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Preparation and Properties of Hydrogen Questions

Chapter: Important Gases | Total Available: 17 Real Questions

Question 1 of 10 Authentic UPSC NDA Question

Which one of the following is the colour ofhydrogen gas?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (d) is correct. Hydrogen is a colourless gas.

📖 Governing Law / Core Concept

Hydrogen (H2) is the simplest and lightest element in the periodic table, and it is known for being colourless, odourless, and tasteless under standard conditions.

🧪 Step-by-Step Breakdown

As a diatomic molecule, hydrogen exists naturally as H2. The chemical reaction involved in its formation is:

\[ 2H_2(g) + O_2(g) \rightarrow 2H_2O(l) \, \text{(Combustion of hydrogen)}\]

During combustion, hydrogen reacts with oxygen, producing water, which is a colourless liquid. Observations using hydrogen in experiments show no visible colour change, confirming its colourless nature.

🔍 Option Analysis

  • A: Light yellow: Incorrect; hydrogen does not exhibit this colour.
  • B: Orange: Incorrect; hydrogen is not orange in any state.
  • C: Black: Incorrect; hydrogen cannot be black, as it is a gaseous element.

⚡ Mnemonic / Speed-Run

  • Remember: "Hydrogen is H2 - Colourless with no fuss!"

6. Visual Suggestion

6. Visual Suggestion

Consider a diagram showing a comparison of various gases, highlighting hydrogen as colourless, alongside gases that exhibit distinct colours.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 11 Chemistry, Chapter 5 (Classification of Elements and Periodicity in Properties).

Question 2 of 10 Authentic UPSC NDA Question

Which one of the following is termed as 'Dry ice'?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (c) is correct. Solid state of carbon dioxide is known as 'Dry ice'.

📖 Governing Law / Core Concept

Dry ice refers specifically to the solid form of carbon dioxide (CO2). At temperatures below -78.5°C, carbon dioxide can exist as a solid, sublimating directly from solid to gas without passing through a liquid phase.

🧪 Step-by-Step Breakdown

  • Dry ice is produced by compressing gaseous carbon dioxide into a liquid state, then allowing it to expand rapidly, which cools it substantially.
  • Upon solidification, it is white, opaque, and often used in refrigeration and as a cooling agent.
  • Sublimation occurs, whereby dry ice changes directly to carbon dioxide gas, absorbing heat from its surroundings, hence creating a cooling effect.

🔍 Option Analysis

  • A: Ice present in ice-cream refers to frozen water and is not related to carbon dioxide.
  • B: Solid water at Antarctica generally refers to ice or glaciers, not CO2.
  • D: Solid water of ionosphere is misleading, as the ionosphere comprises charged particles, not solid water.

⚡ Mnemonic / Speed-Run

Remember "Dry Ice = CO2 Freeze" to recall that dry ice is the frozen state of carbon dioxide.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Chemistry, Chapter on States of Matter.

Question 3 of 10 Authentic UPSC NDA Question

Which one of the following will NOT produce carbon dioxide on reacting with an aqueous solution of hydrochloric acid ?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (b) is correct. Quick Lime does not produce carbon dioxide with hydrochloric acid.

📖 Governing Law / Core Concept

The reaction of acids with carbonates and bicarbonates generally results in the production of carbon dioxide. The fundamental reaction can be represented as follows:

\[ \text{CaCO}_3 + 2 \text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O} \]

🧪 Step-by-Step Breakdown

Let's analyze the options:

  • A: Limestone (CaCO3) - Reacts with HCl:
    • \[ \text{CaCO}_3 + 2 \text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O} \]
  • C: Chalk (CaCO3) - Identical to Limestone:
    • \[ \text{CaCO}_3 + 2 \text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O} \]
  • D: Marble (CaCO3) - Again, behaves like Limestone:
    • \[ \text{CaCO}_3 + 2 \text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O} \]
  • B: Quick Lime (CaO) - Does not contain carbonate.
    • \[ \text{CaO} + 2 \text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} \]

🔍 Option Analysis

  • A: Limestone - Produces CO2.
  • B: Quick Lime - Does not produce CO2.
  • C: Chalk - Produces CO2.
  • D: Marble - Produces CO2.

⚡ Mnemonic / Speed-Run

Remember that substances containing carbonate (CaCO3) will produce carbon dioxide upon reaction with hydrochloric acid.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

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

Question 4 of 10 Authentic UPSC NDA Question

 Dinitrogen (N₂) and dioxygen (O₂) are the main constituents of air but they do not react with each other to form oxides of nitrogen because

Step-by-Step Logic & Solution

Correct Answer

✓ Option (c) is correct. The reaction is endothermic and requires very high temperature.

📖 Governing Law / Core Concept

The reaction between dinitrogen (\(N_2\)) and dioxygen (\(O_2\)) to form nitric oxides (\(NO\) or \(NO_2\)) is represented as:

\[N_2 + O_2 \xrightarrow{\text{High Temp}} 2NO\]

This reaction is endothermic, requiring energy input to proceed.

🧪 Step-by-Step Breakdown

The reaction proceeds at high temperatures, such as in combustion engines or lightning strikes, where the energy is sufficient to break the strong triple bond in \(N_2\).

  • The bond dissociation energy of \(N \equiv N\) is approximately 941 kJ/mol.
  • Activation energy must be provided to initiate the reaction.
  • Without the necessary temperature, \(N_2\) and \(O_2\) remain inert.

🔍 Option Analysis

  • A: The reaction does require a catalyst, but the primary barrier is temperature.
  • B: Oxides of nitrogen can be stable under specific conditions; they do not intrinsically exhibit instability.
  • D: The air composition does not hinder the reaction specifically; rather, lack of adequate energy is the issue.

⚡ Mnemonic / Speed-Run

Remember: "High Energy = Reactivity" to recall that nitrogen and oxygen need significant energy to react.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Chemistry, Chapter on Chemical Thermodynamics and Kinetics.

Question 5 of 10 Authentic UPSC NDA Question

 What is the colour of the precipitate obtained by passing CO₂ gas through lime water?

Step-by-Step Logic & Solution

Correct Answer

✓ Option C is correct. The precipitate formed is white.

📖 Governing Law / Core Concept

The reaction involves the formation of calcium carbonate from carbon dioxide and calcium hydroxide. The reaction can be classified as a precipitation reaction.

🧪 Step-by-Step Breakdown

The chemical reaction of passing CO₂ through lime water (calcium hydroxide solution) is as follows:

\[ \text{Ca(OH)}_2 (aq) + \text{CO}_2 (g) \rightarrow \text{CaCO}_3 (s) + \text{H}_2\text{O} (l) \]

Here, calcium carbonate \((\text{CaCO}_3)\) is formed as a precipitate, which appears white in color.

🔍 Option Analysis

Other options include

  • A: Green - Not applicable, as no green compounds are formed.
  • B: Blue - Incorrect, no blue precipitate is created in this reaction.
  • D: Brown - No browning occurs; the precipitate is distinctly white.

⚡ Mnemonic / Speed-Run

Remember: CO₂ + Ca(OH)₂ gives you "C" for "Calcium" followed by "W" for "White" (CaCO₃ precipitate).

6. Visual Suggestion

6. Visual Suggestion

A diagram demonstrating the reaction setup: a flask with lime water, CO₂ gas input, and the resulting white precipitation of CaCO₃. This could show before and after states for clarity.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 12 Chemistry, Chapter 1 (Some Basic Concepts of Chemistry).

Question 6 of 10 Authentic UPSC NDA Question

Which one of the following statements about dihydrogen (H₂) is not correct?

Step-by-Step Logic & Solution

Correct Answer

✓ Option D is correct. A mixture of NO₂ and H₂ is not known as Syngas.

📖 Governing Law / Core Concept

Dihydrogen (H₂) is a diatomic molecule known for its reactivity and role in various chemical reactions. The term "Syngas" refers to a mixture of carbon monoxide (CO) and hydrogen (H₂) typically produced by gasifying carbon-containing materials.

🧪 Step-by-Step Breakdown

- Dihydrogen (H₂) reacts with oxygen (O₂) to form water:
\[ 2H_2 + O_2 \rightarrow 2H_2O \]
- Hydrogen does react with alkali metals (e.g., sodium) to form metal hydrides (e.g., NaH) at high temperatures:
\[ 2Na + H_2 \rightarrow 2NaH \]

🔍 Option Analysis

- **Option A**: H₂ is indeed lighter than air and almost insoluble in water, correct. - **Option B**: H₂ is relatively inert under standard conditions due to the strong H-H bond. - **Option C**: H₂ does react with metals, forming hydrides at elevated temperatures.

⚡ Mnemonic / Speed-Run

Mnemonic for Syngas components: **"Carbon Over Hydrogen makes Syngas"** (to remember CO + H₂).

6. Visual Suggestion

6. Visual Suggestion

Diagram comparing Syngas components: CO vs NO₂ + H₂, highlighting production methods and reactions involved.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Chemistry, Chapter on Hydrogen and its Compounds.

Question 7 of 10 Authentic UPSC NDA Question

Which one of the following is known as ‘water gas’?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (d) is correct. Water gas is a mixture of carbon monoxide and hydrogen gas.

📖 Governing Law / Core Concept

Water gas is primarily produced via the reaction of solid carbon with water vapor. This process can be represented by the following reaction:

\[ C(s) + H_2O(g) \rightarrow CO(g) + H_2(g) \]

🧪 Step-by-Step Breakdown

The reaction occurs at high temperatures (around 1270 K), where the steam reacts with solid carbon (usually sourced from coke), forming a gaseous mixture of carbon monoxide (CO) and hydrogen (H₂). This mixture, known as water gas, is utilized in various industrial processes, including:

  • Synthesis of methanol
  • Production of hydrocarbons

Water gas plays a crucial role in chemical industries due to its reactivity and ability to serve as a reducing agent.

🔍 Option Analysis

  • A: H₂O + CO₂ - Not a known gas; refers to water and carbon dioxide.
  • B: NH₃ - Ammonia, a different compound not related to water gas.
  • C: H₂ + N₂ - A mixture of hydrogen and nitrogen gases, not specific to water gas.

⚡ Mnemonic / Speed-Run

Remember: Carbon + H₂O = CO + H₂ (Water Gas) can be simplified to "C-H to C-O & H".

6. Visual Suggestion

6. Visual Suggestion

Illustrate the water gas production process in a flow chart showing solid carbon reacting with steam at high temperature to form water gas (CO + H₂). Include arrows indicating the reaction direction and label reactants and products.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Chemistry, Chapter on Hydrocarbons.

Question 8 of 10 Authentic UPSC NDA Question

Which one of the following nitrogen oxides may dimerise?

Step-by-Step Logic & Solution
✓

1. Correct Answer

Option B is correct. NO2 is the nitrogen oxide that may dimerise.

📖 Core Concept

NO2 can form a dimer due to its unpaired electron, allowing it to combine with another NO2 molecule to form N2O4.

💡 3. Explanation

NO2 is a nitrogen dioxide molecule featuring an unpaired electron, which makes it paramagnetic. This unpaired electron allows interaction with another NO2 molecule to form a stable dimer, specifically N2O4, through the reaction:
2 NO2 ⇌ N2O4
This dimerization process stabilizes the odd electron condition by forming a diamagnetic compound, where electrons are paired.

❌ 4. Option Analysis

  • •Option A: N2O (Nitrous oxide) does not have unpaired electrons and is stable, therefore it does not dimerize.
  • •Option C: N2O3 (Dinitrogen trioxide) is a balanced stable compound that does not dimerize.
  • •Option D: N2O5 (Dinitrogen pentoxide) is robust against dimerization under standard conditions.
⚡

NDA Speed-Run / Mnemonic Shortcut

Remember that molecules containing an odd electron, like NO2, often form dimers to stabilize via electron pairing.

🎯

5. Key Takeaways

Nitrogen oxides with odd unpaired electrons, like NO2, have a tendency to form dimers (N2O4).

6. Visual Suggestion

Visual representation can include Lewis structures of NO2 displaying the unpaired electron and the resultant N2O4 dimer showing paired electrons, highlighting the dimerization process effectively.

Question 9 of 10 Authentic UPSC NDA Question

Match List-I with List-II and select the answerusing the code given below the lists :

Step-by-Step Logic & Solution
✓

1. Correct Answer

Option D is correct. Washing soda is Na2CO3 • 10H2O, Baking soda is NaHCO3, Bleaching powder is CaOCl2, and Gypsum is CaSO4 • 2H2O.

📖 Short Explanation

The question requires matching chemical names with their respective chemical formulas. Familiarity with common chemical compounds and their systematic naming conventions aids in selecting the correct match.

💡 3. Why Correct Answer is Correct

Understanding the relationships between common chemical names and their formulas is crucial. Here's a detailed breakdown of the matches:

  • Washing Soda: Na2CO3 • 10H2O is consistent with the definition of washing soda, which is sodium carbonate decahydrate.
  • Baking Soda: NaHCO3 is baking soda, scientifically known as sodium bicarbonate.
  • Bleaching Powder: CaOCl2 is calcium hypochlorite, commonly referred to as bleaching powder.
  • Gypsum: CaSO4 • 2H2O is hydrated calcium sulfate, known as gypsum.

❌ 4. Why Other Options are Wrong

  • •Option A: Incorrect matches do not align with the standard chemical names and formulas.
  • •Option B: Incorrect pairings reveal mismatches in formula assignments.
  • •Option C: While some matches may be tempting, incorrect pairings invalidate this option.
⚡

NDA Speed-Run / Mnemonic Shortcut

Remember the key components: Sodium carbonate is washing soda, sodium bicarbonate is baking soda, and calcium hypochlorite is bleaching powder. For gypsum, think of drywall and its hydration.

🎯

5. Key Learning Point

Understanding the relationship between common product names and their chemical compositions is essential for identifying correct chemical formulas.

6. Visual Suggestion

A visual chart depicting common household chemicals, their chemical formulas, and uses can help memorize these associations effectively.

Question 10 of 10 Authentic UPSC NDA Question

Which one of the following is also known as dry ice in its solid form?

Step-by-Step Logic & Solution
✓

1. Correct Answer

Option B is correct. Dry ice is the solid form of carbon dioxide (CO2).

📖 Short Explanation

Dry ice is the common name for solid carbon dioxide (CO2). It is used primarily as a cooling agent and is known for its ability to sublimate, transitioning from a solid to a gas without passing through a liquid phase.

💡 3. Why Correct Answer is Correct

Dry ice, which is solid carbon dioxide, is utilized in various industrial and scientific applications due to its properties. Unlike water ice, which melts into liquid water, dry ice sublimates directly from a solid to a gas. This occurs at temperatures below −78.5 °C (−109.3 °F) and is beneficial for refrigeration purposes where moisture is undesirable.
CO2(s) → CO2(g)

❌ 4. Why Other Options are Wrong

  • •Option A: SiO2 refers to silicon dioxide, also known as silica, which is a chemical compound found in sand and quartz. It is not related to dry ice.
  • •Option C: CaO, or calcium oxide, is commonly known as quicklime or lime. This substance is used in building materials, not as dry ice.
  • •Option D: MgO stands for magnesium oxide, which is a white hygroscopic solid often used in medical applications or materials. It has no relation to dry ice.
⚡

NDA Speed-Run / Mnemonic Shortcut

To remember that dry ice is solid carbon dioxide, recall the mnemonic "D CO2," where "D" stands for dry and "CO2" is the chemical formula for carbon dioxide.

🎯

5. Key Learning Point

Dry ice is unique because it sublimates directly into carbon dioxide gas, avoiding the liquid phase entirely. This property is crucial for its use as a cooling agent.

6. Visual Suggestion

A diagrammatic representation showing a block of dry ice (CO2 solid) sublimating into carbon dioxide gas (CO2 gas) can help visualize the transition. Additionally, a temperature scale highlighting the point of sublimation at -78.5 °C will reinforce understanding.

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