CHEMISTRY [2 Mark Question Answer]

When carbon dioxide is passed through lime water in a small amount, it turns milky due to the formation of insoluble calcium carbonate.

If excess of carbon dioxide is passed through the milky suspension, the solution becomes clear due to the formation of soluble calcium bicarbonate.

The burning splinter gets extinguished as carbon dioxide does not support combustion.

Carbon dioxide turns blue litmus red.

Because of its inert nature, nitrogen is used in food packaging. The containers used for storing foodstuffs are flushed with nitrogen to remove oxygen before they are sealed. The absence of oxygen does not allow bacterial growth. Thus, food stufs remain fresh for a long time.

As carbon dioxide is neither combustible nor a supporter of combustion, it is used in fire extinguishers to put out fire. Being heavier than air, it settles and forms a blanket over the fire and thus cuts off the supply of oxygen to put off the fire.

Solid carbon dioxide (dry ice) is used for the refrigeration of food as it gives – 40°C temperature, sublimes and is non- poisonous.

Oxygen is collected by the downward displacement of water as oxygen is very slightly soluble in water and it cannot be collected over air since it is almost as heavy as air. So it displaces water downwards and the oxygen gas gets collected above water in jar.

The process of converting free nitrogen of the atmosphere into nitrogen compounds such as ammonia and nitrates is called nitrogen fixation. In nature, it is done by nitrogen-fixing bacteria in soil or root nodules of legumes. Lightning also converts nitrogen gas to nitrate compounds.

The phenomenon of increasing air temperature near the earth’s surface is called global warming. The increasing carbon dioxide level in the atmosphere has led to excessive heating of the earth’s surface.

Green house effect is a natural effect occurring in the atmosphere because of centrain gases that absorb heat energy radiated from the earth’s surface and reradiate it back to the earth’s surface. The major green house gases are carbon- dioxide, methane and water vapour.

Dry ice is solid carbon dioxide which gives -40°C, sublimes and is non-poisonous. It is used as a refrigerant for preserving food items such as vegetables, fruits and meat.

Galvanization is a process that involves coating iron with a thin layer of zinc to prevent rusting of iron. As zinc is more reactive than iron, it reacts with oxygen in the presence of moisture and prevents iron from msting. Iron coated with zinc is called galvanized iron (GI).

When an iron object is exposed to moist air, its surface gets covered with a reddish brown powder called rust. Two conditions necessary for rusting to take place :
(i) Presence of air (or oxygen)
(b) Presence of water (or moisture).

When red lead oxide is heated, lead monoxide is formed along with oxygen gas. Oxygen gas can be prepared by this method.