Chemistry MCQs

Notes:
Caesium is the least electronegative element in the periodic table and Fluorine is the most electronegative. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

Notes:
Calamine is an ore that contains zinc carbonate along with impurities like iron oxide. Through smelting, the zinc carbonate in calamine can be reduced to extract pure zinc metal. Other common zinc ores are sphalerite (zinc sulfide) and smithsonite (zinc carbonate). So calamine is considered a zinc ore due to its zinc carbonate content.

Notes:
Gobar Gas or Biogas is mostly methane (CH₄) and carbon dioxide (CO₂) and may have small amounts of hydrogen sulfide (H₂S), moisture and siloxanes.

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Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperatures (<283 k) and shows high water absorption capacity. It is soluble in non-polar solvents and is non-resistant to attack by oxidising agents. To improve upon these physical properties, a process of vulcanisation is carried out. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 K. On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.
 In the manufacture of tyre rubber, 5% of sulphur is used as a crosslinking agent

Notes:
Platinum is a naturally white metal. It doses not need to be alloyed for color. Due to its appearance as white, it is commonly known as White Gold.

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Nitrous oxide is often referred to as “Laughing Gas” due to the euphoric effect it produces when inhaled. Its chemical formula is N2O and it is an oxide of nitrogen. At room temperature, it is a colorless, non-flammable gas with a relatively sweet odor and taste. It is primarily used in dentistry and surgery for its analgesic and anesthetic properties. It is also noted for its role as a major greenhouse gas and air pollutant, as well as a natural regulator of stratospheric ozone.

Notes:
Diamond and graphite are both forms of carbon but they exhibit different properties due to variations in their bonding arrangements. Diamond does not conduct electricity as each carbon atom in diamond is covalently bonded to four other carbon atoms, leaving no free electrons to conduct electricity. On the other hand, graphite is a good conductor of electricity due to its layered structure which leaves free electrons between the layers.

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:
Chile saltpetre, or sodium nitrate (NaNO3), differs from regular saltpetre, which typically refers to potassium nitrate (KNO3). Chile saltpetre is primarily composed of sodium, while traditional saltpetre contains potassium. Historically, Chile saltpetre was extensively mined in the Atacama Desert and was crucial for fertilizer and explosives in the 19th century.

Notes:
Isobutane, which is known in the industry as R600A has been used in several domestic refrigerators in recent times because it is an excellent refrigerant and non-ozone depleting substance with low global warming potential. The only drawback is that it is highly inflammable.