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Chemistry

Everyday Examples

Chapter: Acids, Bases, and Salts

Question 1 of 5 NDA MCQ

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

Detailed Explanation

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 5 NDA MCQ

Which one of the following is an organic acid ?

Detailed Explanation

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 3 of 5 NDA MCQ

The pH value of Milk of Magnesia is approximately

Detailed Explanation

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 4 of 5 NDA MCQ

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

Detailed Explanation

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 5 of 5 NDA MCQ

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

Detailed Explanation
✓

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.

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