P-BLOCK ELEMENTS

LEARNING SHEET SOLUTION -3

GXII-CHEM-p_block_elements_LSS3

Answer the following questions:

1. Define oxidation states. Ans: A number assigned to an element in chemical combination which represents the number of electrons lost (or gained, if the number is negative), by an atom of that element in the compound. OR The oxidation state, sometimes referred to as oxidation number, describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Conceptually, the oxidation state, which may be positive, negative or zero, is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component. This is never exactly true for real bonds.

2. Why does nitrogen dioxide dimerise? Ans: NO 2 contains odd number of valence electrons. That valence electron behaves as an odd electron molecule and therefore, undergoes dimerisation to form stable N 2O 4 molecule with even number of electrons.

3. What is the covalence of N in N 2O 5 ? Ans: Covalence is defined as the tendency of an atom to form number of covalent bond with other molecule.

N2O5 (Dinitrogen pentoxide) is one of the form of the nitrogen atom which belongs to group 15 in the periodic table. Nitrogen combines with oxygen to form a number of oxides having different oxidation states. Nitrogen

has tendency to form pπ-pπ multiple bonds, which decides the structure of oxides. N2O5 has following structure:

From the above structure, it is clear that Nitrogen atom is sharing its electrons with oxygen atom. Nitrogen shares it four pair of electrons with oxygen, therefore nitrogen covalency is four (4).

Answer the following questions

4. What do you understand by term oxacids? Ans: An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bond to oxygen that can dissociate to produce the H+ cation and the anion of the acid.

5. How Ostwald’s process works? Ans: The Ostwald process is a chemical process that is carried out in two stages, it converts ammonia to nitric acid (also known as HNO 3 ). In the process for step 1, ammonia is oxidized to form nitric oxide and also nitrogen dioxide. Then in step 2, the nitrogen dioxide that was formed is absorbed in water.

Watch the process click here Nitric Acid (Ostwald’s Process) Introduction On industrial process three methods are employed for the manufacture of nitric acid. Ostwald’s Process uses Ammonia as raw material. Ostwald’s Process When a mixture of ammonia and air is passed through a catalytic chamber containing electrically heated Platinum Gauze, (NO) nitric oxide is formed. This nitric oxide combines with more oxygen to form nitrogen dioxide (NO 2 ). This gas is then absorbed by water to form nitric acid. The plant used in Ostwald’s Process consist of following parts. 1. Catalytic Chamber A mixture of pure and dry ammonia is passed through a catalytic chamber containing heated (800 0C) platinum, which serves as catalyst. Here ammonia is completely oxidized to nitric oxide. 2. Oxidation Tower The nitric oxide is passed into oxidation tower where the temperature of gases falls to 200 0C – 250 0C. At this temperature nitric is oxidized to nitrogen dioxide. 2NO + O 2 —-> 2NO2 3. Absorption Tower Now the gases containing NO 2 and oxygen are than sent to a series of absorption tower, which is filled with broken quartz and water is showered from top of the tower. Then NO 2 reacts with H 2 O in the presence of oxygen to form HNO3 4NO 2 + 2H 2 O + O 2 —-> 4HNO 3

6. How concentrated nitric acid works as strong oxidizing agent? Ans: Nitric acid is strong oxidizing agent. Nitrogen in HNO 3 is in +5 oxidation state which is the highest oxidation state of nitrogen that means nitrogen cannot get oxidised but it can reduce to the lower oxidation state and oxidize other molecules or atoms in a given redox reaction.

7. Why brown ring test is performed? Ans: Brown ring test is called as nitrate test also. A nitrate test is a chemical test used to determine the presence of nitrate ion in solution.

8. What is observation of brown ring test? Ans: Brown ring test can be performed by adding Iron (II) sulphate to a solution of a nitrate then slowly adding concentrated H 2SO 4 such that it forms a layer below the aqueous solution. A brown ring will form at the junction of the two layers indicating the presence of nitrate ion. Here a sulphuric acid layer is formed under the aqueous solution

9. Write a brief note on pyrotechnics. Ans: Pyrotechnics is the science and craft of using self-contained and self-sustained exothermic chemical reactions to make heat, light, gas, smoke and/or sound. The name comes from the Greek words pyr ("fire") and tekhnikos ("made by art").[1] Pyrotechnics includes, among other things, fireworks; safety matches; oxygen candles; explosive bolts and other fasteners; parts of automotive airbags; and gas-pressure blasting in mining, quarrying, and demolition. Pyrotechnics is the science and craft of using self-contained and self-sustained exothermic chemical eactions to make heat, light, gas, smoke and/or sound. The name comes from the Greek words pyr ("fire") and tekhnikos ("made by art").[1] Pyrotechnics includes, among other things, fireworks; safety matches; oxygen candles; explosive bolts and other fasteners; parts of automotive airbags; and gas-pressure blasting in mining, quarrying, and demolition.

Pyrotechnic gerbs used in the entertainment industry

10. Define oxidizer. Ans : In chemistry, an oxidizing agent (oxidant, oxidizer) is a substance that has the ability to oxidize other substances — in other words to accept their electrons. Common oxidizing agents are oxygen, hydrogen peroxide and the halogens. In one sense, an oxidizing agent is a chemical species that undergoes a chemical reaction in which it gains one or more electrons. In that sense, it is one component in an oxidation–reduction (redox) reaction. In the second sense, an oxidizing agent is a chemical species that transfers electronegative atoms, usually oxygen, to a substrate. Combustion, many explosives, and organic redox reactions involve atom-transfer reactions.