Chemistry - Study Mode

[#646] Helium gas is filled in balloons because
Correct Answer

(B) It is lighter than air

Explanation

Solution: Because of the Archimedes’ principle, a lifting gas is required for aerostats to create buoyancy. Its density is lower than that of air (about 1.29 kg/m 3 , 1.29 g/ L). Only certain lighter than air gases are suitable as lifting gases. Hydrogen and helium are the most commonly used lift gases. Although helium is twice as heavy as (diatomic) hydrogen, they are both so much lighter than air that this difference is inconsequential. Both provide about 9.8 N of lift (1 Newton is the force required to accelerate 1 kg at 1 m/sec 2 ) per cubic meter of gas at STP. Helium is the second lightest gas. For that reason, it is an attractive gas for lifting as well. A major advantage is that this gas is noncombustible. Today helium is used instead of hydrogen, since it is inert so non-flammable which makes things a lot safer. Hydrogen can ignite very easily when mixed with the oxygen of the surrounding air.

[#647] The inert gas which is substituted for nitrogen in the air used by deep sea divers for breathing is
Correct Answer

(D) Helium

Explanation

Solution: Trimix is a mixture of oxygen, nitrogen and helium and is often used at depth in technical diving and commercial diving instead of air to reduce nitrogen narcosis and to avoid the dangers of oxygen toxicity.

[#648] At room temperature, the metal that remains liquid is:
Correct Answer

(A) Mercury

Explanation

Solution: At room temperature, the metal that remains liquid is mercury.

[#649] A metal is exposed to the atmosphere for sometime. It becomes coated with green carbonate. The metal must be
Correct Answer

(B) Copper

Explanation

Solution: Copper forms a rich variety of compounds with oxidation states +1 and +2, which are often called cuprous and cupric, respectively. It does not react with water, but it slowly reacts with atmospheric oxygen forming a layer of brown-black copper oxide. In contrast to the oxidation of iron by wet air, this oxide layer stops the further, bulk corrosion. A green layer of verdigris (copper carbonate) can often be seen on old copper constructions, such as the Statue of Liberty, the largest copper statue in the world built using repoussé and chasing. Hydrogen sulphides and sulphides react with copper to form various copper sulphides on the surface. In the latter case, the copper corrodes, as is seen when copper is exposed to air containing sulfur compounds. Oxygen-containing ammonia solutions give water-soluble complexes with copper, as do oxygen and hydrochloric acid to form copper chlorides and acidified hydrogen peroxide to form copper(II) salts. Copper(II) chloride and copper combine to form copper(I) chloride.

[#650] Which of the following is very reactive and kept in kerosene?
Correct Answer

(A) Sodium

Explanation

Solution: Sodium is a very reactive metal. It reacts vigorously with oxygen and water. A lot of heat is generated in this process. Therefore, it is stored in kerosene to avoid contacts between either atmospheric oxygen or water.