Chemistry - Study Mode

[#476] Copper substances when exposed to air gains a green coating due to the formation of:
Correct Answer

(B) CuCO 3 Cu(OH) 2

Explanation

Solution: When copper is exposed to air, it reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat. This green substance is basic copper carbonate (CuCO 3 . Cu (OH) 2 ). The formation of this green coating on the surface of a copper object corrodes it.

[#477] Browning of paper in old books is caused by
Correct Answer

(D) Oxidation of cellulose

Explanation

Solution: Foxing is a term describing the age-related spots and browning seen on vintage paper documents such as books, postage stamps, certificates, and so forth. It results from localized accelerated oxidation of cellulose or the effect on certain papers of the oxidation of iron, copper, etc.

[#478] When quick lime is added to water
Correct Answer

(A) Heat is liberated

Explanation

Solution: The quick lime reaction with water is exothermic in nature due to production of heat. The slaked lime creates a suspension in water since it is only slightly soluble in water. The clear solution formed after the slaked lime gets settled is also known as lime water.

[#479] What is the element that is in the highest percentage in the composition of the earth ?
Correct Answer

(B) Oxygen

Explanation

Solution: Oxygen has the highest percentage in both human body and on earth, but carbon, the element with the second highest percentage in the body, is relatively rare on Earth.

[#480] In sugar solution,
Correct Answer

(A) Sugar is solute, water is solvent

Explanation

Solution: When you stir a spoonful of sugar into a glass of water, you are forming a solution. This type of liquid solution is composed of a solid solute, which is the sugar, and a liquid solvent, which is the water. As the sugar molecules spread evenly throughout the water, the sugar dissolves.