Is Matter Around Us Pure

A pure substance is a type of substance which constitute of only single type of particles and are homogeneous in nature (i.e same physical and chemical properties). Example:- Sulphur gas is made up of only one kind of Particles called Sulphur .

The main points of difference between homogeneous mixtures and heterogeneous mixtures are as follows:

• The mixtures in which the substances are completely mixed together and are indistinguishable from each other are called homogeneous mixtures.
• A homogeneous mixture has a uniform composition throughout its mass.
• All the homogeneous mixtures are called solutions.
• For example, a mixture of alcohol and water is a homogeneous mixture.

• A mixture which does not have a uniform composition throughout its mass.
• It has visible boundaries of separation between the various constituents.
• They consist of more than one phase.
• For example, a mixture of water and sand is a heterogeneous mixture.

Sol, solution and suspension are different from each other in the following ways:

The concentration = Mass of solute / Mass of solution X 100

Concentration = (36/136) x 100

= 26.47%

Chemical changes are rusting of almirahs, passing of electric current through water and water breaking down into hydrogen and oxygen gases, burning of paper and wood. The chemical properties of all of these substances have changed and new substances have been formed as a result of these changes. Rust is an oxide of iron which is a new substance formed on the surface of almirah. Hydrogen and oxygen are also new compounds which are produced after passing electric current through water. Burning of paper is a chemical reaction which has changed in the chemical properties of paper.

Physical changes are melting of butter in a pan, cutting of trees, boiling of water to form steam, dissolving common salt in water and making a fruit salad with raw fruits. Physical changes occur without any change in chemical composition of a substance. Melting butter and boiling of water to form steam has only changed the physical states of these substances without causing any change in their chemical composition.

1. When the difference in the boiling points of two miscible liquids is 25°C or more, they can be separated by the process of ‘Simple Distillation’.
2. In this case, the difference in the boiling points of kerosene and petrol is 25°C. Therefore, a mixture containing kerosene and petrol can be separated by the process of simple distillation.
3. This can be done as follows:

• The mixture of kerosene and petrol is taken in a distillation flask fitted with a thermometer and a water condenser.
• The distillation flask is heated with a burner.
• Petrol will vaporise first as it has lower boiling point than kerosine. It will be condensed in the condenser and will be collected in the condenser outlet. Kerosene will be left behind in the distillation flask.

(i) Butter can be separated from curd by the process of Centrifugation. The principle behind this process is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

(ii) Salt can be separated from seawater by the process of Evaporation. Seawater is boiled or evaporated. After evaporation salt is left behind.

(iii) Camphor can be separated from salt by the process of sublimation. This mixture is heated and camphor being the volatile component is separated in the form of vapours.

Some of the things around us are: Tap water, Milk, Naphthalene balls, Sodium chloride, Air, Gold ornaments, Ice-cream, Steel, Distilled water, Diamond, Steam, Kerosene oil, Alum, Salt solution, Brass, Alcohol, Vinegar. Graphite, Wood and Baking soda. We can segregate (or separate) these things as pure substances or mixture of as shown below:

A pure substance is made up of only one kind of particles. All the constituent particles of a pure substance are the same in their chemical nature. These particles may be atoms or molecules. All the elements and compounds are pure substances because they contain only one kind of particles. A pure substance cannot be separated into other kinds of matter by any physical process.

A mixture contains more than one substance, element and/or compound mixed in any proportion. Mixtures can be separated into pure substances using appropriate separation techniques.

The process in which a pure solid is separated from a solution in the form of its crystals is called Crystallisation. Crystallisation is a method which is used to purify the solids. The mixtures containing solids in which the impurities may be either 'less soluble' in the solvent or 'more soluble' in the solvent than the solids, are separated by the technique of crystallisation. For example, the impurities present in impure copper sulphate, common salt and alum, etc., can be separated by this technique crystallisation to obtain the pure substances.

(a) Sodium chloride can be separated from its solution in water by the process of Evaporation. This solution is boiled or evaporated. After evaporation sodium chloride will be left behind.

(b) Ammonium chloride can be separated from a mixture containing sodium chloride and ammonium chloride by the process of ‘Sublimation’. On heating this mixture, ammonium chloride changes directly from solid to gaseous state leaving behind sodium chloride. During this process, the solids form of ammonium chloride can be collected on the sides of the funnel.

(c) Small pieces of metal in the engine oil of a car can be separated by the process of ‘Filtration’.

(d) Different pigments from an extract of flower petals can be separated by the process of ‘Chromatography’. Chromatography is the technique which is used for separation of those solutes that dissolve in the same solvent.

(e) Butter can be separated from curd by the process of Centrifugation. The principle behind this process is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

(f) Oil can be separated from water by using ‘Separating funnel’. Mixture of oil and water are poured in the funnel and are allowed to stand undisturbed for sometime. This results in the formation of separate layers of water and oil.

(g) Tea leaves from tea can be separated by filtration.

(h) Iron pins can be separated from sand by using a magnet.

(i) Wheat grains can be separated from husk by Winnowing. It is a very simple process in which the wheat grains are thrown into the air, so that the wind blows away the lighter husk.

(j) Mud particles suspended in water can be removed by decantation and filtration.

Tea can be prepared by the following steps:

1) Take a cup of water in a pan and heat it on a gas burner. The water acts as a solvent. Allow the water to boil.

2) Now add a spoonful of sugar in the water. Sugar is a solute. Heat till all the sugar is dissolved in water.

3) We will get a solution of sugar and water.

4) To the solution of sugar and water add a teaspoon of tea leaves. Tealeaves are insoluble in water.

5) Allow the contents to boil and then add milk to the solution and boil again. Milk is also soluble in water.

6) Filter the tea leaves from the solution with the help of a strainer. Hot tea which is collected in the cup is the filtrate and the tea leaves left on the strainer is the residue.

(a) Mass of KNO₃ to produce a saturated solution of KNO₃ in 100 gm of water at 313 K = 62 g

Therefore, mass of KNO₃ in 50 g of water at 313 K = 62.050/100 = 31.0 g

31 g of potassium nitrate is needed to produce a saturated solution of potassium nitrate at 313 K.

(b) When the saturated solution of potassium chloride is left to cool at room temperature, then solid potassium chloride will separate gradually from the solution. Solubility of a substance depends on the temperature. Solubility increases with increase in temperature of the solution. Room temperature is lower than 313 K hence, the crystals of solute will separate out from the solution.

(c) The solubility of different salts at 293 K is: Potassium nitrate 32g ; Sodium chloride 36g; Potassium chloride 35g; and Ammonium chloride 37g. Ammonium chloride has the highest solubility of 37 g at 293 K.

(d) Solubility of a substance depends on the temperature. The given data shows that the solubility of a salt increases on increasing the temperature.

(a) In a solution the relative proportion of the solute and solvent can be varied. At a given temperature, when no more solute can be dissolved in a solution, it is called a saturated solution. The amount of the solute present in the saturated solution at this temperature is called its solubility. For example, In order to obtain a saturated solution of sodium chloride and water at 20°C, a maximum of 36 grams of sodium chloride can be dissolved in 100 grams of water.

(b) A pure substance is made up of only one kind of particles. All the constituent particles of a pure substance are the same in their chemical nature. These particles may be atoms or molecules. For example, sulphur is made up of only one kind of particles called sulphur atoms, therefore, sulphur is a pure substance.

(c) A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and suspensions. Due to the relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous. But actually, a colloidal solution is a heterogeneous mixture, for example, milk.

(d) A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension can be seen with naked eye. The particles of a suspension are able to scatter a beam of light passing through them and make its path visible. When left undisturbed, the solute particles are able to settle down. This shows that a suspension is unstable. They can be separated from the mixture by the process of filtration.

Homogenous mixture: The mixtures in which the substances are completely mixed together and are indistinguishable from each other are called homogeneous mixtures. A homogeneous mixture has a uniform composition throughout its mass. It has no visible boundaries of separation between the various constituents. A mixture of two or more miscible liquids is also a homogeneous mixture. All the homogeneous mixtures are called solutions. They consist of only one phase.

Heterogeneous mixture: A mixtures which does not have a uniform composition throughout its mass. It has visible boundaries of separation between the various constituents. The constituents of a heterogeneous mixture can usually be seen easily. They consist of more than one phase. A mixture of two or more immiscible liquids is also a heterogeneous mixture. For example, a mixture of petrol and water is a heterogeneous mixture.

A pure substance is made up of only one kind of particles. All the constituent particles of a pure substance are the same in their chemical nature. These particles may be atoms or molecules. Pure substances have fixed melting or boiling point. In order to confirm that a colourless liquid is pure water, we can check its boiling point. Pure water boils at 100°C at atmospheric pressure. If this liquid also boils at 100°C then its is pure water.

A pure substance is made up of only one kind of particles. All the constituent particles of a pure substance are the same in their chemical nature. These particles may be atoms or molecules. All the elements and compounds are pure substances because they contain only one kind of particles. A pure substance cannot be separated into other kinds of matter by any physical process. A pure substance has a fixed composition as well as a fixed melting point and boiling point.

Pure substances are: Ice, Iron, Hydrochloric Acid, Calcium oxide and Mercury. All these substances are pure because these are made of same kind of atoms or molecules. They have fixed melting or boiling points.

On the other hand, Brick, Air, Milk and wood are not pure substances because all of these do not have a fixed composition. Air is a mixture of gases in which the composition of gases is not fixed. Milk is a colloidal solution.

Milk and Starch solution are capable of showing "Tyndall effect" because these are colloidal solutions.

A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and suspensions. Due to the relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous. But actually, a colloidal solution is a heterogeneous mixture, for example, milk. Because of the small size of colloidal particles, we cannot see them with naked eyes. But, these particles can easily scatter a beam of visible light known as "Tyndall effect".

Growth of a plant, Rusting of iron, Cooking of food, Digestion of food and Burning of a candle are chemical changes.

Chemical change brings change in the chemical properties of matter and a new substances is formed. A chemical change is also called a chemical reaction. All of the above changes have resulted in the formation of new substances as a result of chemical reactions.