Chemistry GK Questions Quiz-10

Chemistry GK Questions Quiz-10

Chemistry Multiple Choice Questions (MCQs) Quiz for State and UPSC Civil Services Examinations. Objective Questions on Chemistry for competitive examinations.

    181. Percentage of lead in lead pencils is

    (1) 0 
    (2) 31-66
    (3) 40 
    (4) 80
    Answer:
    181. (1) There is no lead in pencils. Rather, the core is made up of non-toxic mineral called graphite. The common name “pencil lead” is due to an historic association with the stylus made of lead in ancient
    Roman times. Most pencil cores are made of graphite mixed with a clay binder, leaving grey or black marks that can be easily erased. Graphite pencils are used for both writing and drawing, and the result is durable: although writing can usually be removed with an eraser, it is resistant to moisture, most chemicals, ultraviolet radiation and natural aging. Other types of pencil core are less widely used. Charcoal pencils are mainly used by artists for drawing and sketching. Coloured pencils are sometimes used by teachers or editors to correct submitted texts but are more usually regarded as art supplies, especially those with waxy core binders that tend to smear on paper instead of erasing. Grease pencils have a softer crayon-like waxy core that can leave marks on smooth surfaces such as glass or porcelain.

    182. Water is not effective in extinguishing a fire caused by petrol because

    (1) the flame is too hot for water to cool it down
    (2) water and petrol react chemically
    (3) water and petrol are miscible with each other
    (4) water and petrol are immiscible with each other and petrol which forms the upper layer continues to burn
    Answer:
    182. (4) Water is not effective in extinguishing a fire caused by petrol because water and petrol are immiscible with each other and petrol which forms the upper layer continues to burn. The specific gravity (or relative density) of gasoline ranges from 0.71–0.77 kg/l (719.7 kg/m3) while the specific gravity of water is 1000 kg/m3 and that is why gasoline or petrol floats on the upper surface of the water. Water cannot generally be used to extinguish a gasoline fire, unless used in a fine mist.

    183. Helium gas is used in gas balloons instead of hydrogen gas because it is

    (1) lighter than hydrogen
    (2) more abundant than hydrogen
    (3) non-combustible
    (4) more stable
    Answer:
    183. (3) Because of the Archimedes’ principle, a lifting gas is required for aerostats to create buoyancy. Its density is lower than that of air (about 1.29 kg/m3, 1.29 g/ L). Only certain lighter than air gases are suitable as lifting gases. Hydrogen and helium are the most commonly used lift gases. Although helium is twice as heavy as (diatomic) hydrogen, they are both so much lighter than air that this difference is
    inconsequential. Both provide about 9.8 N of lift (1 Newton is the force required to accelerate 1 kg at 1
    m/sec2) per cubic meter of gas at STP. Helium is the second lightest gas. For that reason, it is an attractive gas for lifting as well. A major advantage is that this gas is noncombustible. Today helium is used instead of hydrogen, since it is inert so non-flammable which makes things a lot safer. Hydrogen can ignite very easily when mixed with the oxygen of the surrounding air.

    184. The gas used in the artificial ripening of fruits is

    (1) Acetylene 
    (2) Methane
    (3) Ethane 
    (4) Butane
    Answer:
    184. (1) Ripening is a process in fruits that causes them to become more palatable. In general, a fruit becomes sweeter, less green, and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity level does not make the fruit seem tarter, which can lead to the misunderstanding that the riper the fruit the sweeter. Ripening agents speed up the ripening process. They allow many fruits to be picked prior to full ripening, which is useful, since ripened fruits do not ship well. For example, bananas are picked when green and artificially ripened after shipment by being gassed with ethylene. Calcium carbide is also used for ripening fruit artificially in some countries. Calcium carbide reacts with water to produce acetylene, which acts as an artificial ripening agent. Industrial-grade calcium carbide may contain traces of arsenic and phosphorus which makes it a human health concern. The use of this chemical for this purpose is illegal in most countries.

    185. Ruby and sapphire are oxides of

    (1) copper 
    (2) tin
    (3) iron 
    (4) aluminium
    Answer:
    185. (4) Aluminium forms one stable oxide, known by its mineral name corundum. Sapphire and ruby are impure corundum contaminated with trace amounts of other metals. Corundum is a crystalline form of aluminium oxide (Al2O3) with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colours when impurities are present. Transparent specimens are used as gems, called ruby if red and padparadscha if pink-orange. All other colours are called sapphire, e.g., “green sapphire” for a green specimen. Because of corundum’s hardness (pure corundum is defined to have 9.0 Mohs), it can scratch almost every other mineral. It is commonly used as an abrasive, on everything from sandpaper to large machines used in machining metals, plastics, and wood. Some emery is a mix of corundum and other substances, and the mix is less abrasive, with an average hardness near 8.0.

    186. The gas which turns into liquid at the lowest temperature among the following is

    (1) hydrogen 
    (2) oxygen
    (3) helium 
    (4) nitrogen
    Answer:
    186. (1) Liquid hydrogen (LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below hydrogen’s critical point of 33 K. However, for hydrogen to be in a full liquid state without evaporating at atmospheric pressure, it needs to be cooled to 20.28 K (-423.17 °F/-252.87°C). One common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is typically used as a concentrated form of hydrogen storage.

    187. Gunpowder consits of a mixture of

    (1) sand and TNT
    (2) TNT and charcoal
    (3) nitre, sulphur and charcoal
    (4) sulphur, sand and charcoal
    Answer:
    187. (3) Gunpowder, also known since the late 19th century as black powder, was the first chemical explosive and the only one known until the mid-1800s. It is a mixture of sulfur, charcoal, and potassium nitrate (saltpetre)— with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer. Because of its burning properties and the amount of heat and gas volume that it generates, gunpowder has been widely used as a propellant in firearms and as a pyrotechnic composition in fireworks. Gunpowder is classified as a low explosive because of its relatively slow decomposition rate and consequently low brisance. Low explosives deflagrate at subsonic speeds, whereas high explosives detonate, producing a supersonic wave. Ignition of the powder packed behind a bullet must generate enough pressure to force it from the muzzle at high speed, but not enough to rupture the gun barrel. Gunpowder is thus less suitable for shattering rock or fortifications.

    188. In nuclear reactors, graphite is used as a/an

    (1) fuel 
    (2) lubricant
    (3) moderator
    (4) insulator
    Answer:
    188. (3) A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid (water or gas), which runs through turbines that power either ship’s propellers or generators. Some produce isotopes for medical and industrial use, and some are run only for research. In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235. Commonly used moderators include regular (light) water (roughly 75% of the world’s reactors), solid graphite (20% of reactors) and heavy water (5% of reactors). Beryllium has also been used in some experimental types, and hydrocarbons have been suggested as another possibility.

    189. Sea water can be purified by the process of

    (1) distillation
    (2) evaporation
    (3) filtration
    (4) fractional distillation
    Answer:
    189. (1) The traditional process used in desalination operations is vacuum distillation—essentially the
    boiling of water at less than atmospheric pressure and thus a much lower temperature than normal. This
    is because the boiling of a liquid occurs when the vapor pressure equals the ambient pressure and vapor
    pressure increases with temperature. Thus, because of the reduced temperature, energy is saved. Multistage flash distillation, a leading method, accounted for 85% of production worldwide in 2004.
    Vacuum distillation is a method of distillation whereby the pressure above the liquid mixture to be distilled is reduced to less than its vapor pressure (usually less than atmospheric pressure) causing evaporation of the most volatile liquid(s) (those with the lowest boiling points). This distillation method works on the principle that boiling occurs when the vapor pressure of a liquid exceeds the ambient pressure. Vacuum distillation is used with or without heating the mixture.

    190. Detergents clean surfaces on the principle of

    (1) viscosity
    (2) surface tension
    (3) elasticity
    (4) floatation
    Answer:
    190. (2) Detergents and soaps are used for cleaning because pure water can’t remove oily, organic soiling. Soap cleans by acting as an emulsifier. Basically, soap allows oil and water to mix so that oily grime can be removed during rinsing. Detergents were developed in response to the shortage of the animal and vegetable fats used to make soap during World War I and World War II. Detergents are primarily surfactants, which could be produced easily from petrochemicals. Surfactants lower the surface tension of water, essentially making it ‘wetter’ so that it is less likely to stick to itself and more likely to interact with oil and grease. Modern detergents contain more than surfactants. Cleaning products may also contain enzymes to degrade protein-based stains, bleaches to de-colour stains and add power to cleaning agents, and blue dyes to counter yellowing. Like soaps, detergents have hydrophobic or water-hating molecular chains and hydrophilic or water-loving components.

    191. The compound to which H2 does not add is

    (1) Biphenyl ethylene
    (2) Tetraphenyl ethylene
    (3) Tetra – a –naphthylethylene
    (4) Tetra –9 – phenanthrylethylene
    Answer:
    191. (2) While H2 is not very reactive under standard conditions, it does form compounds with most
    elements. Millions of hydrocarbons are known, but they are not formed by the direct reaction of
    elementary hydrogen and carbon. Hydrogen can form compounds with elements that are more electronegative, such as halogens. Hydrogen forms a vast array of compounds with carbon. Tetraphenylethylene is a chemical compound that can be used in construction and n the manufacture of
    medical equipment, packaging, and electrical appliances. Tetraphenylethylene can be synthesized from diphenyldichloromethane.

    192. Ammonial is a mixture of

    (1) aluminium powder and ammonium nitrate
    (2) aluminium powder and ammonium chloride
    (3) aluminium powder and ammonium sulphate
    (4) aluminium powder and potassium nitrate
    Answer:
    192. (1) Ammonal is an explosive made up of ammonium nitrate and aluminium powder. The ammonium nitrate functions as an oxidizer and the aluminium as fuel. The use of the relatively cheap ammonium nitrate and aluminium makes it a replacement for pure TNT. The mixture is affected by humidity because ammonium nitrate is highly hygroscopic. Ammonal is not easily detonated, requiring a fairly substantial shock, though it is still more sensitive than trinitrotoluene and composition C4 . The detonation velocity of ammonal is approximately 4,400 metres per second or 9,842 miles per hour. Ammonal used for military mining purposes was generally contained within metal cans or rubberised bags to prevent moisture ingress problems. The composition of ammonal used at Messines was 65% ammonium nitrate, 17% aluminum, 15% trinitrotoluene (TNT) and 3% charcoal. Ammonal remains in use as an industrial explosive. Typically, it is used for quarrying or mining purposes.

    193. Which gas does not form the part of atmosphere ?

    (1) Nitrogen 
    (2) Helium
    (3) Chlorine
    (4) None of the above
    Answer:
    193. (3) The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth’s gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variations). Air is the name given to the atmosphere used in breathing and photosynthesis. Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%. While air content and atmospheric pressure vary at different layers, air suitable for the survival of terrestrial plants and terrestrial animals is currently only known to be found in Earth’s troposphere and artificial atmospheres. Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the major gases of the atmosphere. The remaining gases are often referred to as trace gases, among which are the greenhouse gases such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds.

    194. The fuel used in an atomic reactor is

    (1) Coal
    (2) Petrol
    (3) Combustable gases
    (4) Uranium
    Answer:
    194. (4) A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid (water or gas), which runs through turbines that power either ship’s propellers or generators. Some produce isotopes for medical and industrial use, and some are run only for research. When a large fissile atomic nucleus such as uranium-235 or plutonium-239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or lighter nuclei (the fission products), releasing kinetic energy, gamma radiation and free neutrons. A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This is known as a nuclear chain reaction.

    195. White coal is

    (1) Uranium
    (2) Hydro-electricity
    (3) Diamond
    (4) Ice
    Answer:
    195. (*) White coal is a form of fuel produced by drying chopped wood over a fire. It differs from charcoal which is carbonised wood. White coal was used in England to smelt lead ore from the mid-sixteenth to the late seventeenth centuries. It produces more heat than green wood but less than charcoal and thus prevents the lead evaporating. White coal could be use mixed with charcoal for other industrial uses than lead smelting. White coal was produced in distinctive circular pits with a channel, known as Q-pits. They are frequently found in the woods of South Yorkshire.

    196. The major constituent of gobar gas is

    (1) Carbon dioxide
    (2) Methane
    (3) Butane
    (4) Isobutane
    Answer:
    196. (2) Gobar Gas (Methane) is generated by the decomposition of organic cow dung. It consists of 55-65% methane, 30-35% carbon dioxide, with some hydrogen, nitrogen and other traces. The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55– 75% methane, which for reactors with free liquids can be increased to 80-90% methane using in-situ gas purification techniques. As-produced, biogas also contains water vapor. The fractional volume of water vapor is a function of biogas temperature; correction of measured gas volume for both water vapor content and thermal expansion is easily done via a simple mathematic algorithm which yields the standardized volume of dry biogas.

    197. The residue left after extracting juice from sugarbeet and sugarcane is called

    (1) molasses 
    (2) bagasse
    (3) whey 
    (4) biomass
    Answer:
    197. (2) Bagasse is the fibrous matter that remains after sugarcane or sorghum stalks are crushed to extract their juice. It is currently used as a biofuel and in the manufacture of pulp and paper products and building materials. Agave bagasse is a similar material that consists of the tissue of the blue agave after extraction of the sap. For each 10 tonnes of sugarcane crushed, a sugar factory produces nearly 3 tonnes of wet bagasse. Since bagasse is a by-product of the cane sugar industry, the quantity of production in each country is in line with the quantity of sugarcane produced. The high moisture content of bagasse, typically 40 to 50%, is detrimental to its use as a fuel. In general, bagasse is stored prior to further processing. For electricity production, it is stored under moist conditions, and the mild exothermic reaction that results from the degradation of residual sugars dries the bagasse pile slightly.

    198. The isotope of Uranium used in atomic reactors is

    (1) U235 
    (2) U236
    (3) U237 
    (4) U232
    Answer:
    198. (1) A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid (water or gas), which runs through turbines that power either ship’s propellers or generators. Some produce isotopes for medical and industrial use, and some are run only for research. When a large fissile atomic nucleus such as U235 or U239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or lighter nuclei (the fission products), releasing kinetic energy, gamma radiation and free neutrons. A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This is known as a nuclear chain reaction.

    199. Which one of the following is not a radio-active element ?

    (1) Uranium 
    (2) Thorium
    (3) Radium 
    (4) Cadmium
    Answer:
    199. (4) Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. Because the nucleus experiences the intense conflict between the two strongest forces in nature, it should not be surprising that there are many nuclear isotopes which are unstable and emit some kind of radiation. The most common types of radiation are called alpha, beta, and gamma radiation, but there are several other varieties of radioactive decay. Among uranium, thorium, radium and cadmium the first three does show radioactive properties while the fourth one does not show any kind of radioactive properties.

    200. The greenhouse effect is caused by the higher level of which gas in the atmosphere ?

    (1) Carbon monoxide
    (2) Carbon dioxide
    (3) Nitrous oxide
    (4) Sulphur dioxide
    Answer:
    200. (2) The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases. The environmental effects of carbon dioxide are of significant interest. In the earth’s atmosphere, it acts as a greenhouse gas which plays a major role in global warming and anthropogenic climate change. Also a major source of ocean
    acidification is CO2 which dissolves in water forming carbonic acid, which is a weak acid, because CO2 molecule ionization in water is incomplete.


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