Phosphorus

Give scientific reasons: 1. Yellow phosphorus is never found in Free State. Ans. Yellow phosphorus is never fund in Free State because 1. It is highly reactive, as in yellow phosphorus, the P4 molecules are loosely held together by weak forces and hence it is very easy for phosphorus to react with any other element. 2. Yellow phosphorus shows phosphorescence. Ans. 1. Yellow phosphorus when exposed to air undergoes slow oxidation. 2. In this reaction, light is produced. Due to this light, yellow phosphorus glows when it kept in the dark. 3. This property is called phosphorescence. Hence, yellow phosphorus shows phosphorescence. 3. Match stick does not burn in cold flame. Ans. Match stick does not burn in cold flame because. 1. The temperature of the clod flame is very low, much below even the boiling point of water. 2. So, if a match stick is held in it, it will not catch fire. 4. Yellow Phosphorus is kept under water. Ans. 1. Yellow phosphorus has low ignition temperature of 300 C and catches fire even at room temperature. 2. It readily combines with oxygen at room temperature to form phosphorus pentoxide. 3. It is heavier than water, does not react with water and does not dissolve in it. Hence, yellow phosphorus is kept under water. 5. It is dangerous to handle yellow phosphorus. Ans. 1. It is dangerous to handle yellow phosphorus because the ignition temperature of yellow phosphorus is 300 C. 2. While our normal body temperature is 370 C, hence when it comes in contact with the body, it causes painful wounds. 6. Red phosphorus is kept in airtight bottles. Ans. 1. Red phosphorus is hygroscopic. 2. If it is kept exposed to air, it absorbs the moisture in air and becomes wet. Hence, red phosphorus is kept in airtight bottles. 7. Yellow phosphorus is used in war technique.

Ans. 1. Yellow phosphorus readily combines with oxygen at room temperature to form phosphorus pentoxide. 2. Phosphorus pentoxide (P2O5) forms dense white fumes so it can form an effective smoke screen. 3. Hence yellow phosphorus is used in war technique. i.e. in the manufacture of smoke bombs and fireworks. 8. Yellow phosphorus is more reactive than red phosphorus. Ans. 1. A chemical reaction is breaking of bonds of molecules and formation of new bonds. 2. In yellow phosphorus, the P4 molecules are loosely held together by weak bonds and hence it is more reactive. 3. On the other hand, the P4 molecules of red phosphorus are held together by stronger bonds and hence it is less reactive. 9. Bones of dead animals are often used to extract phosphorus. Ans. 1. Bones of animals contain about 60% of calcium phosphate. 2. A considerable amount of phosphorus can be extracted from them by simple process. Hence, bones of dead animals are often used to extract phosphorus. 10. In rainy season the surface of the match box on which matchstick is rubbed becomes damp. Ans. One of the components on the safety matches is red phosphorus Red phosphorus is a hygroscopic substance. It absorbs moisture from atmosphere and gets damp. Hence safety matches get damp (moist) in rainy season.

II. Answer the following in short.

IV. Answer the following briefly; 1. Distinguish between yellow phosphorus and red phosphorus. Yellow Phosphorus Red Phosphorus. 1. It is outwardly yellow inwardly 1. It is reddish brown in colour. white. 2. Melting point is 440 C under 2. Melting point is 5900 C under water. pressure. 3. It is poisonous. 3. It is non - Poisonous. 4. Ignition temperature is 300 C 4. Ignition temperature is 2600 C. 5. It has garlic odour. 5. It is odourless 6. It is not used in safety matches 6. It is used in safety matches 7. It is soluble in carbon disulphide. 7. Insoluble in carbon disulphide. 8. Reacts with sodium hydroxide to 8. No reaction with sodium give phosphine gas. hydroxide. 9. Density of yellow phosphorus = 1.8 gm / cm 3 9. Density of Red phosphorus = 2.35 gm/cm 3

III. Write short notes on Cold flame:

Take some water in hard glass test tube. Introduce a few pieces of yellow phosphorus into it. Fit the mouth of the test tube with a rubber stopper. Fit a glass tube with a small jet into the stopper. Make the room dark and gently heat the test tube. Phosphorus vaporizes as a result of heat. Vapours of phosphorus begin to be slowly oxidised in air and flame appears at the nozzle known as cold flame. Hold a matchstick in the flame. It does not catch fire. IV Answer the followings 1. What are the allotropes of phosphorus? Explain molecular structure of allotropes. Ans. Phosphorus exhibits two main allotropic forms yellow phosphorus and red phosphorus. 1. Molecular structure of yellow phosphorus: - The molecule of yellow phosphorus is tetrahedron. In solid yellow phosphorus, these P4 molecules are loosely held together by weak forces.

2. Molecular structure of red phosphorus: - Its structure is different from yellow phosphorus. In yellow phosphorus, the molecules are loosely held but in red

phosphorus, they are strongly held by covalent bond. Red phosphorus is a covalent crystal lattice consisting of infinite chains of phosphorus atoms. Hence, it is less reactive than yellow phosphorus.

2. Explain with a labeled diagram the extraction of phosphorus from bone ash (Phosphorite). Ans.

1. A mixture of calcium phosphate (bone ash) and silica (Sand) and coke id heated in

2. 3. 4. 5.

6.

a electric furnace at a temperature of 14000 To 15000 C. Calcium phosphate first reacts with sand (Silica) to form calcium silicate and Vapours of phosphorus pent oxide. Phosphorus pent oxide is then reduced by coke to form vapors of phosphorus and carbon monoxide. Calcium silicate is collected at the bottom in the form of slag. Vapours of phosphorus and carbon monoxide are made to pass through the water. Carbon monoxide being insoluble in water escapes out and Vapours of phosphorus condenses into solid. Phosphorus is further purified by melting under water and by treatment with potassium dichromate and dilute sulphuric acid.

Q1. Define 1. Allotropy: - The phenomenon of existence of two or more forms of an element which exhibit different physical properties but have same chemical properties is called allotropy. Eg. Yellow phosphorus and red phosphorus are allotropes of phosphorus. Carbon also exhibits allotropy. 2. Phosphorescence: - The phenomenon of glowing of a substance in the dark is called phosphorescence. Eg. Yellow phosphorus glows in the dark because it vaporises slowly and the vapours get slowly oxidised forming greenish yellow flame. 3. Give the following of phosphorus: Valency: - Valency of phosphorus is 3 and 5. Molecular formula: - Molecular formula of phosphorus is P4. Q2. Answer the following in short. 1. Give the names of mineral of phosphorus. Ans.

2. Explain the position of phosphorus in the periodic table and its electronic configuration. Ans. 1. The atomic number of phosphorus is 15. So, its electronic configuration is 2,8,5. 2. Phosphorus contains five electrons in its outermost shell. Hence it is place in group Vth of the periodic table. 3. Also, being a normal element, it is placed in Vth A group, below nitrogen. 4. Since, it contains three shells; it is placed in the third period. 3. How is phosphorus useful for our body? Ans. 1. Animal (including ourselves) bones contain about 60% of calcium phosphate. Phosphorus is also present in different parts of animal body. i.e. teeth, brain, muscles, blood etc. in the form of phosphates. 2. Phosphorus is an important constituent of the DNA molecule. It is present in the form of phosphoric acid. Linearly arranged segments of DNA are called Genes which in turn are present in the chromosomes. 3. Genes control cellular activities and deal with transmission and expression of hereditary factors. 4. Thus phosphorus is essential for the proper growth and development of animals. 4. Who discovered phosphorus and why named it as phosphorus? Ans. Phosphorus was discovered by German Chemist Brandt in 1669. It was named as phosphorus because it glows in the dark ('Phos' means light and 'Phero' means I carry.)

5. What is the principle ore of Phosphorus? What are the chemicals mixed with this ore to extract phosphorus? Ans. The principle ore of phosphorus is phosphorite or bone ash; the chemicals mixed with this ore to extract phosphorus are sand (silica) and coke. 6. What is the role of sand and coke in the extraction of Phosphorus? Ans. 1. During extraction of phosphorus from bone ash or phosphorite, sand react with calcium phosphate from the ore to give calcium silicate (slag) and phosphorus pentoxide. 2. The calcium silicate, thus obtained, is collected at the bottom in the form of fusible slag and phosphorus pentoxide is released. 3. Phosphorus pentoxide, formed by the reaction of silica with calcium phosphate is reduced to phosphorus by coke. 4. Here, Coke, a form of carbon acts as a reducing agent in the process of extraction of phosphorus. 7. How yellow phosphorus is stored in laboratory? Why? Ans. 1. Yellow phosphorus is stored under water in laboratory. This is because yellow phosphorus readily combines with oxygen at room temperature to form phosphorus pentoxide. Since its ignition temperature is low (300C). 2. It also catches fire because of the heat liberated during oxidation. 3. Moreover, yellow phosphorus is insoluble in water and also heavier than water (density of yellow phosphorus = 1.8gm/cm3and that of water = 1.0 gm/cm3). 4. Hence to prevent yellow phosphorus from coming into contact with atmospheric oxygen, it is stored under water. 8. Give any four chemical properties of yellow phosphorus. Ans. 1. When yellow phosphorus is exposed to air at room temperature, it undergoes oxidation to form phosphorus pentoxide. 2. When yellow phosphorus is held in a gas jar containing chlorine, it spontaneously combines with chlorine forming a mixture of phosphorus trichloride and phosphorus pentachloride. 3. When yellow phosphorus is heated with a concentrated solution of potassium hydroxide, potassium hypophosphite is formed and phosphine gas is evolved. 4. Yellow phosphorus glows in the dark. 9. Give any two chemical properties of red phosphorus. Ans. 1. When red phosphorus is heated with chlorine, a mixture of phosphorus trichloride and phosphorus pentachloride is formed. 2. When red phosphor is burnt in air, it undergoes oxidation to form phosphorus pentoxide. 10. How is phosphorus purified? (OR) Write a short note on refining of phosphorus. Ans. 1. The crude yellow phosphorus obtained from the furnace is purified by melting it under water then treating it with a mixture of potassium dichromate and dilute sulphuric acid.

2. The impurities get oxidised, but phosphorus remains unaffected. 3. Yellow phosphorus is purified in this way. 11. Give uses of phosphorus. Ans. The important uses of phosphorus are 1. It is used in match industry. 2. It is used for making hard and none rusting alloy phosphor bronze. 3. It is used in the manufacture of smoke bombs, fie works etc. 4. It is used in the preparation of zinc phosphide, which is used as a rat poison. 5. It is used in the preparation of phosphate fertilizers. 12. Give the physical properties of red phosphorus. Ans. Physical properties of red phosphorus are 1. It is reddish brown solid. 2. It is amorphous. 3. Its density is 2.35 g/cm3. 4. It is odourless, non – poisonous and hygroscopic solid. 5. It is insoluble in water as well as in carbon disulphide. 6. Its ignition temperature is 2600 C and it melts at 5900 C, under pressure. 13. Give the physical properties of yellow phosphorus. Ans. Physical properties of yellow phosphorus are 1. It is a soft wax like solid substance, which can be cut with a knife. 2. Its density is 1.8 g/cm3. 3. It is white when pure, but becomes pale yellow when exposed to light. 4. It smells like garlic. 5. It is insoluble in water but soluble in organic solvent like carbon disulphide, chloroform, benzene etc. 6. It ignites at 300 C in air and it melts at 440 C under water. 7. It is poisonous. (Its vapour causes a disease named (phossy – jaw)