Preparation and Properties of Carbon Dioxide

Correct Answer

📖 Governing Law / Core Concept

Biogas is primarily composed of methane (CH₄) and carbon dioxide (CO₂), generated through anaerobic digestion of organic matter.

🧪 Step-by-Step Breakdown

The production of biogas can be represented by the following reaction:

During this process, for every mole of organic matter, methane is generated as the main product:

Typical biogas composition is as follows:

• Methane (CH₄): 50-75%
• Carbon Dioxide (CO₂): 25-50%
• Hydrogen (H₂): 0-1%
• Hydrogen Sulphide (H₂S): < 1%

🔍 Option Analysis

Other options consist of:

• Carbon Dioxide (A): Major component but not as much as methane.
• Hydrogen (C): Minimal presence in biogas.
• Hydrogen Sulphide (D): Trace amounts, primarily a contaminant.

⚡ Mnemonic / Speed-Run

Remember this for biogas components: "Methane Might Command": Methane (75%) > Carbon Dioxide (50%) > Hydrogen (1%) > Hydrogen Sulfide (trace).

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

The decomposition of sodium bicarbonate (\( \text{NaHCO}_3 \)) upon heating is an example of thermal decomposition, where a single compound breaks down into two or more products.

🧪 Step-by-Step Breakdown

Upon heating, sodium bicarbonate decomposes as follows: This reaction produces sodium carbonate (\( \text{Na}_2\text{CO}_3 \)), water vapor (\( \text{H}_2\text{O} \)), and carbon dioxide (\( \text{CO}_2 \)). The gas released (carbon dioxide) is what makes baked goods rise.

🔍 Option Analysis

• B: Hydrogen - Not produced in this reaction.
• C: Water vapour - Produced, but not the primary product that causes leavening.
• D: Oxygen - Not involved in the decomposition of sodium bicarbonate.

⚡ Mnemonic / Speed-Run

Remember the decomposition of bicarbonate results in gas release: "Baking with Bicarb Makes Bubbles" (where bubbles refer to carbon dioxide).

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 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:

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

📖 Factual Verification & Reference

Correct Answer

📖 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:

🧪 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