Phosphorus (P)
| Symbol | P |
| Atomic Number | 15 |
| Oxidation States | -3, +3, +5 (most common: +5 in phosphates) |
| Electronic Configuration | [Ne] 3s² 3p³ (1s² 2s² 2p⁶ 3s² 3p³) |
| Atomic Mass | 30.974 u (≈ 31 u) |
POSITION IN PREODIC TABLE
| Group | Group 15 (Nitrogen Group) |
| Periods | Period 3 |
| Block | p-block |
Ores of Phosphorus
Phosphorus (P) is a highly reactive non-metal and is never found in its free state in nature. Instead, it occurs primarily in the form of phosphate minerals in igneous and sedimentary rocks. The most important ores of phosphorus include.
Apatite Ca₅(PO₄)₃(F, Cl, OH)
Fluorapatite (Ca₅(PO₄)₃F) – Most common.
Chlorapatite (Ca₅(PO₄)₃Cl)
Hydroxyapatite (Ca₅(PO₄)₃OH) – Found in bones and teeth.
Vivianite Fe₃(PO₄)₂·8H₂O
Wavellite Al₃(PO₄)₂(OH,F)₃·5H₂O
Modern Preparation of Phosphorus (P)
Industrial Process (Electric Furnace Method)
1. Raw Material Preparation
Phosphate rock (mainly fluorapatite) is ground to a fine powder and mixed with:
- Silica (SiO2) – acts as a flux
- Coke (C) – serves as the reducing agent
Typical ratio: 5 parts phosphate rock, 3 parts silica, 1 part coke
2. Heating in Electric Arc Furnace
The mixture is heated to 1400-1500°C in an electric arc furnace.
Key points:
- Silica helps lower the melting point
- Carbon reduces phosphate to phosphorus vapor
- Calcium silicate (slag) floats on top
3. Phosphorus Collection
Phosphorus vapor (P4) is:
- Condensed under water to prevent oxidation
- Collected as white phosphorus (P4)
- Stored underwater as it’s pyrophoric
4. Purification
Crude phosphorus is purified by:
- Filtering to remove solid impurities
- Distillation at 280°C under inert atmosphere
Modern Variations
Some plants use a blast furnace variation where phosphorus is oxidized to P4O10 and then reduced.
Environmental controls are critical as the process generates CO and fluoride gases.
Phosphorus – 25 Objective Questions
1. What is the atomic number of phosphorus?
A) 13
B) 15
C) 17
D) 19
Answer: B) 15
2. Which group does phosphorus belong to in the periodic table?
A) Alkali metals
B) Halogens
C) Nitrogen group (Pnictogens)
D) Noble gases
Answer: C) Nitrogen group (Pnictogens)
3. What is the chemical symbol for phosphorus?
A) P
B) Ph
C) Ps
D) Po
Answer: A) P
4. Which of these is NOT an allotrope of phosphorus?
A) White phosphorus
B) Red phosphorus
C) Black phosphorus
D) Blue phosphorus
Answer: D) Blue phosphorus
5. Which allotrope of phosphorus is most reactive?
A) White phosphorus
B) Red phosphorus
C) Black phosphorus
D) Violet phosphorus
Answer: A) White phosphorus
6. Why is white phosphorus stored under water?
A) To prevent it from melting
B) To prevent its reaction with oxygen
C) To enhance its reactivity
D) To change its color
Answer: B) To prevent its reaction with oxygen
7. Which phosphorus allotrope is used in safety matches?
A) White phosphorus
B) Red phosphorus
C) Black phosphorus
D) Yellow phosphorus
Answer: B) Red phosphorus
8. What is the most common oxidation state of phosphorus?
A) +3
B) +5
C) -3
D) +1
Answer: B) +5
9. Which phosphorus compound is essential for bones and teeth?
A) Phosphine
B) Phosphoric acid
C) Calcium phosphate
D) Phosphorus pentoxide
Answer: C) Calcium phosphate
10. What is the formula of phosphorus pentoxide?
A) P₂O₃
B) P₂O₅
C) PO₄
D) P₄O₁₀
Answer: D) P₄O₁₀
11. Which phosphorus compound is used as a fertilizer?
A) Phosphine
B) Superphosphate
C) Phosphorus trichloride
D) White phosphorus
Answer: B) Superphosphate
12. What is the chemical formula of phosphoric acid?
A) H₃PO₃
B) H₃PO₄
C) HPO₃
D) H₄P₂O₇
Answer: B) H₃PO₄
13. Which phosphorus compound is used in detergents?
A) Sodium phosphate
B) Phosphine
C) Phosphorus pentachloride
D) White phosphorus
Answer: A) Sodium phosphate
14. What is the formula of phosphine gas?
A) PH₃
B) P₂H₄
C) P₄H₆
D) PH₄
Answer: A) PH₃
15. Which phosphorus compound is used in match heads?
A) Phosphorus trichloride
B) Phosphorus sesquisulfide
C) Phosphoric acid
D) Calcium phosphate
Answer: B) Phosphorus sesquisulfide
16. What is the nature of phosphorus pentoxide?
A) Basic oxide
B) Acidic oxide
C) Neutral oxide
D) Amphoteric oxide
Answer: B) Acidic oxide
17. Which phosphorus allotrope is thermodynamically most stable?
A) White phosphorus
B) Red phosphorus
C) Black phosphorus
D) Violet phosphorus
Answer: C) Black phosphorus
18. What is the main component of nerve gases like sarin?
A) Phosphoric acid
B) Organophosphorus compounds
C) Phosphine
D) Phosphorus pentoxide
Answer: B) Organophosphorus compounds
19. Which phosphorus compound is used in soft drinks?
A) Phosphoric acid
B) Phosphine
C) Phosphorus pentachloride
D) Calcium phosphate
Answer: A) Phosphoric acid
20. What is the shape of the phosphorus pentachloride (PCl₅) molecule?
A) Linear
B) Trigonal planar
C) Tetrahedral
D) Trigonal bipyramidal
Answer: D) Trigonal bipyramidal
21. Which phosphorus compound is used as a reducing agent?
A) Phosphoric acid
B) Hypophosphorous acid
C) Phosphorus pentoxide
D) Calcium phosphate
Answer: B) Hypophosphorous acid
22. What is the commercial method for producing phosphorus?
A) Electrolysis of phosphoric acid
B) Heating phosphate rock with coke and silica
C) Direct reaction of phosphorus with oxygen
D) Distillation of bone ash
Answer: B) Heating phosphate rock with coke and silica
23. Which phosphorus compound is used in flame retardants?
A) Phosphine
B) Ammonium phosphate
C) Phosphorus trichloride
D) White phosphorus
Answer: B) Ammonium phosphate
24. What is the biological role of phosphorus in ATP?
A) Structural component
B) Energy storage and transfer
C) Oxygen transport
D) Enzyme activation
Answer: B) Energy storage and transfer
25. Which phosphorus compound is used in smoke screens?
A) Phosphoric acid
B) White phosphorus
C) Red phosphorus
D) Calcium phosphate
Answer: B) White phosphorus