Chemistry MCQs

Notes:
Distilled water is considered the purest form of water. The process of distillation involves boiling the water and then condensing the vapor back into a liquid. It removes all impurities, ions, minerals, and contaminants present in the water. Tap, ground, and rainwater, although natural sources of water, are subject to various forms of adulteration and pollution.

Notes:
The synthase enzyme converts the amino acids sulfoxides of the onion into sulfenic acid.

• The unstable sulfenic acid rearranges itself into synropanethial-S-oxide.
• Citric acid is a weak organic acid that occurs naturally in citrus fruits.
• Nitric acid is a highly corrosive mineral acid.
• Sulphuric acid is a mineral acid composed of the elements sulfur, oxygen and hydrogen.

Notes:
Copper is deposited at the cathode and is dissolved at the anode. Consequently the concentration of copper ions in solution remains constant. This can be used as a method of purification of copper as only pure copper is deposited at the cathode. Bubbles of gas (oxygen) are formed and evolved at the anode.

• Cathode reaction: Cu2+ + (aq) + 2e– —> Cu(s); and
• Anode reaction: 2H2O(l ) —> O2(g) + 4H+(aq) + 4e-

Notes:
During respiration, glucose molecules are converted to other molecules in a series of steps. They finally end up as carbon dioxide and water. The reaction is exothermic because the C=O and O-H bonds in the products are so much more stable than the bonds in the reactants.

Notes:
A catalyst is an agent or compound that increases the rate of a reaction without itself being consumed. Enzymes are naturally occurring catalysts responsible for many essential biochemical reactions. Most solid catalysts are metals or the oxides, sulfides, and halides of metallic elements and of the semi-metallic elements boron, aluminum, and silicon.

Notes:
A thermonuclear weapon is a nuclear weapon design that uses the heat generated by a fission bomb to compress a nuclear fusion stage which indirectly results in greatly increased energy yield (i.e., bomb “power”). It is colloquially referred to as a hydrogen bomb or H-bomb because it employs hydrogen fusion, though in most applications the majority of its destructive energy comes from uranium fission, not hydrogen fusion by itself.

Notes:
An antiknock agent is a gasoline additive used to reduce engine knocking and increase the fuel’s octane rating by raising the temperature and pressure at which ignition occurs. Tetraethyl lead was admixed with gasoline (petrol) beginning in the 1920s as an inexpensive octane booster which allowed engine compression to be raised substantially, which in turn increased vehicle performance and fuel economy.

Notes:
Bunker Gear or “Turnout Gear” are terms used by many firefighters to refer to their system of outer protective clothing. Fire fighter used to be made of asbestos in the past. However, because of its carcinogenic properties and other harmful effects, it has slowly been replaced by other substitutes. Fire-fighting and working clothes and accessories for firemen, rescuers and industrials made of materials FR cotton, Nomex, Modacryl, FR viscose and others.

Notes:
Amines are organic derivatives of ammonia, in which one, two, or all three of the hydrogens of ammonia are replaced by organic groups. All aliphatic primary amines are stronger bases than ammonia. In aqueous solution, the pKb’s (basicity) of ammonia, methyl amine, dimethylamine, and trimethyl amine are therefore, respectively, 4.74, 3.34, 3.27. and 4.19. In terms of pKb, the strongest bases have the least positive values of pKb. So in aqueous solutions, the strongest bases are:

• Dimethylamine > Methylamine > trimethylamine > Ammonia.

Notes:
Liquefied petroleum gas (LPG) is mostly propane (C3H8), mostly butane (C4H10) and, most commonly, mixes including both propane and butane. In the northern hemisphere winter, the mixes contain more propane, while in summer, they contain more butane.