Prepare for exams with exercises on Chemical Industries, tailored to the PTB curriculum. Focus on key concepts, industrial processes, and applications to reinforce your understanding.
Short Questions (Extended Answers)
- What role is played by pine oil in the froth flotation process?
Pine oil acts as a frothing agent in the froth flotation process, which is used to separate hydrophobic materials from hydrophilic ones. It helps create a stable froth on the surface of the flotation cell, allowing valuable minerals, which are hydrophobic, to attach to air bubbles and rise to the surface for collection while the waste material (gangue) settles at the bottom. - Name the various metallurgical operations.
Metallurgical operations include:
- Crushing and grinding: Reducing the size of ore particles.
- Concentration or beneficiation: Removing impurities from the ore (e.g., froth flotation).
- Roasting and calcination: Heating ore to remove volatile impurities.
- Reduction: Extracting metals from their oxides using reducing agents.
- Refining: Purifying the extracted metal.
- How is roasting carried out?
Roasting involves heating sulfide ores in the presence of oxygen, converting them into oxides. For example, roasting zinc sulfide (ZnS) in air converts it to zinc oxide (ZnO) and sulfur dioxide (SO2). The process also helps in removing moisture and organic matter from the ore. - Explain the process of electrorefining.
Electrorefining is the purification of metals using an electrolytic cell. The impure metal is used as the anode, while a pure metal sheet serves as the cathode. When an electric current passes through the electrolyte, the pure metal dissolves from the anode and deposits onto the cathode, while impurities either dissolve in the electrolyte or form a sludge. - What are the advantages of the Solvay process?
The Solvay process, used to produce sodium carbonate (Na2CO3), has several advantages:
- Uses inexpensive and readily available raw materials (salt and limestone).
- Does not produce harmful by-products.
- The ammonia used in the process is recycled, reducing waste.
- What is the principle of the Solvay process?
The Solvay process relies on the reaction of sodium chloride (brine) with carbon dioxide and ammonia to form sodium bicarbonate, which is then heated to produce sodium carbonate. The overall reactions are designed to recycle ammonia and minimize waste. - What happens when ammoniacal brine is carbonated?
When carbon dioxide is bubbled through ammoniacal brine (a solution of ammonia and sodium chloride), sodium bicarbonate (NaHCO3) precipitates out. This occurs because sodium bicarbonate is less soluble in water, especially in the presence of ammonium chloride. - How NaHCO3 is converted to Na2CO3?
Sodium bicarbonate (NaHCO3) is heated during calcination to produce sodium carbonate (Na2CO3) and carbon dioxide (CO2). The reaction is:
2 NaHCO3 → Na2CO3 + CO2 + H2O - How is ammonia recovered in the Solvay’s process?
Ammonia is recovered by treating the solution left after sodium bicarbonate precipitation with lime (calcium hydroxide). This releases ammonia gas, which can be recycled back into the process. - How is ammonia prepared for the synthesis of urea?
Ammonia is synthesized through the Haber process, where nitrogen and hydrogen gases are reacted under high pressure and temperature in the presence of an iron catalyst to form ammonia. The produced ammonia is then used as a feedstock for urea production. - Describe the formation of petroleum.
Petroleum is formed from the remains of ancient marine organisms that settled on the ocean floor millions of years ago. Under high pressure and heat, the organic matter decomposes anaerobically, transforming into hydrocarbons over time. These hydrocarbons migrate through porous rocks and accumulate in reservoir rocks. - What is refining of petroleum, and how is it carried out?
Refining of petroleum involves separating the complex mixture of hydrocarbons into useful fractions. This is done through fractional distillation, where crude oil is heated in a distillation column, and the different components are separated based on their boiling points. - Give a use of kerosene oil.
Kerosene is used as a fuel for jet engines, in heating systems, and for lighting lamps in areas without electricity. - Describe the difference between diesel oil and fuel oil.
Diesel oil is a light distillate used primarily as fuel for diesel engines, whereas fuel oil is a heavier fraction used in industrial boilers, ships, and power plants for heating and electricity generation. - Write down the names of four fractions obtained by the fractional distillation of residual oil.
Four fractions obtained are:
- Lubricating oils
- Paraffin wax
- Asphalt
- Heavy fuel oil
- What is the difference between crude oil and residual oil?
Crude oil is the unrefined liquid extracted from the earth, containing a mixture of hydrocarbons. Residual oil is the leftover heavy fraction after the lighter hydrocarbons have been distilled off during refining. - Which petroleum fraction is used in dry cleaning?
Naphtha or light petroleum solvents are commonly used in dry cleaning due to their ability to dissolve grease and oils without damaging fabrics.
Extensive Questions (Detailed Answers)
- Describe in detail the various processes involved in the concentration of ore. Explain your answer with the help of diagrams.
Concentration of ore involves several steps to increase the metal content:
- Crushing and grinding: The ore is first broken into smaller pieces and then ground into a fine powder.
- Gravity separation: Based on density differences, heavier metal particles are separated from lighter waste.
- Froth flotation: For sulfide ores, the powdered ore is mixed with water and pine oil, then air is blown through the mixture, causing the metal-rich froth to float and be skimmed off.
- Magnetic separation: This is used for magnetic ores, where magnetic fields attract the metal particles and separate them from the non-magnetic gangue.
- Explain the process of roasting with reference to copper.
In the roasting of copper sulfide ore (e.g., Cu2S), the ore is heated in the presence of excess air. The sulfide is converted to oxide, and sulfur dioxide is released:
2Cu2S + 3 O2 → 2Cu2O} + 2 SO2.
This is followed by a reduction step to convert copper(I) oxide to metallic copper. - Write a detailed note on the Solvay process.
The Solvay process is used to manufacture sodium carbonate (soda ash). It involves the following steps:
- Ammonia absorption: Ammonia gas is absorbed in brine (sodium chloride solution).
- Carbonation: Carbon dioxide is bubbled through the ammoniacal brine, precipitating sodium bicarbonate.
- Calcination: The sodium bicarbonate is heated to form sodium carbonate.
- Ammonia recovery: The remaining solution is treated with lime to regenerate ammonia, which is recycled.
- Write a note on fractional distillation of petroleum.
Fractional distillation is a method used to separate petroleum into various components based on their boiling points. Crude oil is heated in a distillation column, and as it rises, different fractions condense at various levels, such as:
- Gasoline: Used as fuel for vehicles.
- Kerosene: Used in jet engines and heating.
- Diesel: Used in engines.
- Heavy fuel oil: Used for ships and power generation.
- How urea is manufactured? Explain with a flow sheet diagram.
Urea is manufactured by reacting ammonia and carbon dioxide under high pressure to form ammonium carbamate, which is then dehydrated to produce urea:
2 NH3 + CO2 → NH2COONH4 → NH2CONH2 + H2O
The process involves ammonia synthesis, carbon dioxide stripping, and urea synthesis sections. - How crude oil is refined? Explain two important fractions of petroleum along with their usage.
Crude oil is refined through fractional distillation. It is heated, and different components condense at different levels in the distillation column:
- Gasoline: Used as fuel for cars and motorcycles.
- Diesel oil: Used for powering heavy vehicles and machinery.
- Write a note in detail on smelting and bessemerization, giving a specific example.
- Smelting: A process where metal ores are heated to high temperatures in the presence of a reducing agent, like carbon, to extract metals. For example, iron is extracted from its ore, hematite, by smelting in a blast furnace.
- Bessemerization: It is a method of converting pig iron into steel by blowing air through the molten iron to remove impurities like carbon, silicon, and manganese. The process was crucial in
