In this article, we delve into the essential organic compounds that candidates should be familiar with for their UPSC Prelims preparation. These compounds include hydrocarbons, alcohols, phenols, aldehydes, ketones, carboxylic acids, esters, ethers, amines, amides, and more. Understanding the nomenclature, reactions, and applications of these compounds is vital for tackling questions related to organic chemistry in the UPSC Prelims.
- Directions (Q. Nos. 45 and 46) The following items consist of two statements, ‘Assertion (A)’ and the other as ‘Reason (R)’. Examine these two statements carefully and select the answers to these items using the codes given below.
- Codes
- (a) Both A and R are true, and R is the correct explanation of A
- (b) Both A and R are true, but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Q45. Assertion (A) Formic acid is a stronger acid than acetic acid. (1998)
Reason (R) Formic acid is an organic acid.
Ans. (b)
Exp. Both A and R are true, but R is not the correct explanation of A. Formic acid (HCOOH) is a stronger acid than acetic acid (CH3COOH).
Methyl group (CH-) present in acetic acid molecule has electron donating nature i.e. it will increase the electron density over O-H bond. As a result, release of H+ ions from acetic acid will be more difficult. Further (CH3) group intensies the negative charge on the carboxylate ion there by making acetate ion less stable that formate ion. Formic acid is an organic acid because organic acid is an organic compound with acidic properties e.g. carboxylic acid. i CHC-O-H While inorganic acid or mineral acids are those acids which are derived from one or more inorganic compounds eg H₂SO₄ (sulphuric acid).
Q46. Assertion (A) Phenyl is used as a household germicide.
Reason (R) Phenyl is a phenol derivative and phenol are an effective germicide. (1998)
Ans. (a)
Exp. Both A and R are true, and R is the correct explanation of A Phenyl is used as a household germicide because it kills of prevent.
The growth of microorganism and the reason is true because phenyl being a phenol derivative possess effective germicidal in both strong properties because phenol acts as concentration solution (disinfectant) and its low concentration solution (antiseptic)
Q47. Consider the following statements about acetylene.
1. It is used in welding industry.
2. It is a raw material for preparing plastics.
3. It is easily obtained by mixing silicon carbide and
water.
Of these statement
(a) 1 and 2 are correct
(b) 1 and 3 are correct
(c) 2 and 3 are correct
(d) 1,2 and 3 are correct
Ans. (a)
Exp Statements (1) and (2) are correct. Acetylene or ethyne
(CHCH) is used in welding industry and also as a raw material for preparing plastics. Welding refers to the process of joining two or more metals.
together. Combustion of acetylene with oxygen produces a flame of over 3600 K. Oxyacetylene is the hottest burning common fuel gas. Following chemical reaction occur during the process.
2C₂H₂ +502 4CO2 + 2H2O2
The polymerization of acetylene with Ziegler-Natta catalyst produces polyacetylene films (show below).
Statement 3 is incorrect because acetylene cannot be obtained by mixing silicon carbide and water as the reaction gives methane.
- Note Polymerization is the process by which small repeating unit combine to form a large molecule or polymer.
Q48. Which one of the following statements regarding starch and cellulose is not correct? (1998)
(a) Both of them are of plant origin
(b) Both of them are polymers
(c) Both of them give color with iodine
(d) Both of them are made-up of glucose molecules
Ans. (c)
Exp. Statement (c) is not correct because iodine gives blue color with starch but not with cellulose.
Q49. Match List I (fuel gases) with List II (major constituents) and select the correct answer using the codes given below the lists. (2004)
List I List II
A. CNG Carbon monoxide, hydrogen
B. Coal gas Butane, propane
C. LPG Methane, ethane
D. Water gas Hydrogen, methane, carbon monoxide
Codes A B C D A B C D (a) 2 1 3 4 (c) 2 4 3 1 (b) 3 4 2 1 (d) 3 1 2 4
Ans. (b) 4
Exp. The correct matching is A-3, B-4, C-2, D-1.
- The main constituents of CNG are methane and ethane.
- The main constituents of coal gas are hydrogen, methane and CO.
- LPG has majorly butane and propane, water gas has majorly CO and hydrogen.
Q50. Consider the following statements.
(2005)
- Liquefied Natural Gas (LNG) is liquefied under extremely cold temperature and high pressure to facilitate storage or transportation in specially designed vessels.
- First LNG terminal in India was built in Hassan.
- Natural Gas Liquids (NGL) are separated from LPG, and these include ethane, propane, butane and natural gasoline.
Which of the statements given above is/are correct?
(a) Only 1
(b) 1 and 3
(c) 2 and 3
(d) 1, 2, and 3
Ans. (b)
Exp. Statements (1) and (3) are correct. LNG is natural gas cooled to an extremely low temperature (-160°C). Liquefied Natural Gas (LNG) is an alternative to oil and naphtha is about to land on Indian shores. LNG will be much cheaper than oil or naphtha. Natural Gas Liquids (NGL) are separated from LPG, and these include ethane, propane, butane and natural gasoline.
Statement (2) is incorrect because first LNG terminal in India was built in Daheja, Gujarat.
Q51. Assertion (A) The main constituent of the liquefied petroleum gas is methane. (2005)
Reason (R) Methane can be used directly for burning in homes and factories where it can be supplied through pipelines.
Codes
(a) Both A and Rare true and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Ans. (d)
Exp. A is false, but R is true. LPG like all fossil fuels, it is a non-renewable source of energy. It is extracted from crude oil and natural gas. The normal components of LPG are propane (C₂H₂) and butane (C4H10) Small concentrations of other hydrocarbons may also be present. It can be easily condensed, packaged, stored and utilized, which makes it an ideal energy source for a wide range of applications. Normally, the gas is stored in liquid form under pressure in steel container, cylinder or tank.
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