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All questions of Acids, Bases & Salts for UPSC CSE Exam

When lime juice is dropped on baking soda, brisk effervescence takes place because the gas evolved is
  • a)
    Hydrogen
  • b)
    1. Oxygen
  • c)
    Carbon dioxide
  • d)
    None of the above
Correct answer is option 'C'. Can you explain this answer?

Paradigm Institute answered
  • Lime juice is basically citric acid found in lemon and baking soda is Sodium Bicarbonate. 
  • When these two react, salt and water along with carbon dioxide are formed. 
  • This carbon dioxide is the reason for brisk effervescence observed when the reaction takes place. 
  • Carbon dioxide is a heat-trapping gas released in large quantities from the burning of fossil fuels, industries, and other human activities. 
  • C6H8O7 (Citric Acid) + 3NaHCO3 (Baking Soda) ⇒ 3CO2(gas) + 3H2O (water) + Na3C6H5O7 (Salt- Sodium citrate)
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Which of the following acid is found in Nettle plant?
  • a)
    Methanoic acid
  • b)
    Citric Acid
  • c)
    Ethanoic Acid
  • d)
    Oxalic acid
Correct answer is option 'A'. Can you explain this answer?

Paradigm Institute answered
  • Nettle is an herbaceous plant that grows in the wild.
  • Nettle leaves have stinging hair, which causes painful stings when touched accidentally. 
  • This is due to the methanoic acid secreted by them. 
  • A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle.

What is the pH value of acid rain?
  • a)
    Less than 5.6
  • b)
    More than 5.6
  • c)
    Equal to 7.0 
  • d)
    5.62. More than 5.63. Equal to 7.0 
Correct answer is option 'A'. Can you explain this answer?

Catalyst Learningacademy answered
  • Acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are discharged into the air.
  • These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.
  • Human activities are the main cause of acid rain.
  • Over the past few decades, humans have released so many different chemicals into the air that they have changed the mix of gases in the atmosphere.
  • Power plants release the majority of sulfur dioxide and much of the nitrogen oxides when they burn fossil fuels, such as coal, to produce electricity.
  • Besides, the exhausts from cars, trucks, and buses release nitrogen oxides and sulfur dioxide into the air. These pollutants cause acid rain.

Which type of medicines are used for treating indigestion?
  • a)
    Antibiotic
  • b)
    Analgesic
  • c)
    Antacid
  • d)
    Antiseptic
Correct answer is option 'C'. Can you explain this answer?

Paradigm Institute answered
Antacid:
  • Antacids are medicines that counteract (neutralize) the acid in your stomach to relieve indigestion and heartburn.
  • Antacids may help if you have: 
    • Indigestion
    • Heartburn or acid reflux – also known as gastro-oesophageal reflux disease (GORD)
    • Stomach ulcer
    • Gastritis (inflammation of the stomach lining) 

Which colour appears when few drops of phenolphthalein are put into a test tube containing lime water?
  • a)
    Yellow
  • b)
    Pink
  • c)
    Orange
  • d)
    Colourless
Correct answer is option 'B'. Can you explain this answer?

Catalyst Learningacademy answered
  • The chemical compound phenolphthalein has the formula C20H14O4 and is commonly abbreviated as "HIn" or "phph" in shorthand notation.
  • Phenolphthalein is frequently used as an indicator.
  • It's a phthalein dye, which means it's a type of dye.
  • Phenolphthalein in Acidic solutions turns colourless
  • Phenolphthalein in basic solutions turns pink in colour. 
Explanation:
  • Lime water is basic in nature. 
  • Calcium hydroxide is the chemical term for lime water, which has the formula Ca(OH)2.
  • When Phenolphthalein, it turns pink as lime water is basic in nature.
  • Hence, the correct answer is - Pink.

3 Solutions A, B and C are taken in a test tube. On adding China rose indicator, A turned green, B remained colourlers whereas C turned dark pink in colour.
What is the nature of A, B and C ?
  • a)
    A - Acidic, B- Basic, C - Salt
  • b)
    A - Basic, B - Acidic, C - Salt
  • c)
    A - Salt, B - Basic, C - Acidic
  • d)
    A - Basic, B - Salt, C -Acidic
Correct answer is option 'D'. Can you explain this answer?

Catalyst Learningacademy answered
A turning green with China rose indicator suggests that it is a basic solution. China rose indicator is a pH indicator that changes color in the presence of acidic and basic solutions. In this case, the green color indicates that solution A has a basic nature.
B remaining colorless with China rose indicator suggests that it is a neutral solution. The lack of color change indicates that solution B has a pH value close to 7, which is considered neutral on the pH scale.
C turning dark pink in color with China rose indicator suggests that it is an acidic solution. China rose indicator turns pink or dark pink in the presence of acidic solutions, indicating that solution C has an acidic nature.

Lemon fruit is a rich source of 
  • a)
    malic acid
  • b)
    citric acid
  • c)
    tartaric acid
  • d)
    acetic acid
Correct answer is option 'B'. Can you explain this answer?

Paradigm Institute answered
Lemon fruit is a rich source of citric acid.
  • Citric acid is a weak organic acid.
  • It is a six-carbon tricarboxylic acid.
  • A manufactured form of citric acid is commonly used as an additive in food, cleaning agents, and nutritional supplements.
  • Citric acid is mainly produced by fungal fermentation.
  • Chemical synthesis of citric acid is possible, but it is expensive than fungal fermentation.

Which of the following acid is found in human stomach?
  • a)
    Hydrochloric acid
  • b)
    Sulfuric acid
  • c)
    Nitric acid
  • d)
    Acetic acid
Correct answer is option 'A'. Can you explain this answer?

Paradigm Institute answered
  • Hydrochloric acid is found in the human stomach.
  • Formula- HCl
  • Hydrochloric acid helps in digestion by breaking complex large food molecules into simpler molecules.
  • The acid activates the pepsinogen enzyme required to digest proteins.
  • It also kills harmful microorganisms present in the stomach.
  • It is also known as muriatic acid

Which acid does an ant sting possess?
  • a)
    Methanoic acid
  • b)
    Oxalic acid
  • c)
    Lactic acid
  • d)
    Citric acid
Correct answer is option 'A'. Can you explain this answer?

Catalyst Learningacademy answered
The correct answer is Methanoic acid.
  • The acid present in an ant sting is Formic acid.
  • Formic acid (systematically called methanoic acid) is the simplest carboxylic acid.
  • Molecular formula: HCOOH
  • It is quite fatal for those ants as after stinging, their stinger is lost and they forcibly release formic acid from their poison gland.
Important Points
  • Oxalic acid is an organic compound found in many plants. These include leafy greens, vegetables, fruits, cocoa, nuts, and seeds
  • Lactic acid is a natural organic acid, found in milk and other food products such as meat and beer.
    • It is used in the food industry as a preservative, flavor enhancer, and acid adjustment.
  • Citric acid is found naturally in citrus fruits, like lemons and limes.
    • It gives them their tart, sour taste.

Which of the following substances can be used for identifying an acid solution?
  • a)
    NaCl
  • b)
    KNO3
  • c)
    Na2CO3
  • d)
    K2SO4
Correct answer is option 'B'. Can you explain this answer?

Catalyst Learningacademy answered
Acid: The compound that produces hydrogen ion when it dissolved in the solution is called acid.
  • The acidic property depends on the concentration of the Hydrogen ion in the solution.
  • H+ ion cannot exist alone. It always conjugates with the water and forms hydronium ion(H3O+)
The identification of the acidic or basic nature of any salt solution by the reactions:
  • Strong acid + strong base → water + neutral salt
  • Weak acid + strong base → water + basic salt
  • Strong acid + weak base → water + acidic salt
  • Weak acid + weak base → water + salt (It may be a neutral, acidic, or basic depending on the reactants used in the reaction)
EXPLANATION:
  • KNO3 is completely ionized in the water that gives the Nitric acid which is a strong acid. So KNO3 can be used for identifying an acid solution. Hence option 2 is correct.
  • The K+ is an unreactive ion because it is produced from the dissolution of the strong base (KOH). So K2SO4 can't be used to identify the acidic solution.
  • NaCl is a neutral solution that's why we can't use it also.
  • Since Na2CO3 is formed by a weak acid Carbonic acid (H2CO3). That's why it can't be used also.

Chapter doubts & questions for Acids, Bases & Salts - Lucent for GK 2025 is part of UPSC CSE exam preparation. The chapters have been prepared according to the UPSC CSE exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for UPSC CSE 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.

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