Miscellaneous — Chemistry

Q.1

WBCS Prelims 2013

One of the breakthroughs of Acharya P. C. Roy was to synthesize the following compound :

A. HgCl2

B. NH4NO2

C. Hg2Cl2

D. H2O4

Explanation

Why Correct: Acharya Prafulla Chandra Roy first synthesized ammonium nitrite (NH4NO2) in 1896, a landmark achievement in Indian chemistry.
Distractor Analysis: HgCl2 is mercuric chloride (corrosive sublimate). Hg2Cl2 is calomel (mercurous chloride). H2O4 is not a standard chemical formula; it might be a misrepresentation of hydrogen peroxide (H2O2) or other peroxides.
Takeaway: Acharya P.C. Roy also founded Bengal Chemicals & Pharmaceuticals, India's first pharmaceutical company.

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Q.2

WBCS Prelims 2008

Succinic acid dehydrogenase to give

A. Malic acid

B. Formic acid

C. Iso-citric acid

D. Fumaric acid

Explanation

Why Correct: Succinic acid undergoes dehydrogenation via succinate dehydrogenase in the Krebs cycle, losing two hydrogen atoms to form fumaric acid.
Distractor Analysis: Malic acid forms from fumaric acid via fumarase hydration. Formic acid is a simpler carboxylic acid not directly produced in this step. Iso-citric acid precedes succinic acid in the Krebs cycle, forming from citrate.
Takeaway: The Krebs cycle sequence is: citrate -> iso-citrate -> alpha-ketoglutarate -> succinyl-CoA -> succinate -> fumarate -> malate -> oxaloacetate.

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Q.3

WBCS Prelims 2005

Which one of the following is in the mixture of sympathetic ink?

A. Cobalt chloride and water

B. Zinc chloride and water

C. Magnesium chloride and water

D. None of the above

Explanation

Why Correct: Cobalt chloride dissolved in water forms a sympathetic ink that appears nearly invisible when dry and turns blue when hydrated.
Distractor Analysis: Zinc chloride solutions serve as wood preservatives and deodorants. Magnesium chloride solutions are used for dust control and food processing.
Takeaway: Sympathetic inks also include lemon juice (revealed by heat), phenolphthalein (revealed by alkaline solution), and copper sulfate (revealed by ammonia).

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Q.4

WBCS Prelims 2001

The most abundant ions in the Bay of Bengal water are

A. Na+ and Cl-

B. H+ and OH-

C. Mg2+ and SO42-

D. Fe2+ and Cl-

Explanation

Why Correct: Seawater contains sodium (Na+) and chloride (Cl-) ions at approximately 10,800 mg/L and 19,400 mg/L respectively, making them the most abundant ions by far.
Distractor Analysis: H+ and OH- ions exist in very low concentrations in neutral seawater (pH ~8.1). Mg2+ and SO42- are the second and third most abundant cations and anions respectively, but at much lower concentrations than Na+ and Cl-. Fe2+ is present only in trace amounts in seawater.
Takeaway: The major ions in seawater follow a consistent order: Cl- > Na+ > SO42- > Mg2+ > Ca2+ > K+, accounting for over 99% of dissolved solids.

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