Chemistry MCQs

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Sulphur is a non-metal that shows allotropy in the liquid state. If sulphur is heated slowly the changes between the different forms can be observed. These changes are in the form of colour and viscosity (thickness) of the liquid. If the dark brown liquid sulphur is poured into a beaker of cold water, plastic sulphur is formed. This is an elastic, rubber-like form of sulphur. The tow commonly know allotropic forms of sulphur are monoclinic and rhombhic sulphur.

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In arc welding, Argon is used as a shielding gas because it is chemically inert and forms no compounds. At the high temperatures that welding requires, the metals being welded become highly reactive to the elements in the atmosphere. Contamination from these elements can lead to brittle welds and instability in the welding arc. So,argon and other inert gases are sprayed.

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Sulphur (as sulphate) is a major plant nutrient, and is essential for crop growth. Calcium Sulphate (gypsum) is used to improve soil quality. Calcium sulphate acts as a pH buffer, which can contribute to neutralizing both soil alkalinity and acidity. It is mainly used for the reclamation of sodic soils through ion exchange (calcium replacing sodium).

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White phosphorus is the most reactive form of phosphorus. It is made up of discrete P4 tetrahedra which are subjected to very high angular strain as the angles is 60 degrees. This high angular strain makes white phosphorus unstable and highly reactive. It ignites spontaneously at about 50°C, and at much lower temperatures if finely divided. Therefore, it is stored in cold water in brown coloured bottles.

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Phosphorus (P) is a non-metal that sits just below nitrogen in group 15 of the periodic table. This element exists in several forms, of which white and red are the best known. Other than a few exceptions, minerals containing phosphorus are in the maximally oxidized state as inorganic phosphate rocks.

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Hydrogen sulfide (H2S) is a colourless gas with a characteristic odour of rotten eggs. It is often produced from the microbial breakdown of organic matter in the absence of oxygen gas, such as in swamps and sewers; this process is commonly known as anaerobic digestion.

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Quartz sand (silica), lime (calcium oxide) along with magnesium oxide (MgO) and aluminium oxide (Al2O3) are used to produce good quality glass. The glass containing about 70 to 74% silica by weight and is called a soda-lime glass. It accounts for about 90% of manufactured glass.

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Silica gel is a drying agent, meant to remove moisture from an enclosed space. It is a granular, vitreous, porous form of silicon dioxide made synthetically from sodium silicate.Silica gel packs are found in boxes containing electronics or new shoes and inside purses or medicine bottles. The packets contain either granular silicic acid, which resembles sand, or tiny gel beads.

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Many chemical reactions release energy in the form of heat, light, or sound. These are exothermic reactions. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. Some examples of exothermic reactions are: burning of natural gas; respiration, nuclear fission and the decomposition of vegetable matter into compost.

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Under 1% of the uranium found in nature is the easily fissionable U-235 isotope and as a result most reactor designs require enriched fuel. Enrichment involves increasing the percentage of U-235 and is usually done by means of gaseous diffusion or gas centrifuge. The enriched result is then converted into uranium dioxide powder, which is pressed and fired into pellet form. These pellets are stacked into tubes which are then sealed and called fuel rods. Most BWR and PWR commercial reactors use uranium enriched to about 4%.