour as a part of mixture.
Types of Mixture
Mixture is of two types :
Homogenous mixture
Heterogenous mixture
Homogenous Mixture
These types of mixtures have no visible boundaries of separation between the various constituents.
Example :- Sugar in water. It has a uniform composition throughout its mass.
Heterogenous Mixture
These types of mixtures have visible boundaries of separation between the various constituents.
Example :- Mixture of sugar and sand. It does not have a uniform composition throughout its mass.
Differences between Homogeneous and Heterogeneous
| Homogenous Mixtures | Heterogeneous Mixtures |
|---|---|
| They have a uniform composition throughout | They have a non-uniform composition |
| We cannot separate the components of the mixture through physical processes | We can separate the components through physical processes |
| Components cannot be seen through naked eyes | Components can easily be seen through naked eyes |
| The mixture is in single phase throughout | The substances can be of two different phases and we may see separate layers of the substances |
| Example :- A mixture of water and milk | Example :- A mixture of oil in water |
Elements
An element is a substance that cannot be further broken down into a simpler substance by using common chemical methods. All matter is fundamentally composed of elements. More than 119 elements have been discovered and many more are in the process of being discovered. Every element has a fixed place in the periodic table, depending on its properties.
Metals
Metals are the materials possessing or holding the characteristics of being hard, fusible, shiny, malleable, ductile, and so on. Examples of metals (materials) are Silver, Gold, Copper, Aluminium, Iron, and many more.
Nonmetals
Non-metals do not hold the characteristics of metals; it means they are not hard, shiny, fusible, malleable, ductile, and so on. Many materials like Sulphur, coal are too soft and dull in appearance. They can be broken down into very fine thin powdery mass when tapped with a hammer. They are neither sonorous nor very poor conductors of heat and electricity. Non-metal examples are oxygen, carbon, Sulphur, and more.
Metalloids
Metalloids are the elements which are having a combination of some properties of metals along with some properties of nonmetals. Their properties are intermediate between the properties of metals and nonmetals, they are also called semi-metals.
Example: – Boron, Silicon, Germanium, etc
Solution
A solution is a homogenous mixture of two or more substances. E.g., Nimboo pani, soda water.
A solution has a solvent and a solute as its components.
Solvent
The component of the solution that dissolves the other component in it is called the solvent.
Solute
The component of the solution that is dissolved in the solvent is called the solute.
Properties of a Solution
A solution is a homogenous mixture.
We cannot see the particles of a solution through naked eyes as they as are small as 1 nanometer in diameter.
The path of light is not visible through the solution. The particles of a solution do not scatter light through them as they are extremely small.
We cannot separate the particles of a solution by methods of filtration.
Concentration of a solution
Saturated solution
When no more amount of solute can be dissolved in a solution at a given temperature, it is called a saturated solution.
Unsaturated solution
When more amount of solute can be dissolved in a solution at given temperature, it is called a saturated solution.
Solubility
The amount of the solute present in the saturated solution at the given temperature is called its solubility.
Concentration
Concentration refers to the amount of a substance per defined space or can be defined as the ratio of solute in a solution to either solvent or total solution.
Two methods of finding concentration of solution :-
Mass by mass percentage of a solution = (Mass of solute/Mass of solution) x100
Mass by volume percentage of a solution = (Mass of solute/Volume of solution) x100
Suspension
suspension is formed when two or more substances non-uniform manner. Heterogeneous mixtures are suspensions. The solute does not mix with the solvent and can be viewed through naked eyes.
Properties of Suspensions
- A suspension is a heterogeneous mixture.
- We can see the particles of suspensions through naked eyes.
- We can see the path of light through the particles of a suspension.
- The particles of suspension tend to settle down when left undisturbed. Then, they can be separated using filtration.
Colloidal solutions
A colloidal solution or a colloid is a uniform solution of two or more substances. The particles are relatively very small that the solution appears as a homogeneous mixture but it is not.
Properties of colloids
- Colloids are heterogeneous in nature.
- The particles of a colloid cannot be seen through naked eyes.
- The particles scatter a beam of light passed through a colloid and produce Tyndall effect.
- Colloids are stable in nature. The particles of colloids do not settle down if left uninterrupted.
- We cannot separate the particles of a colloid through filtration. We use a method called Centrifugal to separate the particles of a colloid.
Tyndall Effect
When a beam of light is passed through a colloid the particles of the colloid scatter the beam of light and we can see the path of light in the solution.
For Example :- when a ray of light enters a dark room it is scattered by the dust particles present in the air and we can see the path of light clearly.
Methods of Separation of Mixtures
Evaporation
Basic principal :- Out of the two components of a mixture one can evaporate [i.e., has less boiling point] and other has higher boiling point.
Centrifugal
Basic principle
Separation of Substances or particles on the basis of their density, when mixture is rotated very fast, then denser particles are forced at the bottom and lighter particles stay above.
Applications
Used in diagnostic labs for blood and urine tests.
Used in dairies and home to separate butter from cream.
Used in washing machines dryers to squeeze out water from clothes.
Separating Funnel
Basic principle
Two immiscible liquids (which do not dissolve in each other) can be easily separated by putting in a separating funnel.
Applications
Separation of oil from water.
Extraction of iron from its ore. Lighter slag is removed from above the molten iron.
Sublimation
Basic principle
Out of the two components, one will sublime (directly converts to gas from solid) and other will not.
Applications
Camphor, naphthalene, anthracene, NH,Cl can sublime.
Chromatography
Basic principle
Coloured components of a mixture can be separated by using an Adsorbent on which they are adsorbed at different rates.
Applications
- To separate colours of a dye.
- To separate pigments from natural colours like chlorophyll.
- To separate drugs from blood.
Distillation
Basic principle
Based on Separating mixture of miscible liquids having different boiling points, followed by condensation. Out of the two components one has a lower boiling point and other has higher boiling point. This is used to separate two or more miscible liquids.
Applications
- In petroleum refineries, petrochemical and chemical plants, natural gas processing and cryogenic air separation plants.
- In oil refineries to separate crude oil into useful substances (or fractions).
- In the separation of oxygen, liquid nitrogen and argon from air.
Crystallisation
Basic principle
To remove impurities from a mixture by first dissolving in a suitable solvent and then crystallising out one component.
Applications
Purification of salt from sea water.
Separation of crystals [e.g., alum (phitkari), copper sulphate] from their impure crystals.
Physical vs Chemical Changes
Physical and Chemical changes
Physical changes
The changes in which no new substance are formed,are called physical changes.
In a physical change,the substances involved do not change their identity.They can be easily returned to their original form by some physical changes.
For Ex:Freezing of water,Boiling of water,Condensation of steam,Making a solution,Glowing of electric bulb,stretching of rubber band,cutting or tearing a piece of paper etc.
Chemical Changes
The changes in which new substance are formed,are called chemical changes.
In a chemical change,the substances involved change their identity ie they get converted into entirely new substance.
For Ex:Burning of magnesium ribbon,Rusting of iron,Formation of curd from milk,Cooking of food etc
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