Chemistry MCQs

Notes:
Bakelite is a thermosetting plastic formed from phenol and formaldehyde, used in electrical insulators and cookware handles. Unlike thermoplastics, it hardens irreversibly when heated and cannot be remolded. It was the first synthetic plastic, invented by Leo Baekeland in 1907.

Notes:
Hydrogen (H2) gas is utilized in the manufacture of Vanaspati ghee from vegetable oils. The process involves hydrogenation, a chemical reaction between molecular hydrogen (H2) and another compound or element. Hydrogenation of vegetable oils helps to convert them into a semisolid form that resembles ghee, often used as a cheaper alternative to butter or ghee in cooking.

Notes:
Nitrolim is a type of fertilizer that was widely used in the past. The main components of Nitrolim are calcium carbide and nitrogen. Calcium carbide reacts with nitrogen to form calcium cyanamide, which is an active ingredient in Nitrolim. This fertilizer is significant as it helps in fixing nitrogen in the soil thereby promoting plant growth.

Notes:
Vapor pressure of water increases as its temperature rises. At 25°C, water’s vapor pressure is approximately 23.8 mmHg, while at 100°C it reaches 760 mmHg. When a liquid is heated, kinetic energy of molecules grows, allowing more to escape as vapor and thus increasing vapor pressure.

Notes:
The auto-ignition temperature of a liquid, gas or vapor is the temperature at which the substance will ignite without any external heat source. Here is the temperature of some gases: 
Methane -580 °C 
Hydrogen -560 °C 
Propane -493 °C 
Ethylene -425 °C 
Acetylene -305 °C 
Naphtha -290 °C 
Carbon disulfide -102 °C

Notes:
The correct answer is Hydrochloric Acid. When testing for adulteration of pure ghee with vanaspati or margarine, hydrochloric acid is used because it reacts with the fats present in these substances, producing a distinct color change. This method is based on the principle that the presence of unsaturated fats in vanaspati or margarine will lead to a different reaction compared to pure ghee. Hydrochloric acid is commonly used in food testing due to its effectiveness in identifying such adulterants.

Notes:
Gun metal is an alloy primarily composed of copper, tin, and zinc. Specifically, it typically contains about 88% copper, 10% tin, and 2% zinc. This alloy is known for its strength, corrosion resistance, and ability to withstand high temperatures, making it ideal for manufacturing firearms and artillery. The term “gun metal” dates back to the 15th century when it was used for cannons and other weaponry.

Notes:
When sulfuric, and nitric acids, present in the acid rain reacts with the calcite in marble and limestone, it get dissolve and formed gypsum and washed off by the water. The rain can dissolve limestone and marble through direct contact.

Notes:
Sodium bicarbonate, commonly known as baking soda, is used in baking due to its ability to decompose above 70 degrees Celsius and release carbon dioxide. This chemical reaction is given by the equation 2 NaHCO3 – Na2CO3 + H2O + CO2. In baking, it reacts with other ingredients or decomposes at high temperatures to produce carbon dioxide, which causes the dough to rise, creating the fluffy texture in baked goods.

Notes:
The first synthetic plastic was actually celluloid, invented by Alexander Parkes in 1855. Initially, celluloid was primarily used in photographic films. However, it had limitations, not suitable for making containers or electrical insulation. The first genuine plastic, Bakelite, was invented by Leo Baekeland in 1909 and extensively used in various applications, including safely handled autos. World War I significantly contributed to the development of polystyrene and polyvinyl chloride, widely used in plumbing and electrical insulation. Later, in the 1930s, nylon was invented, and by 1950, plastic materials gained immense popularity.