Chemistry MCQs

Notes:
Nichrome has high melting point because it is very ductile. The metal is very hard and non-fragile. Nichrome is a non-magnetic alloy of nickel, chromium, and iron, usually used as a resistance wire. A common alloy is 80% nickel and 20% chromium, by mass. This alloying provide nichrome properties like hardness and ductility.

Notes:
In 1848, Lord Kelvin established concept of absolute zero, the temperature at which all molecular motion ceases.

Notes:
Both are correct statements.

Notes:
The chemical name of hypo is sodium thiosulfate. Chemical formula for hypo is Na2S2O3. Hypo is also called as hyposulphite of soda. Applications of hypo include photography, medicine, dechlorination of tap water, gold mining etc.

Notes:
Natural and wastewater contain small particulates that are suspended in water forming a colloid. These particles carry the same charges, and repulsion prevents them from combining into larger particulates to settle. Historically, dirty water is cleaned by treating with alum, Al2(SO4)3.12 H2O, and lime, Ca(OH)2. The phenomenon is known as coagulation:

• Al2(SO4)3.12 H2O Al(aq)3+ + 3SO4(aq)2- + 12H2O
• SO4(aq)2- + H2O HSO4(aq)- + OH- (causing pH change)
• Ca(OH)2 Ca(aq)2+ + 2 OH- (causing pH change)

The slightly basic water causes Al(OH)3, Fe(OH)3 and Fe(OH)2 to precipitate, bringing the small particulates with them and the water becomes clear.

Notes:
The atomic number is denoted by symbol Z. The symbol Z comes from the German word Zahl meaning number, which, prior to the modern synthesis of ideas from chemistry and physics, merely denoted an element’s numerical place in the periodic table. The sum of the atomic number Z and the number of neutrons, N, gives the mass number A of an atom.

Notes:
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:
Nitrogen is a major constituent of all proteins, and thus of all living organisms. The deficiency of nitrogen causes yellowing of older leaves, stunted plants, dormancy of lateral buds, purple colouration in shoot axis surface, wrinkling of cereal grains and inhibition of cell division. In humans, its deficiency cause PCM that leads to retarded body growth in form of Marasmus and kawashikor.

Notes:
There are a number of atmospheric gases which make up air. In the lower atmosphere or troposphere, the main gases are nitrogen and oxygen, which make up 78% and 21% of the volume of air respectively. The remaining 1% of the atmospheric gases is made up of trace gases.

Notes:
Cryolite (Na3AlF6, sodium hexafluoroaluminate) does not contain oxygen. It occurs as glassy, colorless, white-reddish to gray-black prismatic monoclinic crystals. Cryolite is used as an insecticide and a pesticide. It is also used to give fireworks a yellow color.