Describe the contact method for the manufacture of sulphuric acid under the following headings: (i) Principle of contact method (ii) Labelled diagram, its main diagram and description of the reaction.

Chemicals such as sulphuric acid are among the most important industrial chemicals in the world. Because of its industrial applications, it is called the king of chemicals. The Contact process can be used to manufacture sulphuric acid. Following are the steps involved: Preparation of sulphur dioxide. Sulphur dioxide is produced by burning sulphur or iron pyrites in excess of air. Oxidation of sulphur dioxide into sulphur trioxide. When sulphur dioxide is catalytically oxidized with atmospheric oxygen, sulphur trioxide is formed. The reaction is reversible as well as exothermic in nature. Absorption of sulphur trioxide into 98 % sulphuric acid to form oleum. Dilution of oleum with water. A suitable concentration of sulphuric acid is achieved by diluting the oleum with water in the required quantities. In the industry two steps are carried out simultaneously to make the process a continuous one and also to reduce the cost. The sulphuric acid obtained by Contact Process is 96 - 98 % pure. The following reaction will take place during the manufacturing of sulphuric acid- 2 SO 2 + O 2 → V 2 O 5 2 SO 3 SO 3 + H 2 SO 4 → H 2 S 2 O 7 H 2 S 2 O 7 + H 2 O → 2 H 2 SO 4

Give chemical equations for the reactions and the labelled diagram for the manufacture of ammonia by habers process.

On an industrial scale, ammonia is prepared by Haber’s process. The constituents of ammonia are nitrogen and hydrogen that combine in a ratio of 1 : 3 . In the Habers process, the atmospheric nitrogen is converted to ammonia by reacting it with hydrogen . Here a metal catalyst is used and high temperatures and pressures are maintained. The raw materials for the process are air, which supplies nitrogen. Natural gas and water which supply the hydrogen and the energy needed to heat the reactants. Iron which is the catalyst and does not get used up. The diagram for the preparation of ammonia is: (i) As per the diagram, in the Habers process, we take nitrogen gas from the air and combine it with hydrogen atom obtained from natural gas in the ratio 1:3 by volume. (ii) The gases are passed through four beds of catalyst, with cooling takes place in each pass. This is done to maintain equilibrium constant. (iii) While different levels of conversion occur in each pass where unreacted gases are recycled. (iv) Normally an iron catalyst is used in the process, and the whole procedure is conducted by maintaining a temperature of around 400 – 450 o C and a pressure of 150 – 200 atms. (v) The process also involves steps like shift conversion, carbon dioxide removal, steam reforming, and methanation. (vi) In the final stage of the process, the ammonia gas is cooled down to form a liquid solution which is then collected and stored in storage containers. The equation for the preparation of ammonia is: N 2 ( g ) + 3 H 2 g → 2 NH 3 g

Write formulae names and structures of five oxyacids of phosphorous.

An oxyacid can be defined as an acid that contains an oxygen atom which is bonded to the hydrogen atom and also at least one of the other elements. The five oxyacids of phosphorous are: Name Formula Structure Hypo phosphorous acid H 3 PO 2 Phosphorous acid H 3 PO 3 Phosphoric acid H 3 PO 4 Pyro phosphoric acid H 4 P 2 O 5 Meta phosphoric acid HPO 3

Explain preparation of ammonia from Habers process under following headings: (i) Diagram (ii) Method description (iii) Equation.

On an industrial scale, ammonia is prepared by Haber’s process. The constituents of ammonia are nitrogen and hydrogen that combine in a ratio of 1 : 3 . In the Habers process, the atmospheric nitrogen is converted to ammonia by reacting it with hydrogen . Here a metal catalyst is used and high temperatures and pressures are maintained. The raw materials for the process are air, which supplies nitrogen. Natural gas and water which supply the hydrogen and the energy needed to heat the reactants. Iron which is the catalyst and does not get used up. The diagram for the preparation of ammonia is: (i) As per the diagram, in the Habers process, we take nitrogen gas from the air and combine it with hydrogen atom obtained from natural gas in the ratio 1:3 by volume. (ii) The gases are passed through four beds of catalyst, with cooling takes place in each pass. This is done to maintain equilibrium constant. (iii) While different levels of conversion occur in each pass where unreacted gases are recycled. (iv) Normally an iron catalyst is used in the process, and the whole procedure is conducted by maintaining a temperature of around 400 – 450 o C and a pressure of 150 – 200 atms. (v) The process also involves steps like shift conversion, carbon dioxide removal, steam reforming, and methanation. (vi) In the final stage of the process, the ammonia gas is cooled down to form a liquid solution which is then collected and stored in storage containers. The equation for the preparation of ammonia is: N 2 ( g ) + 3 H 2 g → 2 NH 3 g

Oxygen exhibits oxidation states - 2 to + 2 while other elements of this group exhibit oxidation states + 2 , + 4 and + 6 why?

In group 16 elements the electronegativity decreases down the group with increasing atomic number. Therefore, the power to attract the electron diminishes. Thus, the tendency to show -2 oxidation state by group 16 elements decreases as the atomic number increases. Moreover, the elements other than oxygen has provisions for vacant d -orbitals in the valence shell. Apart from this, to promote the electron from 2 s - or 2 p - orbitals into 3 s - or 3 p - orbitals require large amount of energy which cannot be provided by the enthalpy of chemical reaction. Thus, elements of group 16 except oxygen can expand their octets and show higher oxidation states of +4 and +6 in their compounds. Oxygen reacts with the most electronegative element fluorine and exhibits + 1 and +2 oxidation states. Other elements of this group + 2 , + 4 , + 6 oxidation states because they are not as electronegative as oxygen.

Explain the hydrides of oxygen family under the following point : Thermal stability

With increase in the size of central atom of the hydrides of group 16 elements, the stability of X - H bond decreases. Thus, the thermal stability of the hydrides of group 16 elements decreases from oxygen to polonium. Decreasing order of stability of hydrides : H 2 O > H 2 S > H 2 Se > H 2 Te . That is, the hydride of oxygen is most stable while the hydride of tellurium is less stable because of the small size and high electronegativity of oxygen atom.

Explain the hydrides of oxygen family under the following point : Acidic property

The hydrides of group 16 elements act as weak acids and dissociate in aqueous solution to different extent giving H + ions. The acidic nature of the hydride of group 16 elements increases down the group. Water is neutral because it gives equal moles of OH 3 + and OH - ions. Hydrogen sulphide shows acidic nature in aqueous solution and ionizes as : H 2 S + H 2 O ⇌ OH 3 + + HS - HS - + H 2 O ⇌ OH - + H 2 S In the reaction between H 2 O and HS - , H 2 O donates a proton, so it exhibits the behaviour of Bronsted-Lowry acid. Increasing order of acidic strength : H 2 O < H 2 S < H 2 Se < H 2 Te

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - The p-Block Elements>Madhya Pradesh Board-2018>Q 6

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12th Madhya Pradesh Board

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Explain the hydrides of nitrogen family under the following point :

Reducing property

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