Chemistry MCQs

Notes:
Plaster of Paris is calcium sulphate hemihydrate. The formula is given as, CaSO4.1/2 H2O or (2 CaSO4) . H2O. The powder is called plaster of Paris, because the gypsum which was used to get the powder was mainly found in Paris.

Notes:
Cassiterite is a mineral that is a significant ore of tin. It is also known as tin oxide. Although rare, its key characteristic is its high specific gravity that makes it easy to separate it from other materials. Tin, which is extracted from Cassiterite, is commonly used in making alloys, punches, and cutting tools.

Notes:
In 17 carat gold, the composition is 17 parts gold and 7 parts other metals, making it 70.6% gold. The term “carat” refers to the purity of gold, with 24 carats being pure gold. Thus, 17 carat gold contains 7 parts of other metals, which can include copper, silver, or palladium, used to enhance durability and alter color.

Notes:
Carbamide is another name of Urea, an organic compound with chemical formula CO(NH₂)₂. This name indicates that Urea is an amide in which two –NH₂ groups are joined by a carbonyl (C=O) functional group.

Notes:
Normal rainfall is slightly acidic due to the presence of carbonic acid, which forms when carbon dioxide (CO2) dissolves in water. The pH of normal rainwater is typically around 5.6, making it mildly acidic. This natural acidity is a result of the CO2 in the atmosphere, which is produced by respiration, combustion, and other natural processes.

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The atomic and ionic radii of the alkaline earth metals are smaller than corresponding alkali metals in the same periods due to the increased nuclear charge in these elements.

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Carbon dioxide can be obtained as a solid in the form of dry ice by allowing the liquified CO₂ to expand rapidly.

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The cells are called Direct-formic acid fuel cells, in which formic acid is directly fed in the cells. Storage of formic acid is much easier and safer than that of hydrogen because it does not need to be done at high pressures and (or) low temperatures, as formic acid is a liquid at standard temperature and pressure. Formic acid does not cross over the polymer membrane, so its efficiency can be higher than that of methanol. Use of acetic acid in cells does not arise.

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Crystallisation is a process that separates a pure solid in the form of its crystals from a solution. For example: purification of the salt obtained from sea water.

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Sphalerite (ZnS) is a sulphide. All others are oxides. Haematite and Magnetite are the oxides of iron and Cuprite is an oxide of Copper.