OAS Prelims-2020 Daily Practice Set-05/01/2021: Chemistry

1. Baryllium Sulphate is less soluble in water due to:
a) High inflammable energy
b) Low Energy of dissociation
c) Low inflammable energy
c) Lonic band

2. What is the name of that system, which uses radioactivity to decide the period of materials of-pre-historic period ?
a) Radium dating
b) Uranium dating
c) Carbon dating
d) Deuterium dating

3. Cement is made hard with:
a) dehydration
b) hydration and dissociation of water
c) Dissociation of water
d) Polymerisation

4. What happens when a chemical bond is formed ?
a) energy is always absorbed
b) energy in always released
c) more energy is released than is absorbed
d) energy is neither released nor absorbed

5. Which among the following is a carbohydrate ?
a) Nylon
b) Cane-sugar
c) Turpentine
d) Hydrogen peroxide

6. In which of the following states maximum iron ore is found ?
a) FeCO3
b) Fe2O3
c) Fe3O4
d) FeS2

7. “All the four quantum numbers of two electrons in an atom are not the same.” It is the law of —
a) Hund’s
b) Exclusion Principle of Pauli
c) Uncertainty Principle of Hiesenberg
d) Avogadro’s Law

8. Commercial nitric acid is coloured because it contains dissolved :
a) Oxygen
b) Nitrous oxide
c) Nitrogen dioxide
d) Coloured impurities

9. Fertiliser having high nitrogen content is :
a) Urea
b) Ammonium sulphate
c) Ammonium nitrate
d) Calcium citrate

10. Where does the oxygen that keeps us alive come from?
a) Carbon dioxide
b) Carbonates absorbed from soil
c) Oxides of minerals
d) Water


Answers and Explanations

1. (a) Baryllium sulfate (BeSO4) is a white crystalline solid. It was first isolated in 1815 by Jons Jakob Berzelius. Beryllium sulfate may be prepared by treating an aqueous solution of any beryllium salt with sulfuric acid, followed by evaporation of the solution and crystallization. The hydrated product may be converted to anhydrous salt by heating at 400°C. Baryllium Sulphate is less soluble in water due to High inflammable energy.

2. (c) 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.

3. (b) Cements (e.g., Portland cement) harden because of hydration, chemical reactions that occur independently of the mixture’s water content; they can harden even underwater or when constantly exposed to wet weather. The chemical reaction that results when the anhydrous cement powder is mixed with water produces hydrates that are not watersoluble.

4. (a) If a bond is broken, energy is released; and if a bond is formed, energy must have been absorbed. As these occur, a change in the chemical energy of the system also occurs. Within each bond of a molecule is an experimentally determined amount of energy that upon the breaking of that bond is released into the chemical system. The energy within these bonds are ‘stored’ and can be easily thought of as potential energy. Upon the breaking of these bonds the energy is released thereby creating usable energy.

5. (b) Cane-sugar is carbohydrate and as this name implies, is composed of carbon, hydrogen and oxygen. it is a source of extracting sugar. There are various types of sugar derived from different sources. Simple sugars are called monosaccharides and include glucose, fructose and galactose. The table or granulated sugar most customarily used as food is sucrose, a disaccharide. Other disaccharides include maltose and lactose.

6. (b) Iron ores are rocks and minerals from which metallic iron can be economically extracted. The iron itself is usually found in the form of magnetite (Fe3O4), hematite (Fe2O3), goethite (FeO(OH), limonite (FeO(OH).n(H2O)) or siderite (FeCO3). Hematite, also spelled as haematite, is the mineral form of iron(III) oxide (Fe2O3), one of several iron oxides. It is mined as the main ore of iron. Huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places where there has been standing water or mineral hot springs, such as those in Yellowstone National Park in the United States.

7. (b) The Pauli exclusion principle is the quantum mechanical principle that no two identical fermions (particles with half-integer spin) may occupy the same quantum state simultaneously. A more rigorous statement is that the total wave function for two identical fermions is anti-symmetric with respect to exchange of the particles. For example, no two electrons in a single atom can have the same four quantum numbers; if n, l, and ml are the same, ms must be different such that the electrons have opposite spins.

8. (c) Commercial nitric acid has a brown colour due to dissolved NO 2. The procedure of bubbling dry air through warm commercial nitric acid, is to drive away the dissolved nitrogen dioxide so that the acid becomes colourless.

9. (c) A growth fertilizer will have a high N content and relatively low P and K content. Ammonium nitrate is the highest Nitrogen fertilizer you can buy, and it is potent stuff. It is usually rated as 33-0-0 or 34-0-0. The bag contains 33% or 34% Nitrogen and the other 66% or 67% is inert material. Other formulations of growth fertilizers will contain 5, 6 or even 7 times more Nitrogen than anything else.

10. (d) Since water and carbon dioxide are both compounds which contain oxygen, it is possible to obtain oxygen from either. The oxygen produced from photosynthesis is not released into the air. It is not until cellular respiration that oxygen is released. The oxygen comes from water. The water molecules are split at the “beginning” of photosynthesis for the electrons. These electrons eventually make their way to the electron transport chain, where oxygen is the final electron accept, and then released into the air. Scientists agree that there’s oxygen from ocean plants in every breath we take. Most of this oxygen comes from tiny ocean plants – called phytoplankton – that live near the water’s surface and drift with the currents. Like all plants, they photosynthesize – that is, they use sunlight and carbon dioxide to make food. A byproduct of photosynthesis is oxygen.

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