Chemistry - Study Mode

[#251] Which one of the following is used for dating very old objects of archaeological importance?
Correct Answer

(D) Carbon-14

Explanation

Solution: Radiocarbon dating (usually referred to as simply carbon dating) is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 (14C) to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. After plants die or they are consumed by other organisms (for example, by humans or other animals), the incorporation of all carbon isotopes, including 14C, stops. Thereafter, the concentration (fraction) of 14C declines at a fixed exponential rate due to the radioactive decay of 14C.

[#252] In which of the following substances all carbon atoms are quaternary in nature ?
Correct Answer

(B) Diamond

Explanation

Solution: Carbon atoms in diamond are quaternary in nature. The crystal structure of a diamond is a face-centered cubic or FCC lattice. Each carbon atom joins four other carbon atoms in regular tetrahedrons (triangular prisms). Based on the cubic form and its highly symmetrical arrangement of atoms, diamond crystals can develop into several different shapes, known as ‘crystal habits’.

[#253] When lime juice is dropped on baking soda, brisk effervescence takes place because the gas evolved is
Correct Answer

(C) Carbon dioxide

Explanation

Solution: When baking soda and lemon juice are added together, the reaction of the two is an acid-based reaction because it involves an acid (citric acid in the lemon juice) reacting with a base (sodium bicarbonate, more commonly known as baking soda). Carbon dioxide, a gas, is produced by the reaction.

[#254] Which of the following is used as filler in tyre of rubber ?
Correct Answer

(A) Carbon black

Explanation

Solution: The most common use (70%) of carbon black is as a pigment and reinforcing phase in automobile tires. Carbon black also helps conduct heat away from the tread and belt area of the tire, reducing thermal damage and increasing tire life. Carbon black particles are also employed in some radar absorbent materials and in photocopier and laser printer toner. It is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil.

[#255] The open "Sigrees" or coal stoves often require fanning to sustain burning because of
Correct Answer

(A) Tendency of carbon dioxide to form a layer along with dust smoke

Explanation

Solution: Burning coal requires oxygen to chemically react. The availability of oxygen is limited in the furnace by several factors such as the friction of the air against the coal. Blowing provides more oxygen to the flame and raises the temperature of the flame. Besides, it helps to prevent carbon dioxide from forming layer along with dust smoke so as to keep the supply of oxygen intact.