Chemistry MCQs

Notes:
Chemical formula of methyl isocyanate is C2H3NO. It is the gas leaked during the Bhopal gas tragedy incident. Methyl isocyanate is colourless and poisonous gas.

Notes:
The outermost orbital shell of an atom is called its valence shell, and the electrons in the valence shell are valence electrons. Valence electrons are the highest energy electrons in an atom and are therefore the most reactive. While inner electrons typically don’t participate in chemical bonding and reactions, valence electrons can be gained, lost, or shared to form chemical bonds.

Notes:
Ions are created when an atom loses or gains an electron. When an atom loses an electron, it becomes a cation (positive ion); when it gains an electron, it becomes an anion. So, when helium atom loses an electron, it becomes positively charged ion, i.e., it becomes a cation.

Notes:
The 1959 WHO International Standards for Drinking Water suggested that concentrations of copper greater than 1.5 mg/litre would markedly impair the potability of the water. However, in the first edition of the Guidelines for Drinking Water Quality, published in 1984, a guideline value of 1.0 mg/litre was established for copper, based on its laundry and other staining properties.

Notes:
Some elements behave chemically both as metals and nonmetals, and are called metalloids. There are total eight of them such as Boron, Silicon, Germanium and Antimony. Most of these elements are used in doping of semiconductors. Elements which are neither metals nor non-metals are called Noble or Inert Gases.

Notes:
Silver is a fairly stable metal and under normal circumstances does not corrode quickly. However, it is particularly susceptible to the effects of the sulfide radical. When exposed to air, silver reacts with Hydrogen sulphide in the atmosphere, especially in marine environment, and readily forms a blackish surface tarnish of silver sulphide.

• 2Ag + H2S —> Ag2S +H2

Notes:
An inert gas is a gas which does not undergo chemical reactions since its valence shells is filled, meaning it does normally form chemical bonds with other elements. These gases are extremely stable; they rarely gain, lose or share electrons.The six inert gases, also called noble gases, are argon, helium, neon, krypton, xenon and radon.

Notes:
Brine is a high-concentration solution of salt (usually sodium chloride) in water. It is mainly used as a preservative for vegetables, fish, fruit, and meat through a process known as brining. The high salt content in Brine prevents the growth of bacteria and thus helps to preserve the food for a long time without creating any difference in taste.

Notes:
Pure nitric acid is a colorless fuming liquid with a pungent odor. Nitric acid obtained in laboratory is slightly yellow due to the dissolution of nitrogen dioxide which is produced due to thermal decomposition of a portion of HNO3.

• 4HNO3 <— 2H2O + 4NO2 + O2

Notes:
Dry ice, sometimes referred to as “cardice,” is the solid form of carbon dioxide. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is used primarily as a cooling agent in preserving frozen foods.