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General Properties Questions

Chapter: Acids, Bases, and Salts | Total Available: 20 Real Questions

Question 1 of 10 Authentic UPSC NDA Question

Which one of the following solutions is not capable of conducting electricity?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (C) is correct. Sugar solution does not conduct electricity.

📖 Governing Law / Core Concept

A substance can only conduct electricity if it contains charged particles (ions) that are free to move. This is governed by the concept of electrolytic conduction.

🧪 Step-by-Step Breakdown

Sugar (C12H22O11) is a covalent compound. In aqueous solution, it dissolves but does not dissociate into ions:

C12H22O11 (s) → C12H22O11 (aq)

Since no ions are produced, sugar solutions do not conduct electricity, unlike ionic compounds like copper sulfate (CuSO4) or sodium chloride (NaCl), which dissociate and allow electrical current to pass.

🔍 Option Analysis

  • A: Copper sulphate (CuSO4) - Ionic compound, conducts electricity when dissolved.
  • B: Sodium chloride (NaCl) - Ionic compound, conducts electricity when dissolved.
  • C: Sugar (C12H22O11) - Non-ionic, does not conduct electricity.
  • D: Sodium hydroxide (NaOH) - Ionic compound, conducts electricity when dissolved.

⚡ Mnemonic / Speed-Run

Remember: "Ionic compounds conduct; covalent compounds don’t." This can help distinguish between conductors and insulators in solution.

6. Visual Suggestion

6. Visual Suggestion

Illustrate a setup comparing the conductivity of solutions: use a light bulb or voltmeter connected to two electrodes immersed in each solution (sugar, NaCl, CuSO4), showing that only ionic solutions light up.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Chemistry, Chapter on Solutions.

Question 2 of 10 Authentic UPSC NDA Question

Which one among the following is present inthe nettle leaf hairs that causes burning pain?

Step-by-Step Logic & Solution

Correct Answer

✓ Option A is correct. Methanoic acid is responsible for the burning pain caused by nettle hairs.

📖 Governing Law / Core Concept

The pain induced by nettle hairs is primarily due to the presence of methanoic acid (formic acid), with the molecular formula \( HCOOH \).

🧪 Step-by-Step Breakdown

Methanoic acid is released when the hair-like structures of the nettle plant penetrate the skin, resulting in a burning sensation.

\[ HCOOH \rightarrow H^+ + HCOO^- \]

As it dissociates in aqueous solution, it produces hydrogen ions (\( H^+ \)), which stimulate pain receptors in the skin.

🔍 Option Analysis

  • Option B: Ethanoic acid (acetic acid) is used in vinegar, but is not present in nettle.
  • Option C: Benzoic acid is used as a preservative and is not related to nettle stings.
  • Option D: Acetic acid (same as Ethanoic acid) doesn't cause the sting from nettles.

⚡ Mnemonic / Speed-Run

Remember "Methan- for the sting!" which links methanoic acid (formic acid) to its irritant effect.

6. Visual Suggestion

6. Visual Suggestion

A diagram showing a cross-section of a nettle leaf, highlighting the stinging hairs and the release of methanoic acid when the hair penetrates the skin.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Chemistry, Chapter on Carboxylic Acids.

Question 3 of 10 Authentic UPSC NDA Question

Which one among the following is known as Milk of Magnesia?

Step-by-Step Logic & Solution

Correct Answer

✓ Option D is correct. Milk of Magnesia is magnesium hydroxide.

📖 Governing Law / Core Concept

Milk of Magnesia, chemically known as magnesium hydroxide (\(Mg(OH)_2\)), functions as an antacid that neutralizes stomach acidity by the following reaction:

\[ Mg(OH)_2 + 2HCl \rightarrow MgCl_2 + 2H_2O \]

🧪 Step-by-Step Breakdown

Milk of Magnesia is a suspension of magnesium hydroxide in water. It acts as an antacid by reacting with hydrochloric acid present in the stomach, thereby reducing acidity.

Observation:

  • Appearance: White, milky solution.
  • pH Neutralization: Increases pH level, alleviating symptoms of indigestion.

🔍 Option Analysis

Other options consist of:

  • A: Magnesium bicarbonate - Exists in solution form but not as an antacid.
  • B: Magnesium carbonate - Used in different contexts, not a common antacid.
  • C: Magnesium sulphate - Known as Epsom salt, primarily used as a laxative.

⚡ Mnemonic / Speed-Run

Remember: "Milk of Magnesia = Magic for Your Stomach!"

6. Visual Suggestion

6. Visual Suggestion

A diagram illustrating the chemical structure of magnesium hydroxide along with its neutralization reaction with hydrochloric acid can enhance understanding.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Chemistry, Chapter on pH and its Applications.

Question 4 of 10 Authentic UPSC NDA Question

Which one of the following statements is NOT correct?

Step-by-Step Logic & Solution
✓

1. Correct Answer

Option B is correct. [The higher the hydrogen ion concentration in a solution, lower is its pH]

📖 Short Explanation

The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is inversely related to hydrogen ion concentration, meaning higher hydrogen ion concentration equates to a lower pH value.

💡 3. Why Correct Answer is Correct

The concept of pH is defined as the negative logarithm of the hydrogen ion concentration of a solution. Mathematically, it is expressed as:
\[ \text{pH} = -\log_{10}[\text{H}^+]\]
Here, a higher concentration of H+ ions indicates a lower pH, confirming that pH is inversely related to hydrogen ion concentration.

❌ 4. Why Other Options are Wrong

  • •Option A: Correct as it describes the pH scale accurately.
  • •Option C: Correct since the pH scale ranges from 0 to 14.
  • •Option D: Correct as 'p' in pH does stand for 'potenz.'
⚡

NDA Speed-Run / Mnemonic Shortcut

Remember that as pH decreases by 1, the H+ concentration increases by a factor of 10. Hence, low pH means high acidity.

🎯

5. Key Learning Point

pH is inversely related to H+ concentration: higher H+ means lower pH.

6. Visual Suggestion

A representative diagram showing a graduated pH scale ranging from 0 to 14, with annotations indicating low pH corresponds to high hydrogen ion concentration and vice versa, which could be accompanied by example acids and bases.

Question 5 of 10 Authentic UPSC NDA Question

For acid rain, the pH of rain water should be less than

Step-by-Step Logic & Solution
✓

1. Correct Answer

Option C is correct. For acid rain, the pH of rainwater must be less than 5.6.

📖 Short Explanation

Acid rain occurs when the pH of rainwater falls below 5.6, usually due to atmospheric pollutants like sulfur dioxide and nitrogen oxides reacting with water vapor to form acids.

💡 3. Why Correct Answer is Correct

The pH value is a measure of how acidic or basic a solution is. Pure water has a neutral pH of 7.0. Naturally occurring carbon dioxide in the atmosphere dissolves in rainwater, forming carbonic acid, which gives the rain a slightly acidic pH of about 5.6. However, when pollutants like sulfur dioxide and nitrogen oxides, often resulting from industrial emissions, combine with atmospheric moisture, they form sulfuric and nitric acids, respectively. This results in a lower pH level in rainwater, leading to acid rain when the pH falls below 5.6. Acid rain can have severe environmental consequences on soil, plants, aquatic systems, and infrastructure.

❌ 4. Why Other Options are Wrong

  • •Option A: pH 7.0 indicates neutrality, which is typical for pure water without any acidity.
  • •Option B: pH 6.6 is less acidic than rain with dissolved atmospheric CO2; hence, it is incorrect for acid rain, though it is closer.
  • •Option D: pH 8.0 is alkaline, not acidic, and cannot pertain to acid rain.
⚡

NDA Speed-Run / Mnemonic Shortcut

Remember 'Acid < 5.6' as a quick check for acidic environments linked to acid rain by associating the numerical value 5.6 with easy mnemonic phrases like "Acid is below 5.6, not above or even at 6".

🎯

5. Key Learning Point

Acid rain is identified by a pH level of less than 5.6, indicating its formation from pollutants reacting with atmospheric moisture, which lowers the pH.

6. Visual Suggestion

Create a diagram showing a cross-section of the atmosphere including sources of sulfur dioxide and nitrogen oxides, their reactions in the atmosphere, leading to acid formation, and the resultant acid rain impacting the earth.

Question 6 of 10 Authentic UPSC NDA Question

Which one of the following acids is predominantly found in tomatoes?

Step-by-Step Logic & Solution

Correct Answer

✓ Option C is correct. Oxalic acid is the predominant acid found in tomatoes.

📖 Governing Law / Core Concept

Oxalic acid (\(C_2H_2O_4\)) is a naturally occurring dicarboxylic acid found in various plants as a method of regulating calcium levels within the plant. It acts as a metabolite.

🧪 Step-by-Step Breakdown

In tomatoes, oxalic acid contributes to the tart flavor and is a part of various metabolic pathways. When ingested, it can react with calcium ions to form calcium oxalate:

\[ C_2H_2O_4 + Ca^{2+} \rightarrow CaC_2O_4 \downarrow + 2H^+ \]

This leads to the formation of a precipitate (calcium oxalate), which may appear in various foods.

🔍 Option Analysis

A: Acetic acid, found in vinegar, primarily contributes to sourness but is not predominant in tomatoes.

B: Tartaric acid is associated with grapes and cream of tartar, not tomatoes.

D: Lactic acid is produced in fermented foods, like yogurt, and is not characteristic of tomatoes.

⚡ Mnemonic / Speed-Run

To remember the acids: A for Acetic (Vinegar), T for Tartaric (Grapes), O for Oxalic (Spinach, Tomatoes), L for Lactic (Dairy).

6. Visual Suggestion

6. Visual Suggestion

A comparison table showing the presence of various acids in different fruits and vegetables, emphasizing the relative content of oxalic acid in tomatoes.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Chemistry, Chapter on Organic Compounds.

Question 7 of 10 Authentic UPSC NDA Question

The pH value of Milk of Magnesia is approximately

Step-by-Step Logic & Solution

Correct Answer

✓ Option C is correct. Milk of Magnesia is a basic suspension.

📖 Governing Law / Core Concept

Milk of Magnesia primarily consists of magnesium hydroxide \((Mg(OH)_2)\), which is a weak base. Its pH typically ranges between 10 and 11.

🧪 Step-by-Step Breakdown

The pH scale measures the acidity or basicity of a solution, with values below 7 indicating acids, 7 indicating neutrality, and above 7 indicating bases. The reaction for magnesium hydroxide in water is: \[ Mg(OH)_2 (s) \leftrightarrow Mg^{2+} (aq) + 2 OH^- (aq) \] The production of hydroxide ions \((OH^-)\) increases the basicity of the solution, resulting in a pH value near 10. \[ \text{pH} = -\log [H^+] \] Given that the concentration of hydroxide ions is high, the resulting concentration of hydrogen ions \([H^+]\) is low, thereby confirming a basic pH.

🔍 Option Analysis

- **A: Zero** - This suggests a strong acid, which is not applicable here. - **B: 7** - Indicates neutrality, but Milk of Magnesia is basic. - **C: 10** - Correct, as this indicates a basic solution. - **D: 14** - This indicates a strong base, which does not align with the characteristics of Milk of Magnesia.

⚡ Mnemonic / Speed-Run

Remember that "Milk of Magnesia" = "Magnesium Hydroxide" = "Basic Solution" (pH around 10).

6. Visual Suggestion

6. Visual Suggestion

Consider a pH scale diagram highlighting Milk of Magnesia at pH 10, showing how it compares with neutral and acidic solutions.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Chemistry, Chapter on Acids, Bases, and Salts.

Question 8 of 10 Authentic UPSC NDA Question

Which one of the following is an organic acid ?

Step-by-Step Logic & Solution

Correct Answer

✓ Option C is correct. Acetic acid is the only organic acid among the options.

📖 Governing Law / Core Concept

Organic acids are typically characterized by the presence of a carboxyl group (-COOH) in their molecular structure. Acetic acid, or ethanoic acid, is one such acid.

🧪 Step-by-Step Breakdown

1. Hydrochloric acid (HCl): An inorganic strong acid.

2. Nitric acid (HNO₃): Another inorganic strong acid.

3. Acetic acid (CH₃COOH): An organic acid, derived from vinegar.

4. Sulphuric acid (H₂SO₄): A highly strong inorganic acid.

🔍 Option Analysis

  • Hydrochloric acid (A): Inorganic acid, significant in digestion.
  • Nitric acid (B): Inorganic, used in fertilizers.
  • Acetic acid (C): Organic acid, used in food preservation.
  • Sulphuric acid (D): Industrial inorganic acid, used in batteries.

⚡ Mnemonic / Speed-Run

To remember which acids are organic, recall "ACiD - Acetic is Chemical Derived," emphasizing that only acetic acid fits the organic category.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 11 Chemistry, Chapter on Organic Compounds.

Question 9 of 10 Authentic UPSC NDA Question

Which one of the following does not represent the salt, Calcium carbonate?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (a) is correct. Lime water does not represent calcium carbonate.

📖 Governing Law / Core Concept

Calcium carbonate (CaCO3) is a common substance found in rocks, and it comprises three well-known forms: limestone, chalk, and marble. Lime water is a saturated solution of calcium hydroxide (Ca(OH)2), not calcium carbonate.

🧪 Step-by-Step Breakdown

  • Lime Water: Solution of calcium hydroxide; formula: Ca(OH)2
  • Calcium Carbonate Types:
    • Limestone: Composed mainly of CaCO3
    • Chalk: Soft white limestone comprising CaCO3
    • Marble: Metamorphic rock originating from limestone, primarily CaCO3

🔍 Option Analysis

  • Option (b) Limestone: Composed of CaCO3, thus a representation.
  • Option (c) Chalk: A type of limestone, thus also CaCO3.
  • Option (d) Marble: Metamorphosed limestone, so composed of CaCO3.

⚡ Mnemonic / Speed-Run

Remember: "Lime is not a "carbonate" hero, Calcium Carbonate is championed by limestone, chalk, and marble."

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 10 Science, Chapter 2 (Acids, Bases, and Salts).

Question 10 of 10 Authentic UPSC NDA Question

Litmus, a well-known acid-base indicator, is derived from:

Step-by-Step Logic & Solution

Correct Answer

✓ Option B is correct. Litmus is derived from lichens.

📖 Governing Law / Core Concept

Litmus is a natural pH indicator obtained primarily from the lichen species Roccella tinctoria and Lecanora tartarea.

🧪 Step-by-Step Breakdown

Litmus undergoes color change upon reaction with acids and bases:

  • In acidic solutions (pH < 7): Litmus turns red.
  • In neutral solutions (pH = 7): Litmus remains purple.
  • In basic solutions (pH > 7): Litmus turns blue.

This color change occurs due to the protonation and deprotonation of the litmus dye, a complex mixture of various compounds providing these observable characteristics.

🔍 Option Analysis

  • A: Fungi - Incorrect; while lichens contain fungi, they are not derived solely from them.
  • C: Bacteria - Incorrect; litmus is not derived from bacterial sources.
  • D: Termite - Incorrect; termites do not produce litmus.

⚡ Mnemonic / Speed-Run

Remember: "Litmus Lichen - L for Lichen = Litmus!"

6. Visual Suggestion

6. Visual Suggestion

A pH scale diagram showing the color changes of litmus from red (in acidic) to blue (in basic) solutions, illustrating the transition points clearly for educational purposes.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Chemistry, Chapter 14 (Environmental Chemistry).

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