You have learnt about units of measurement in the previous lesson. What we eat, drink or breathe is the matter. Hence all of us are surrounded by matter. Anything which occupies space and has mass is matter. In order to understand the world better it is necessary to understand the nature of matter. In this section you shall learn about matter and shall utilise the concepts of measurement in understanding the properties of matter.

OBJECTIVES

• After completing this lesson you will be able to:
• describe what is matter and explain its particulate nature;
• clarify and differentiate the three states of matter – solid, liquid and gas;
• describe the effect of pressure and temperature on states of matter;
• illustrate the inter-conversion of these states with the help of suitable examples;
• classify the given matter as an element, a compound or a mixture;
• distinguish between homogeneous and heterogeneous mixtures;
• define the terms solution, solvent and solute; calculate the percentage composition of a solution;
• describe the properties and uses of suspension, and describe the common methods used for separation of mixtures or purification of a substance.

WHAT IS MATTER?

Matter is any thing which has mass and occupies space. All solids, liquids and gases around us are made of matter. Scientist believe that matter is made of tiny particles that clump together. You cannot see these particles but you can see the matter, for example, a book, a car, a letter, a hand set, a piece of wood, tree, a bag etc. Think and add a few more examples from your day to day life.

PARTICULATE NATURE OF MATTER

Human beings have been questioning the nature of matter. In ancient times there were two different views about it. One school of thought believed that if we take a piece of matter (for example stone) and break it into smaller pieces and break these smaller pieces into still smaller pieces, the process can be repeated any number of times. This would happen because matter is continuous and its piece of any size can be broken or subdivided into smaller pieces. Greek philosophers Plato and Aristotle belong to this school of thought. The second school of thought believed that process of subdivision of matter can be repeated only for limited number of times. A stage would be reached when the tiny particles of matter so obtained cannot be further subdivided. They believed that all matter is composed of very tiny particles. In other words, the matter has particulate nature. The smallest indivisible particles of matter were given the name “atom” from the Greek word “Atomos” for “ indivisible

STATES OF MATTER Matter

can be classified in many ways. However, the following are the two main ways of classifying the matter:

(i) by the physical state of matter as a solid, liquid, or gas, and

(ii) by the chemical composition of matter as an element, compound or mixture.

We shall discuss these classifications in the next section.

Let us discuss about the classification of matter based on physical states. Matter can ordinarily exist in three states –solid, liquid and gas. These three states of matter have different properties. Water exists in all the three states namely steam or water vapour (gas), water at room temperature (liquid) and ice (solid). This is the only substance which exists naturally in all the three states.

The characteristic properties of different states of matter depend on intermolecular forces. The forces holding molecules together are called intermolecular forces. Intermolecular forces (i.e. forces between the constituent molecules) try to keep molecules together but thermal energy always tries to keep them far apart. It is the competition between molecular interaction energy and thermal energy that decides whether a given substance under given conditions will be a solid, liquid or gas. Thermal or heat energy can convert one state of matter into another state. Thus a particular state of a matter depends on both : intermolecular force and the thermal energy which basically depends upon temperature.

Matter In Our Surroundings (part 1st)

Solids

We are surrounded by innumerable solid objects. A piece of wood, a stone, a pencil, a pen, and a computer all are examples of solids. A solid has definite size and shape which do not change on their own (see Fig.2.1). However, by using external forces you can change the shape of a solid. For example you can cut a piece of metal into two and you can use hammer to change its shape. Can you think of any other way to change the shape of solids? Yes, you can. Beat it into sheets or pull it into strings.

Liquids

Water is a liquid. Mustard oil and kerosene oil are other examples of liquids. Can you think of some more examples? A liquid has a definite volume. However, a liquid does not have a definite shape. It takes the shape of its container. A liquid can flow. You can pour a liquid or spill it. Can you spill a solid?

Liquids have properties intermediate between solids and gases. The intermolecular forces in liquids are weaker than solids but stronger than gases. In liquids the constituent particles do not occupy fixed position as in solids, but they have freedom of movement as in gases. In liquids intermolecular forces are stronger than those of gases.The constituent particles (atoms and molecules) in a liquid can break away from each other and get attracted while approaching the other molecules. Like in solids the intermolecular forces become repulsive when an attempt is made to bring the molecules closer  applying pressure. This is the reason why pressure does not have much effect on volume of liquids.

Gases

We cannot see gases but they are all around us. We can feel the presence of air when the wind blows. The wind is moving air and is a mixture of many gases like oxygen, nitrogen, argon, carbon dioxide and others. A gas occupies the entire volume of the container irrespective of its size In gases, molecules move freely because the intermolecular forces are very weak and are unable to keep the gas molecules together in bulk. The molecules remain far apart from each other due to weak molecular interactions. Since molecules are far away from each other in gases, they can be brought closer when pressure is applied. This is the reason why-gases are highly compressible. We can compress a gas only up to a certain limit. Beyond this limit repulsion between gas molecules becomes very high. Temperature also affects the volume of the gases. When temperature increases, volume of the gas also increases. For example when a closed container is heated it blasts due to rapid increase in volume.

EFFECT OF TEMPERATURE AND PRESSURE ON STATES OF MATTER

Have you ever thought what happens if a solid substance is heated? When heat is supplied to a solid, it expands. This expansion is very small. In fact after receiving thermal energy, particles (atom/molecules) vibrate more rapidly in their position and take up more space. If particles become more energetic on further heating they leave their fixed positions and the solid melts. Once a solid becomes liquid it can be poured into a container. As you learned earlier, a liquid takes the shape of the container in which it is poured. Particles in the liquid state are free to move.

Now let us see what happens when a liquid is heated. On receiving heat (thermal energy) a liquid is converted into a gas. This happens because the kinetic energy of the particles becomes so high that they can overcome the intermolecular force within the liquid. Therefore liquid is converted into gas (vapour)

ELEMENTS, COMPOUNDS AND MIXTURES

Matter In Our Surroundings (part 2nd)

Compounds

A compound is a substance formed when two or more than two elements arevchemically combined. A compound can be defined as a pure substance madevfrom two or more elements chemically combined together in a definite proportion by mass. When elements join to form compounds they lose their individual properties. Compounds have different properties from the elements they are made of. For example, water (a compound) is made up of elements – hydrogen and oxygen but properties of water are different from those of hydrogen and oxygen

.The world of compounds is really fascinating because compounds show a great

variety in forms and properties.

Some examples of compounds are given below:

Glucose Glycerol Calcium oxide

Sodium chloride Sulphuric acid Carbon dioxide

Hydrochloric acid Chloroform Acetic acid

Sodium carbonate Ethanol Carbon monoxide

Phenol Citric acid Methane

HOMOGENEOUS AND HETEROGENEOUS MIXTURES

SOLUTION AND ITS CONCENTRATION

A solution (a homogeneous mixture) is formed when one or more substances (the solute) are completely dissolved in another substance (the solvent). When we think about solutions, the most common examples that come to our mind are the solutions that are obtained by dissolving solids in water. Sugar or common salt dissolved

water gives this type of solution. Do you know that two-third of the Earth’s surface is covered by a solution? You may be able to guess this solution present in oceans. The sea-water is a solution of water and soluble minerals. It also contains gases like oxygen, nitrogen and carbon dioxide. Such dissolved gases are very important for aquatic life to survive in oceans.

There are some solutions of two or more than two liquids. As you know that ethyl alcohol mixes with water in all proportions to form a solution. Iodine (solid) dissolved in ethyl alcohol gives tincture of iodine which has antiseptic properties.

• A solution made of solid dissolved in a liquid has two parts:
• the solid that dissolves is called the solute, the liquid, in which the solid is dissolved, is called the solvent

SUSPENSIONS

In winter, the fog is a common experience in both urban and rural areas. What is fog? Fog forms when tiny water droplets are suspended in air. So fog is nothing but a type of a suspension. There are large numbers of substances which do not mix with each other. There are some solids that do not dissolve in water or other liquid solvents and there are liquids that do not mix with each other. The mixing of such substances results into heterogeneous mixtures. Depending on the size of the particles suspended, or dispersed in the surrounding medium, heterogeneous mixtures can be divided into colloids and suspension. You will study about colloids in higher classes. Here we shall briefly describe suspension. Materials of smaller particle size, insoluble in a solvent but visible to naked eyes, form suspension.

SEPARATION OF MIXTURES

Have you seen someone removing unwanted materials from rice or wheat? If so then you have seen separation of heterogeneous mixture into pure components by physical means. Have you eaten mishri, the bigger crystal of sugar? Preparation of mishri involves separation of sugar from homogeneous mixture of sugar and water. Both in our households and in industries we need to separate mixtures, both homogeneous and heterogeneous, for various purposes. Fortunately we can recover sugar or salt from its water solution by evaporating the water or even sometimes by heating. To separate different components of a mixture variety of physical techniques are available. All these separation techniques are based on difference in the physical properties of the components present in the mixture. The following two factors decide the best possible technique to be adopted for separation:

(i) the type of mixture,

(ii) the component which you want to collect.

Here we shall describe some of the common techniques of separation

Matter In Our Surroundings (part 3rd)

Separation by using Separating Funnels

The mixture of two immiscible liquids (i.e, the liquids that do not mix , as oil and water) can be separated by using a separating funnel. The mixture is placed in separating funnel and allowed to stand for some times. When the two layers of liquids

are separated, the denser liquid which is in the lower part, is first collected by opening

the stop-cock. This method is very useful in industries.

Separation by Evaporation

The separation of liquid (solvent) and solid (solute) from a solution is done by removing the liquid (solvent) by heating or by solar evaporation. By evaporation you can recover the solute component only in solid or powder form. If the solvent is inflammable you cannot use flame for heating instead you can use an electrical heating system and an oil or water bath. You might have heard that salt is obtained from sea water by the process of evaporation in shallow beds near the sea shore.

Separation by Filtration

Filtration is a better method for separating solids from liquids in heterogeneous mixtures. In filtration the solid material is collected as a residue on filter paper and the liquid phase is obtained as filtrate. The method of filtration is used on a large scale in industries

Separation by Crystallization Crystallization

is a process of formation of solid crystals from a solution. The method of crystallization for separating solid from liquid begins by evaporating the liquid. However, in crystallization, the evaporation is stopped when the solution is

concentrated enough. The concentrated solution thus produced, is allowed to cool

slowly to form crystals which can be separated by filtration. Mishri (sugar crystals) is produced by crystallization from concentrated sugar

Separation by Distillation

The method of distillation is used to separate a liquid from a solution of a homogeneous mixture. The distillation is a process in which a liquid or mixture of liquids is boiled in a distillation flask. The vapour is condensed by passing through a water-cooled tube called condenser and collected as liquid called distillate Fig. 2.14. In case of a solution of two miscible liquids (the liquids which can be mixed completely) the separation is based on the fact that the liquids will have different boiling points and there is a wide difference between the boiling points of the two liquids

Separation based on Magnetic Properties

How would you separate a mixture of magnetic and non-magnetic substance? In a mixture of magnetic and non-magnetic substances, the magnetic substance can be separated by using a magnet. For example you will be able to separate iron granules, which are magnetic, from non-magnetic substances like sand, sugar, saw dust etc. (Fig. 2.15). In industry this method is used to separate iron materials from nonmagnetic materials by using large electromagnets. e.g. of iron ore

Matter In Our Surroundings (part 4th)