AMMONIA

Molecular formula: NH₃

Molecular weight: 17

Occurrence

            Small quantities of ammonia are found in a place where nitrogenous decay takes place. In combined form it is found in Ammonium chloride and Ammonium sulphate naturally.

            Ammonia is a compound and it has molecular weight and molecular formula which has been given above. It forms by combining 1 atom of nitrogen and 3 atoms of hydrogen.

Laboratory preparation of Ammonia gas

            Ammonia gas is prepared in the laboratory by heating a mixture of ammonium chloride and slaked lime (calcium hydroxide).

            2NH₄Cl + Ca (OH)₂ = CaCl₂ + 2NH₃ + 2H₂O

Experiment: Powdered ammonium chloride many be mixed with slaked lime (calcium hydroxide) at the ratio of 2:1. The mixture may be put in a flask or hard glass test tube. Fit a cork at the mouth of the test tube with a delivery tube directing upwards which leads the gas in a jar which is inverted. The gas is lighter than the air and it is collected by downward displacement of air. When the test tube is heated the gas is liberated and collected in a gas jar. To test whether the jar is filled bring a moist red litmus paper. This turns into blue.

Fig: Lab preparation of ammonia gas.

Manufacture of Ammonia

            In industrial scale, ammonia gas is prepared by Haber’s Synthetic process. By laboratory process of preparation of ammonia gas we cannot fulfill the demand as it is required in the production of nitrogen rich fertilizers such as Ammonium sulphate.

Fig: Haber's synthetic process of preparation of Ammonia gas.

            

 A mixture of one volume of nitrogen and three volumes of hydrogen in a dry state is passed under a pressure of 200 atmospheres through a chamber of packed catalyst consisting of finely divided iron with a little of molybdenum and maintained at about 500◦C . The two gases combine under these conditions to form about 10% of ammonia.

            N₂ + 3H₂ = 2NH₃ + 22,500 cals

            The resulting mixture is passed through a coil maintained a very low temperature to condense the ammonia and the remaining uncombined gases are again passed through the catalyst chamber.

            In conclusion, the following conditions are required for the preparation of ammonia by Haber’s process.

1.One volume of Nitrogen and three volume of hydrogen flow.

2.Pressure of 200 atmospheres.

3.Temperature of 500◦C .

4.Catalyst, finely divided iron with a little of molybdenum.

Properties of Ammonia Gas

            Physical properties:

1. Ammonia is colorless gas.

2. It has pungent smelling and brings tears into the eyes.

3. It is poisonous.

4. It is lighter than air.

5. It is highly soluble in water.

Chemical properties:

1. It is basic in nature and therefore turns red litmus paper into blue.

2. Ammonia dissolves in water and produces hydroxide (ammonium hydroxide).

Ammonium hydroxide is a base and when it is treated with sulphuric acid, produces ammonium sulphate, a chemical fertilizer.

2NH₄OH + H₂SO₄ = (NH₄OH)₂ SO₄ + 2H₂O

3. Ammonia reacts with hydrogen chloride and produces dense white fumes of ammonium chloride. This property of ammonia is the sure test of gas.

NH₃ + HCl = NH₄Cl

Uses of Ammonia gas

1. In the manufacture of Urea and ammonium sulphate (chemical fertilizer) ammonia is extensively used.

2. Ammonia is used in the manufacture of nitric acid (Ostwald process).

3. It is extensively used in the laboratory as a cleaning agent for removing grease.

4. Ammonia is used in the refrigerators.

5. In the development of blue print of maps ammonia is used.

6. It is also used in the preparation of artificial silk.

Hydrogen Gas

Symbol: H

Molecular formula: H₂

Atomic weight: 1.008

At. No.: 1

Discovery
        Hydrogen gas was discovered by Henry Cavendish in 1776. He gave the name "inflammable gas". Later on, Lavoisier gave the name "Hydrogen". In Greek, Hydros = water & genuous = I produce.
    Hydrogen gas is found in volcanic eruptions and in petroleum substances in combination with it. All hydrocarbons have hydrogen in combination. Hydrocarbons are organic substances.

Preparation of Hydrogen Gas

         Hydrogen gas can be prepared from water, acid and alkalis.

                        Zn + 2HCL = ZnCl₂ + H₂

                        Mg + 2HCL = MgCl₂ + H₂

                        Zn + H₂SO₄ = ZnSO₄ + H₂

1.From water: Hydrogen gas can be prepared from water by electrolysis. Electrolysis is the decomposition of an electrolyte by the passage of electricity. Electrolytes are substances which in solution conduct electricity and at the same time undergo chemical decomposition. 

Fig: Electrolysis of water

     Chemical reaction is this experiment is summarized as follows:

4H₂O = 4H⁺ + 4OH^-

4H^- + 4e^- = 4H = 2H₂ (cathode)

4OH^- - 4e^- = 4OH

4OH = 2H₂O + O₂ (at anode)

During electrolysis of water, we take a voltameter as given in the figure. Water in the volameter is made electrolytic medium by adding few drops of sulphuric acid. An acidic or alkaline medium behaves as electrolytic medium. Two platinum electrodes are dipped in the water. Each electrode is connected to respective terminal of battery (cathode to negative terminal and anode to positive terminal). Two gas jars filled with water are put in as shown in the figure. When switch is on, the mechanism commences. The battery may be of 12V (DC) or 6V (DC). The overall chemical reaction is given above. Hydrogen gas is collected in cathode and oxygen gas in anode. Thus, by electrolysis, hydrogen as well as oxygen can be prepared.

Periodic Table

Introduction
         we have already discussed that elements are found in three states: solid, liquid and gas at room temperature and standard atmospheric pressure. The elements are classified according to their properties- metals and non-metals. But it is very difficult to study all the properties of all elements at the same time.

Therefore, it took long time to study the properties of elements. Finally, scientists made a table in which properties of different elements are summarized. This is called Periodic Table. Scientific Periodic table was first introduced by Mendeleeff a Russian scientist. He is known as father of Modern Periodic table. In 1869 he suggested that “there is a periodic recurrence of elements with similar chemical properties when these are written in order of increasing atomic weights”.

            Working on this principle he arranged the various elements known in the form of a table and showed that elements having similar properties fall one below the other in the same column. He was also able to predict the existence and properties of some elements unknown at that time. Although this table

best system of classification of elements. This periodic table is given above.

Periodic Table of the Elements

            Modern Periodic Table consists of seven periods and eight groups and the elements placed in the same period or group show certain regularities. In group IA, Li, Na, K, Rb, Cs and Fr are placed. The chemical properties of Na resemble to Lithium or Potassium. For example, all these three elements are soft metals. They are reactive with water. Therefore, they are called reactive elements. The characteristics of groups and period are given below:

Periods:

            A period is a horizontal row in which the elements are written until there is a recurrence of elements having similar properties. The first period consists of two elements, Hydrogen and Helium. The second and third period contain eight elements each. These are known as short periods. But fourth and fifth periods contain eighteen elements each and are known as long periods. The sixth period is again a long period and contains thirty- two elements. The seventh periods consists of six naturally occurring and thirteen recently discovered Transuranium elements (discovered by nuclear researches) and is thus, a long and incomplete period.

Characteristics of Periods:

1.Change in valency: in short periods, the valency with respects to oxygen increases from 1 to 7 while that with respect to Hydrogen rises from 1 to 4 and then falls back from 1.

2.Change in properties: elements in the same period show gradual change in their physical properties. There is a gradual change from metallic to non-metallic character and from electropositive to electronegative behavior.

3. Atomic radii: the distance from the centre of the nucleus to the outer shell is called Atomic Radius. The larger the radius the more metallic is the atom. There is progressive decrease in atomic radius from left to right.

4. Electro-negativity: it is the tendency of the atom to attract electron to itself. It is found to increase progressively from left to right.

Groups:

            These are the vertical columns. These are eight groups numbered as Group I to Group VIII. Each of the group I to VIII are further been divided into two sub-groups, i.e., the elements placed to left constituting sub-group “A” and those placed to the right constituting sub-group “B”.

Characteristics of Groups

1.Valency: The valency of the elements in any group with respect to oxygen is given by the group number.

2. Regular gradation in properties: the elements of the same sub-group show a regular gradation of physical and chemical properties with the rise of atomic weight.

Separation Of Mixture

           

Introduction

            The method of separation of impurities in liquid to obtain a pure substance is called separation of mixture. The components of mixture may be two or more than two and their separation method depends on the nature of the substances like melting points, boiling points, particle size, etc. the impurities present in water may be insoluble or soluble. They can be separated by following methods.

Method of separation of insoluble substances from a liquid:

1.      Decantation

2.      Filtration

3.      Centrifuging

Method of separation of soluble substances from a liquid:

1.      Evaporation

2.      Distillation

3.      Crystallization

4.      Chromatography

5.      Sublimation

Decantation

            The process of separation of clear liquid from the sediment (solid substance) is known as decantation. This method is applied when one component is water or liquid and the other solid (heavier than liquid).  Example, mixture of sand and water.

Filtration

            It is a process by which insoluble solid particles from a solution is separated by filter paper. For a complete and quick separation of impurities filtration process is widely used in laboratory. It is better process than sedimentation or decantation.

            The solution is carefully poured in a funnel fitted with filter paper. The pores in filter paper allow only liquid to pass through. The diameter of the pore is about 10-5 cm and the solid which cannot pass through filter paper remain in the filter paper. This is called residue. The clear liquid which we get is called filtrate.

Experiment: A mixture of sand and water is taken. With the help of a rod the solution is allowed to pass through the filter paper. The filtrate is collected in a beaker and residue remains in the filter paper.

Fig:Filtration

While pouring solution in the funnel, following precautions are to be taken.

1.The filter paper should not be torned.

2.The filter paper should be attached with the inner surface of funnel.

3.The filter paper should occupy ¾ of the funnel.

4.A glass rod should be used while transferring the liquid in the funnel.

Centrifuging

            The method of separation of solid from a solution with the help of a centrifuge, a device used for this process, is called centrifuging. This method is effective when solid substance to be separated is very less. This method is used to separate precipitate from a solution. Cream is separated from butter by this method.

Fig:Centrifuging

Experiment: in this method the solution is passed in a test tube and fitted as shown in a centrifuge. The apparatus is rotated at high speed so that the test tube also rotates. As a result the solid gets deposited at the bottom of the test tube. Then, by decantation it may be poured in the other test tube.

Evaporation 

            By this method a solvent is changed into vapour and solid is collected. The solution is heated to high temperature. When the components are miscible, this method is applied. Likewise, salt water can be separated by this method. The solute is deposited due to dehydration.

Experiment: The given mixture is taken in a evaporating dish, China dish (or in a watch glass). The dish is heated slowly so that it will not crack. Sometimes heating may be done on a steam bath. The solvent evaporates gradually and the solid remains deposited. Thus, if a solute under heating does not melt & solvent vaporizes, this method may be applied.

Fig: Evaporation

States Of Matter

Introduction

               We are living in a world where there are so many things exist. A substance exists in a state which we call state of matter. Matter has certain characteristics. The characteristic of matter is matter occupies space, has volume and weight. There is difference in properties of different types of matter and a matter may exist in a state of solid, liquid or gas.

Properties of matter

               Every matter contains certain properties. A substance which is in solid state contains the properties of solid. Besides this, it consists of the properties of the matter of which it is made. A solid substance contains molecules in compact form and the intermolecular space, the gap between two molecules, is very less. Whereas in case of liquids inter-molecular space is more. Intermolecular space is still more in gas. Whatever may be the state, matter occupies space.

               When a solid is heated, generally it turns into liquid. A liquid under heat turns into gas. This can be understood from following experiment. But, there are some substances due to heat, from solid directly turn into gas and by cooling they turn into solid. Conversion of a solid into liquid by heating is called melting or fusion. Ice melts on heating. Conversion of a solid is called solidification. When water is cooled very much, below 0C, it turns into solid.

Experiment: when a liquid is heated, generally it turns into gas. For example, steam. When water is heated it turns into vapor state which we call gaseous state. Thus, conversion of liquid into gas is called vaporization. The steam, if cooled, will turn into liquid. Thus gas may be turned into liquid. This is called condensation.

               There are some substances which turn into gaseous state when heat is given and they turn into solid under cooling. Thus, a solid when turns directly into gaseous state and converts into solid after cooling, is called sublimation. Camphor behaves like this.

Change of state

               Change of state is called the conversion from one state into other. There are different ways by which change in state takes place.

1.A solid substance which converts into liquid by heating is called fusion or melting. And such a conversion takes place at a particular temperature called melting point.

2.A liquid substance turns into vapor due to heat. Such a conversion of liquid into vapor or gaseous state is known as vaporization. For example, water converts into vapor due to heat.

3.A substance which is in vapor state, i.e., gaseous state, converts into liquid after cooling. The conversion of gas into liquid is known as liquefication or condensation. When water vapor is cooled, it turns into water again.

4.A liquid can be turned into solid after cooling very much.  Such a conversion of a liquid into solid due to cooling is known as solidification. After cooling very much, water turns into solid ice.