Chemistry MCQs

Notes:
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, a notable exception being iron. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore. Dentistry has used alloys of mercury with metals such as silver, copper, indium, tin and zinc. Amalgam is an “excellent and versatile restorative material” and is used in dentistry for a number of reasons.

Notes:
Fermentation is an anaerobic chemical process that breaks down glucose molecules. In baking, yeast consumes sugar and converts it into carbon dioxide and alcohol, making the dough rise. This gas gets trapped in the strands of gluten, resulting in air pockets that cause the dough to rise and form the characteristic spongy texture of bread and cakes. Further, the creation of lactic and acetic acids during fermentation augments this dough handling process, improves flavor, enhances the texture, and extends the shelf-life of the baked products.

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When cathode rays strike a solid target of high atomic weight and high melting point such as tungsten, molybdenum, etc, they give rise to a highly penetrating radiation called the X-rays.

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In 1905, it was Einstein who suggested the concept of light having a dual nature; particle and wave nature. In a similar way, Louise de Broglie suggested that electron also exhibits a dual nature. Broglie derived a mathematical expression to prove the wave nature of electron along with particle nature. He gave the following relation:- O = h/mv, where O is the wavelength of electron, m is mass of an electron and v is the frequency.

Notes:
Anions are negative ions that are formed when a non-metal atom gains one or more electrons. They are formed by the addition of electrons. Anions are so named because they are attracted to the anode (positive field) in an electric field. Atoms typically gain electrons so that they will have the electron configuration of a noble gas.

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Aluminum powder is a highly flammable powder produced by grinding aluminum into fine grains of material. Aluminium powder is used to reduce iron oxide in aluminothermy process to produce iron (molten) for welding. Piece of magnesium are used to charge toe mixture.

• Fe2O3 + 2Al —> Al2O3 + 2Fe

Notes:
All acids contain hydrogen atom (s). In aqueons state, they produce hydrogen ions. Dilute acids react with some metals that are more electro positive than hydrogen such as Sodium, Potassium, Calcium, iron, etc to form salts. Sodium replaces two hydrogen atoms from Sulfuric acid (H2SO4) to form a normal salt, Sodium Sulphate (Na2SO4). If only one atom of hydrogen is replaced by sodium, it forms an acid salt, Sodium Hydrogen Sulphate (NaHSO4).

Notes:
Bakelite is a poor conductor of heat and electricity. It is a thermosetting plastic that has very high internal resistance that resist the circuit current flow through it. One of the first plastics made from synthetic components, it was used for its electrical non–conductivity and heat-resistant properties in electrical insulators and products such as kitchenware, jewelry, children’s toys, firearms, etc.

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Rock salt is the mineral (natural) form of sodium chloride (NaCl). It has high quantities of phosphorous, calcium, potassium, iron, magnesium, zinc, selenium, copper, bromine, zirconium and iodine. All of these minerals occur naturally.

Notes:
Metals are good conductors of heat. This is because:

• a) Metal ions are closely packed in the metal lattice and thus the transfer of heat from one end to another is more efficient.
• b) Availability of free electrons makes transfer of heat easier making it a good conductor of heat.