Matter Around Us Online Test 9th Science Lesson 10 Questions in English

Matter is everything around us. The air we breathe, the food we eat, the pen we write, clouds, stones, plants, animals, a drop of water or a grain of sand everything is matter. Samples of any of these materials have two properties in common. They have mass and they occupy space. Not all things that we see or feel are matter. For example, sunlight, sound, force and energy neither occupy space nor have any mass. They are not matter.

Broadly speaking, matter has been classified into pure substances and mixtures. From the point of view of chemistry, pure substances are those which contain only one kind of particles whereas impure substances (mixtures) contain more than one kind of particles. The two types of pure substance are elements and compounds. Two types are impure substance are homogeneous and heterogeneous.

The substance that cannot be broken into simpler substances is called elements. All l substances on earth are made up of certain simple substances called elements. Plants, cats, apples, rocks, cars and even our bodies contain elements. Thus, elements are the building block of all materials.

The examples of elements are copper, oxygen, hydrogen. The examples of compounds are water, sugar, salt, etc.

Homogeneous mixture examples are sugar + H2 O, water + alcohol. Heterogenous mixture examples are sand + sugar, water + oil.

In the modern periodic table, there are 118 elements known to us.

Out of 118 elements, 92 of which are naturally occurring while the remaining 26 have been artificially created. But from these 118 elements, crores of compounds are formed some naturally occurring and some artificial.

Robert Boyle used the name element for any substance that cannot be broken down further, into a simpler substance. This definition can be extended to include the fact that each element is made up of only one kind of atom. Eg., aluminium is an element which is made up of only aluminium atoms. It is not possible to obtain a simpler substance chemically from the aluminium atoms. You can only make more complicated substances from it, such as aluminium oxide, aluminium nitrate and aluminium sulphate.

The smallest unit of an element which may or may not have an independent existence, but always takes part in a chemical reaction is called atom.

The smallest unit of a pure substance, which always exists independently and can retain physical and chemical properties of that substance is called a molecule. Examples; Hydrogen molecule consists of two hydrogen atoms (H2 ) Water molecule consists of two hydrogen atoms (H2 ) and one oxygen atom (O).

All elements can be classified according to various properties. A simple way to do this is to classify them as metals, non-metals and metalloids. Examples of Metal are Copper, Chromium, Gold, Mercury. Example of Metalloid are Boron, Silicon, Germanium, Arsenic. Example of Non-metal are Carbon, Oxygen, Neon, Chlorine.

When two or more elements combine chemically to form a new substance, the new substance is called a compound.

The cane sugar is made up of three elements carbon, hydrogen and oxygen. The chemical forumula of cane sugar is C12 H22 O11.

A compound has properties that are different from those of the elements from which it is made. Common salt, also known as sodium chloride, is a compound. It is added to give taste to our food. It is a compound made up of a metal, sodium and a non-metal, chlorine.

Compounds of phosphorous, nitrogen and potassium are used in fertilizers.

Silicon compounds are of immense importance in the computer industry.

Compounds of fluorine are used in our toothpastes as they strengthen our teeth.

The property of elements is i) Made up of only one kind of atom, ii) The smallest particle that retains all its properties is an atom, and iii) Cannot be broken down into simpler substances.

A mixture is an impure substance. It contains two or more kinds of elements or compounds or both physically mixed together in any ratio. For, example, tap water is a mixture of water and some dissolved salts. Lemonade is a mixture of lemon juice, sugar and water. Air is a mixture of nitrogen, oxygen, carbon dioxide, water vapour and other gases. Alloys are mixtures of metals.

Liquefied Petroleum Gas is highly inflammable hydrocarbon gas. It contains mixture of butane and propane gases. LPG, liquefied through pressurisation, is used for heating, cooking, auto fuel etc.

Blood is not a pure substance. It is a mixture of various components such as platelets, red and white blood corpuscles and plasma.

Properties of Mixtures are i) It contains two or more substances, ii) The constituent may be present in any proportion. iii) They show the properties of their constituents. iv) The components may be separated easily by physical methods.

The properties of components are i) It is a single substance, ii) The constituents are present in definite proportions, iii) They do not show the properties of the constituent elements and iv) The constituents can only be separated by one or more chemical reactions.

Heterogeneous – Solid and solid, Insoluble solid and liquid, Two immiscible liquids.

The Methods of separation used for solid and solid mixtures are Handpicking, sieving, winnowing, magnetic separation, sublimation.

Certain solid substances when heated change directly from solid to gaseous state without attaining liquid state. The vapours when cooled give back the solid substance. This process is known as sublimation. Examples: Iodine, camphor, ammonium chloride etc.,

The pure vapours of the volatile solid pass through the holes in the asbestos sheet and condense on the inner sides of the funnel. The non-volatile impurities remain in the china dish.

The air fresheners are used in toilets. The solid slowly sublimes and releases the pleasant smell in the toilet over a certain period of time. Moth balls, made of naphthalene are used to drive away moths and some other insects. These also sublime over time.

The method of separations for Insoluble solid and liquid mixtures are Sedimentation and decantation, loading, filtration, centrifugation.

Centrifugation is the process by which fine insoluble solids from a solid- liquid mixture can be separated in a machine called a centrifuge. A centrifuge rotates at a very high speed. On being rotated by centrifugal force, the heavier solid particles move down and the lighter liquid remains at the top. In washing machines, this principle is used to squeeze out water from wet clothes. Centrifugation is also used in pathological laboratories to separate blood cells from a blood sample.

The methods of separations for soluble solid and liquid mixtures are Evaporation, distillation, crystallisation.

Distillation is a process of obtaining pure liquid from a solution. It is actually a combination of evaporation and condensation i.e., Distillation = Evaporation + Condensation.

Solvent extraction is an old practice done for years. It is the main process in perfume development and it is also used to obtain dyes from various sources.

The method of separation used for two miscible liquid mixtures are Fractional distillation.

Two immiscible liquids can be separated by solvent extraction method. This method works on the principle of difference in solubility of two immiscible liquids in a suitable solvent. For example, mixture of water and oil can be separated using a separating funnel. Solvent extraction method is used in pharmaceutical and petroleum industries.

To separate two or more miscible liquids which do not differ much in their boiling points (difference in boiling points is less than 25 K) fractional distillation is employed. Fractional distillation is used in petrochemical industry to obtain different fractions of petroleum, to separate the different gases from air, to distil alcohols etc.

Adsorption is the process in which the particles of a substance is concentrated only at the surface of another substance.

Chromatography is also a separation technique. It is used to separate different components of a mixture based on their different solubilities in the same solvent. There are several types of chromatography based on the above basic principles. The simplest type is paper chromatography.

Absorption is the process in which the substance is uniformly distributed throughout the bulk of another substance.
For example, when a chalk stick is dipped in ink, the surface retains the colour of the ink due to adsorption of coloured molecules while the solvent of the ink goes deeper into the stick due to absorption. Hence, on breaking the chalk stick, it is found to be white from inside.

The black ink separates into its constituent dyes. As the solvent moves up the paper, the dyes are carried with it and begin to separate. They separate because they have different solubility in the solvent and are adsorbed to different extents by the chromatography paper. The chromatogram shows that the black ink contains three dyes.

A solution is a homogeneous mixture of two or more substances. In a solution, the component present in lesser amount by weight is called solute and the component present in larger amount by weight is called solvent.
In short, a solution can be represented as follows: solute + solvent solution.

Based on the particle size of the solute, the solutions are divided into three types. They are 1. True solution, 2. Colloidal solution and 3. Suspension solution.

In the case of wheat flour mixed with water we get a very turbid mixture and fine particles slowly settle down at the bottom after some time. This mixture is called as suspension. The particle size greater than 10-5 cm.
In the case of starch and water we get a cloudy mixture. This mixture is called as colloidal solution. The particle size between 10-7 cm and 10-5 cm.

A colloidal solution is a heterogeneous system consisting of the dispersed phase and the dispersion medium. Dispersed phase or the dispersion medium can be a solid, or liquid or gas.

There are eight different combinations possible. The combination of gas in gas is not possible because gas in gas always forms a true solution.

The beam of light coming from headlights of vehicles is due to Tyndall effect. Blue colour of sky is also due to Tyndall effect.

Tyndall (1869) observed that when a strong beam of light is focused on a colloidal solution the path of the beam becomes visible. This phenomenon is known as Tyndall effect and the illuminated path is called Tyndall cone. This phenomenon is not observed in case of true solution.

When colloidal solutions are viewed under powerful microscope, it can be seen that colloidal particles are moving constantly and rapidly in zig-zag directions. The Brownian movement of colloidal particles is due to the unbalanced bombardment of the particles by the molecules of dispersion medium.

An emulsion is a colloid of two or more immiscible liquids where one liquid is dispersed in another liquid. This means one type of liquid particles get scattered in another liquid.

The word emulsion comes from the Latin word meaning “to-milk” (milk is one example of an emulsion of fat and water). Milk, butter, cream, egg yolk, paints, cough syrups, facial creams, pesticides etc. are some common examples of emulsions.

An emulsion is a special type of mixture made by combining two liquids that normally don’t mix. The process of turning a liquid mixture into an emulsion is called emulsification.