Distilled Water

Fig: Distillated Process

For ordinary lab use, water is distillated in a copper vessel or stainless steel vessel automatically heated by gas, flame or electricity. A pure sample is obtained by adding a little acidified potassium permanganate solution to ordinary distilled water and allowing the mixture to stand for a few hours. The water is then distilled; the distillate is mixed with a little barium hydroxide and redistilled using a tin condenser.

Advantages of Hard water

1.Hard water is advantageous for the strengthening the bones and teeth.

2.Due to the presence of soluble salts, water becomes tasty otherwise; it is a flap in taste.

3.Hard water is used in beer factory.

Disadvantages of Hard water

1.Large amount of soap is wasted while washing clothes in hard water because it does not produce lather readily.

2.White clothes become dull after regular washing in hard water.

3.When hard water is boiled scales are formed which reduces the life of the boiler.

           

Removal of Permanent Hardness

It is not easy to remove permanent hardness of water as temporary hardness. Permanent hardness can be removed by following methods.

a) Treatment with washing soda: 
       Soluble salts of calcium and magnesium turn into insoluble salts when washing soda (sodium carbonate) is mixed with it.

Fig: Washing soda

CaCl₂ + Na₂CO₃ = CaCO₃ + 2NaCl

MgSO₄ + Na₂CO₃ = MgCO₃ + Na₂SO₄

b) Permutit process: 
        Permutit is the trade name for an artificially prepared sodium zeolite or sodium aluminium orthosilicate obtained by fusing together sodium carbonate, silica and alumina. Its composition corresponds to Na₂Al₂Si₂O₈ or Na₂Z where Z stands for zeolite = Al₂Si₂O₈. It possesses remarkable property of reacting with calcium and magnesium ions forming insoluble calcium or magnesium zeolite. By passing hard water through a cylinder packed with permutit all the ions responsible for the hardness of water are drawn and replaced by sodium ions.

Ca-salt + Na-permutit = Ca-permutit + Na-salt

Mg-salt + Na-permutit  = Mg-permutit + Na-salt

In due course, however, the permutit is exhausted by having given up all its sodium ions. This can be regenerated by soaking in a 10% solution of common salt when the reverse change take place and calcium and magnesium ions pass into solution and sodium zeolite is formed again.

CaZ + 2NaCl = Na₂Z + CaCl₂

MgZ + 2Nacl = Mg₂Z + MgCl₂

Fig: Permutit process

The resulting calcium and magnesium chlorides are washed out and the regenerated permutit used over again.

Removal of Temporary Hardness of Water

As said earlier, temporary hardness of water can be removed easily. The following methods may be adopted for the removal of temporary hardness of water.

i) By boiling:  

Fig: Boiling water

A soluble bicarbonate salt of calcium and magnesium becomes insoluble salt on heating. The insoluble salt settles at the bottom of boiler.

Calcium hydrogen   =  calcium    +     carbon    + water.

            carbonate            carbonate       dioxide

Ca(HCO₃)₂ = CaCO₃ + CO₂ + H₂O

ii) Treatment with lime water : Temporary hardness of water can be removed by treating with lime water. This is known as Clark’s method.

fig: Clark's method of removing hardness of water

Carbonate + lime water = calcium carbonate + water

Ca (HCO₃)₂ + (Ca(OH)₂  = CaCO₃ + 2H₂O

Types of Water

a)Hard water

b)Soft water

Water dissolves may substances in it. There are some salts of calcium and magnesium when present causes hardness of water. Hard water does not produce lather with soap easily like soft water. From this we come to know which hard water is. In the boilers, scales are formed which is the deposit of salts of calcium or magnesium. This reduces the life of the boiler.

           

Hardness of water is due to the presence of salts of calcium and magnesium such as Calcium chloride (CaCl₂), Calcium sulphate (CaSO₄), Calcium bicarbonate (Ca (HCO₃)₂), Magnesium chloride (MgCl₂), Magnesium sulphate (MgSO₄), Magnesium bicarbonate (Mg (HCO₃)2). Water which gives lather easily with soap is soft water.

There are two types of hardness of water. They are:

1.Temporary hardness

2.Permanent hardness

Temporary Hardness

            Temporary hardness of is due to the presence of bicarbonate salt of calcium and magnesium such as calcium bicarbonate and magnesium bicarbonate.

Permanent Hardness

Permanent hardness is due to the presence of chlorides and sulphates of calcium and magnesium such as calcium chloride, magnesium chloride, calcium sulphate and magnesium sulphate in water.

Hardness of water can be removed by various methods.

Air

Air is a mixture of different gases and water vapour. It covers the earth. The thick layer of air that surrounds the earth is called atmosphere. The atmosphere lies within 16 km from the earth’s surface. It also contains dust particles. The air is also found in the soil, water and porous materials such as sponges, bricks, wood, breads, etc. It cannot be seen but can be felt. Living things cannot survive without air. It is the most important things to all the living things. All the living things take in oxygen from the air and give out carbon dioxide during respiration. All the green plants use carbon dioxide of the air to make their food during photosynthesis.

           

Composition of air

            We learn that air is mixture of gases. The main gases of air are nitrogen and oxygen. Nearly four-fifth of the air is nitrogen and oxygen whereas one-fifth of air contains oxygen. Besides these gases, the other gases present in the air are carbon dioxide, water vapour and the inert gases like neon, argon, helium, krypton, xenon and radon.

            The given figure shows the composition of the air on the earth. Plants use nitrogen in the form of fertilizer. Carbon dioxide and oxygen gases are exchanged between atmosphere and photosynthesis. Carbon dioxide is formed in the air by the combustion of fuel. In this way, the composition of the gases in the atmosphere is generally constant everywhere on the earth. However, the amount of water vapour and carbon dioxide may differ from place to place.

            Various activities have shown that the composition of air on the earth by volume is as given in the table.

S.N	Gases in air	Percentage by volume
1. 2. 3. 4. 5. 6. 7.	Nitrogen Oxygen Carbon dioxide Argon Neon Other inert gases Water vapour	78.07 20.98 0.03 0.85 0.002 0.008 0.06

Rusting

Fig: Rusting of iron

            We may have noticed that when shiny iron rods are exposed in a moist place for few days, their outer surface becomes reddish brown. The reddish brown layer on the surface of the iron rod is called rust. This brown rust is reddish due to the oxides of the iron. Thus, the process of formation of rust by the slow oxidation of iron into oxide due to the atmospheric oxygen in the presence of water vapour is called rusting.

Presence of oxygen in air

White phosphorus powder glows green in the presence of oxygen.

           Oxygen is an important gas found in the air.  It constitutes one fifth of the air by volume. All the living thing uses it during the process of respiration. Oxygen in the air also helps in the process of burning.

Carbon dioxide in air

Fig: Carbon dioxide in air

            Carbon dioxide in the air is used by plants to make their food during  the process of photosynthesis. It is given off during the process of respiration by all living things. It is also produced when fuels are burnt in air.

Properties of air

1.Air is mixture of different gases. It is composed of nitrogen, oxygen, carbon dioxide, inert gases and water vapour.

2.Air occupies spaces and has weight.

3.Pure air is colorless, tasteless and odorless.

4.Air exerts pressure and can be compressed.

5.Air can blow from one place to another.

6.Air expands on heating.

Uses of air

1.Air helps to burn things as it contains oxygen. Oxygen is a supporter of burning.

2.Almost the all animals and plants use oxygen during the process of respiration.

3.All the green plants take carbon dioxide to prepare their food during the process of photosynthesis.

4.All the living things need nitrogen. It is the most essential gas that is used to make protein by all the living things. Proteins are essential for life.

5.The larger amount of nitrogen in the air prevents constant fire as it is neither a combustible nor a burning supporter.

6.Air is used to fill in the tires of vehicles, bladder of football, etc.

7.Air helps in the dispersal of seeds and pollination of flowers.

8.The moving air is used in wind-mills as it is a source of energy.

Solubility of Substance

            Scientists have found that all the substances of same weight cannot be dissolved in the same quantity of water at a particular temperature. “The solubility of a substance at a given temperature is defined as the quantity of the substance that can be dissolved in 100 parts of the solvent at that temperature to give a saturated solution”. It means, solubility of a substance at a particular temperature is fixed. Different substances have different solubility at the same temperature.

            At 30°C, 25gm of copper sulphate (CuSO₄) dissolved in 100gms of water forms a saturated solution. The solubility of copper sulphate is 25gm. Similarly, the solubility of potassium nitrate (KNO₃) is 46 gm, sodium chloride (NaCl) is 36gm, sugar is 220gm and sodium nitrate (NaNO₃) is 95gm. The solubility of different substance differs according to the temperature can be understood from below table:

S.N	Name of substance	Temp°C	Solubility gm/100gm water
1. 2. 3. 4. 5.	Copper sulphate Potassium nitrate Sodium chloride Sugar Sodium nitrate	30 30 30 30 30	25 46 36 220 95

           

            The solubility of a substance can be obtained by using the following relationship:

                                Solubility = 100 × Wt. of solute (gm)

                                                               Wt. of solvent (gm)

Example: Find the solubility of sugar if 5.1 gm of it when completely dissolved in 2.5gm of water at 20°C forms saturated.

Solution:

            Here,

            Wt. of solute = 5.1 gm

            Wt. of solvent = 2.5 gm

            Temperature = 20°C

            Solubility =?

We have,

Solubility = 100 × Wt. of solute (gm)

                                Wt. of solvent (gm)

                        = 100×5.1

                                     2.5

                        = 204

Solubility of sugar at 20°C is 204.

Solubility Curves:

            Scientists have found that the solubility of a particular substance is not same at different temperatures. The capacity of solvent to dissolve a substance depends upon the temperature. Therefore, solubility of a substance also depends upon the temperature. Solubility differs according to the change in temperature. This can be understood from solubility curves.

            The solubility of a substance at different temperature when plotted on a graph, we can get a line or curve called solubility curve. In solubility curve, the temperature is plotted on X-axis and solubility against that temperature on Y-axis.

Fig: solubility curve

            A curve obtained by plotting the solubility of a substance at different temperatures against these temperature is known as solubility curve.

            It is observed that in most cases the solubility rises with the temperature. This rise in solubility varies for different substances. It the curve shows the break, it suggests formation of a new hydrate.

Information from solubility curves:

            The solubility curves give us valuable information. These are listed below:

1. At a glance, we know the solubility at different temperature.

2. Solubility of a substance increases with temperature.

3. Solubility of different substances can be compared.

4. If two or more solutes are present, we know which one will crystallize first.

5. Temperature of formation of hydrate is indicated.

Oxygen Gas

Symbol: O          

Molecular formula: O₂

Molecular weight: 16

Fig: Electronic configuration of oxygen

Discovery

Oxygen is one of the abundantly available gases in air. It makes about 21% of atmosphere by volume. It is important to all the life on earth. It was discovered by a Swedish chemist Scheele in 1772 by heating red oxide of mercury and by Priestley of England in 1774. Antony Lavoisier of France studied its properties and named as ‘Oxygen’ in 1776. The credit of discovery goes to Joseph Priestley because his papers were published earlier.

               Oxygen is available in free state in air. It forms a mixture with other gases to form air. In combined state, it is present in oxides. It combines with many elements to form compounds such as sugar, starch, fats and oils, acid, bases and salts. It is found in maximum quantity upon the earth in oxides of metals and non-metals.

Laboratory preparation of Oxygen (using heat)

Apparatus required:

1.      Hard glass test-tube.

2.      Delivery tube.

3.      Trough with water

4.      Gas jar

Chemical required:

1.      Potassium chlorate (KClO₃)

2.      Manganese dioxide (MnO₂)

Water

Molecular formula: H₂O

Molecular weight: 18

Introduction

            From the origin of the earth water is present on the earth. In Hindu mythology water is an element of constituent of life. But modern science has revealed that water is compound of Hydrogen and oxygen combined in 1:8 ratios.

Water has three states: solid, liquid and gas (vapour) according to the temperature. At normal temperature it is found in liquid state but when it is cooled less than 0 C, it becomes ice (solid state) and at higher temperatures it becomes vapour (gas state). Water has a special property. When heated from 0C to 4C its density increases and occupies less volume. This is known as anomalous property of water.

            Water is known as universal solvent since it dissolves many substances. Without water life is not possible. Water content in human body is 70%, in fishes 80%, in vegetables 90-95% by weight.

            Water is used in drinking, cleaning utensils, washing. Cooking, cooling in industries, etc. For different purposes water is used in pure form. For the chemical reactions in the lab, it is used in very pure form.

Nitrogen Gas

Fig:electronic configuration

Symbol: N

Molecular formula: N₂

Atomic number: 7

Atomic number: 14                                               

Position in the Periodic Table: Group 5

Electronic configuration: 2, 5  

Discovery

            Nitrogen gas was discovered in 1772 by Daniel Rutherford, a Scottish physician and chemist. He obtained it by burning phosphorous in enclosed air. Lavoisier studied its properties in detail and showed that it does not support combustion and respiration and for this reason called azote (Greek; a = no, zoe = life).

            Nitrogen is one of the gases found in nature in abundant quantity. It occupies about 78% by volume. It is also found in combined state in proteins (meat, fish, egg and pulses) and nitrate salts.

            Nitrogen is an essential constituent of animal and plant life. The atmospheric nitrogen goes in cycle so that the natural balance of atmosphere air is possible. The nitrogen cycle is given below.

Fig: nitrogen cycle

Preparation of Nitrogen gas

From air

Nitrogen gas can be prepared from air by burning phosphorous. A small crucible is placed on a cork floating in water. The phosphorous is ignited and the crucible covered immediately by a gas jar. The oxygen present in the jar combines with phosphorous to form phosphorous pentoxide which dissolves in water and the level of water rises in the jar. The gas remaining in the jar is nitrogen.

P₄ + 5H₂O = 2P₂O₅

P₂O₅ + 3H₂O = 2H₃PO₄

Nitrogen can be prepared by passing air over red hot copper which combines with the oxygen present in the air to form copper oxide and the nitrogen present can be collected over water.

Laboratory preparation of Nitrogen gas

           

Apparatus required:

1.Round bottomed flask

2.Burner

3.Delivery tube

4.Trough

5.Beehive shelf

6.Gas jar

Chemical required

1.Ammonium chloride (NH₄Cl)

2.Sodium nitrite (NaNO₂)

Principle

            A mixture of ammonium chloride and sodium nitrite when heated, nitrogen gas will be produced which can be collected by downward displacement of water.

            NH₄Cl + NaNO₂ = NaCl + N₂ + 2H₂O

          

  Procedure

The apparatus is fitted as shown in the figure. When the mixture of ammonium chloride and sodium chloride is heated it begins to decompose. Nitrogen bubbles displace water in the gas jar. Thus nitrogen gas can be collected by downward displacement of water.

Manufacture of Nitrogen gas

            At industrial level, nitrogen is manufactured from air. Air is a mixture of different gases where nitrogen has higher percentage by volume. This nitrogen can be separated from air.

            Atmospheric air is cooled down so that all gases are liquefied. The liquid air is cooled down so that nitrogen boils (nitrogen has lower boiling point than other gases). Nitrogen vapour is collected in the cylinders and sent for use. 

Properties of Nitrogen gas

            Physical properties:

1.Nitrogen is a colorless, odorless and tasteless gas.

2.It is slightly lighter than air. Its density is 14 while that of air is 14.4.

3.It is insoluble in water.

4.It is non-poisonous but animals die in an atmosphere of nitrogen for want of oxygen.

Chemical properties:

1.It is neutral to litmus.

2.Nitrogen is incombustible and a non-support of combustion but burning magnesium or aluminium continues burning in an atmosphere of nitrogen forming nitrides.

3Mg + N₂ = Mg₃N₂

2Al + N₂ = 2AlN

3.With oxygen it combines only in the presence of lighting discharge or when the mixture is passed through an electric arc.

N₂ + O₂ = 2NO

4.With hydrogen it combines under pressure (200 atmospheres) and in the presence of catalyst (finely divided iron + molybdenum at 500◦C).

N₂ + 3H₂ = 2NH₃

Use of Nitrogen gas

1.Nitrogen gas is used to prepare Ammonia, nitric acid and explosives.

2.Nitrogen gas is used in aeroplane to prevent formation of explosive mixture by combination of fuel and atmospheric air.