Properties of Air and Water Questions

Correct Answer

📖 Governing Law / Core Concept

The reactivity of metals with water follows a specific order, defined by their position in the reactivity series, which ranks metals based on their ability to displace hydrogen from water and form hydroxides.

🧪 Step-by-Step Breakdown

Metals react with water producing hydroxides and hydrogen gas. The general reaction is:

For example, when Zinc reacts with water, the reaction is as follows:

This illustrates that Zinc can react with water, but Copper cannot react under normal conditions. Iron and Lead have lesser reactivity compared to Zinc when discussing water displacement.

🔍 Option Analysis

• Option B: Incorrect. Copper is least reactive and does not effectively displace hydrogen from water.
• Option C: Incorrect. While Copper is less reactive than Zinc, it cannot displace hydrogen from water.
• Option D: Incorrect. It misplaces Copper’s position in the reactivity series.

⚡ Mnemonic / Speed-Run

For remembering the reactivity series with water, use the mnemonic: “Please Send My Cat Home” for Potassium, Sodium, Magnesium, Calcium, and then Iron, Zinc, Lead, and Copper.

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

Water (H₂O) is a polar molecule because of its bent shape and the difference in electronegativity between hydrogen and oxygen, leading to a permanent dipole moment.

🧪 Step-by-Step Breakdown

In water:

• Hydrogen bonds form between water molecules due to polarity.
• Water has a high boiling point (100°C) compared to other molecules of similar size due to hydrogen bonding.
• It has a high heat of fusion (334 J/g) because of the energy required to break these hydrogen bonds when freezing occurs.

🔍 Option Analysis

• A: True, hydrogen bonds are present in liquid water.
• B: True, water has a high boiling point.
• C: True, water has a high heat of fusion.
• D: False, water is a polar molecule.

⚡ Mnemonic / Speed-Run

Remember, "Water is Polar" to recall its molecular structure and properties related to hydrogen bonding.

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

Metals react with water based on their position in the reactivity series. Metals like potassium and sodium are more reactive than magnesium and readily react with cold water.

🧪 Step-by-Step Breakdown

Reactivity towards water can be summarized as:

• Metals such as potassium (K) and sodium (Na) react vigorously with cold water:
\[ 2K + 2H_2O \rightarrow 2KOH + H_2 \]
\[ 2Na + 2H_2O \rightarrow 2NaOH + H_2 \]
• Calcium (Ca) also reacts, albeit less violently:
\[ Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2 \]
• Magnesium (Mg), however, does not react with cold water but will react with hot water or steam:
\[ Mg + H_2O_{(steam)} \rightarrow MgO + H_2 \]

🔍 Option Analysis

A brief review of the other options:

• A: Calcium (Ca) - Reacts with cold water.
• B: Potassium (K) - Reacts violently with cold water.
• D: Sodium (Na) - Reacts vigorously with cold water.

⚡ Mnemonic / Speed-Run

Remember: "King Size Noodles Can" - K (Potassium) and Na (Sodium) react; Mg (Magnesium) does not.

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

The physical properties of elements are influenced by their molecular structure and intermolecular forces. At normal room temperature (25°C) and pressure (1 atm), Mercury (Hg) and Bromine (Br₂) remain in liquid state due to their unique physical properties.

🧪 Step-by-Step Breakdown

Mercury is a heavy metal, a dense liquid at room temperature, characterized by a melting point of -38.83°C. Meanwhile, Bromine, a halogen, is a reddish-brown liquid which melts at -7.2°C. Both substances remain liquid under typical atmospheric conditions.

🔍 Option Analysis

- **Option (a) Gallium and Bromine**: Gallium solidifies at 29.76°C. Only Bromine remains liquid.
- **Option (c) Gallium and Mercury**: Both exhibit different states at room temperature; Gallium is solid.
- **Option (d) Gallium and Caesium**: Caesium is solid at room temperature.

⚡ Mnemonic / Speed-Run

Remember the mnemonic: "Mercury-Bromine, Liquid Team!" Both are the only liquid pair at room temperature.

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

The chemical formula of Ferrous Sulphate heptahydrate is \( \text{FeSO}_4 \cdot 7\text{H}_2\text{O} \), indicating it includes seven molecules of water.

🧪 Step-by-Step Breakdown

The presence of water of crystallization defines the hydration state of a salt, impacting its properties: The green vitriol's color arises from hydrated ferrous ions, which influences applications in agriculture and analytical chemistry.

🔍 Option Analysis

- **A: 1** - Incorrect; does not represent the total water of crystallization. - **B: 3** - Incorrect; lesser than the actual count in heptahydrate. - **C: 5** - Incorrect; not the complete hydration for Ferrous Sulphate.

⚡ Mnemonic / Speed-Run

Remember "Hepta = 7" to link the number seven in 'heptahydrate' to the seven water molecules.

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

The definition of hydrolysis involves the chemical breakdown of compounds by reaction with water. In minerals, it often results in the alteration of their chemical structure.

🧪 Step-by-Step Breakdown

The process of hydrolysis encompasses reactions such as: \[ \text{Mineral (e.g., Feldspar)} + \text{H}_2\text{O} \rightarrow \text{Clay} + \text{Dissolved Ions} \] In the example of feldspar (\(KAlSi_3O_8\)): \[ 2KAlSi_3O_8 + 11H_2O + 2H^+ \rightarrow Al_2Si_2O_5(OH)_4 + 4SiO_2 + 2K^+ \] Observation indicates that minerals undergo physical and chemical changes, expanding due to absorbed water causing stresses, common in geological processes.

🔍 Option Analysis

- **A: Hydration** refers to the incorporation of water into the crystal structure without significant change in chemical composition. - **B: Oxidation** is a process where a substance loses electrons, often affecting metal reactivity but is not directly related to mineral expansion. - **D: Carbonation** involves the reaction of minerals with carbon dioxide and water, forming carbonates but does not primarily relate to absorption and expansion.

⚡ Mnemonic / Speed-Run

**Remember Hydrolysis**: "Hydro" means water, "lysis" means to break down – breaking minerals with water!

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

The density of water varies with temperature, governed by its unique molecular structure and hydrogen bonding properties. The maximum density of water is observed at 4°C, where it achieves a density of 1 g/cm³ or 1000 kg/m³.

🧪 Step-by-Step Breakdown

At different temperatures, the density of water is influenced by molecular motion:

• At 0°C, density is approximately 999.84 kg/m³.
• At 4°C, density reaches its peak at 1000 kg/m³.
• At temperatures above or below 4°C, water exhibits lower density.

Thus, the correct option highlights the maximum density value:

🔍 Option Analysis

• Option (b): Incorrect. Density at 0°C is indeed slightly less than 1000 kg/m³.
• Option (c): Incorrect. Density is not 100 kg/m³, misrepresenting the values.
• Option (d): Incorrect. Density is far greater than 10 kg/m³.

⚡ Mnemonic / Speed-Run

Recall: "Water Peaked at Four" - Remembering that water's maximum density is at 4°C aids in answering related questions accurately.

📊 Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

Temporary hardness of water results primarily from the presence of bicarbonates of calcium (Ca(HCO₃)₂) and magnesium (Mg(HCO₃)₂). The reaction leading to temporary hardness can be represented as:

🧪 Step-by-Step Breakdown

The presence of bicarbonates leads to formation of precipitates when heated:

The observations during these reactions include cloudiness due to carbonate precipitation, typically manifested as a whitish precipitate.

🔍 Option Analysis

• A: Sulphates of calcium - Leads to permanent hardness, as it does not precipitate on boiling.
• B: Chlorides of magnesium - Contributes to permanent hardness, remains soluble after heating.
• D: Sulphates of magnesium - Represents permanent hardness, similar to chlorides, unaffected by boiling.

⚡ Mnemonic / Speed-Run

Remember: “Bicarbonate is temporary, Sulphate is forever.” This can help to quickly recall that bicarbonates cause temporary hardness.

6. Visual Suggestion

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

Pure water is defined as a compound consisting solely of H₂O molecules, devoid of contaminants, minerals, or impurities.

🧪 Step-by-Step Breakdown

Rainwater originates from the condensation of water vapor in the atmosphere, undergoing a process of distillation. This process generally yields a high purity level, since:

• It is free from dissolved salts and pollutants present in rivers, seas, and wells.
• Evaporation leaves behind impurities, while rainwater condenses into clouds and later falls as clean precipitation.

🔍 Option Analysis

A: River water: Contains many impurities, including organic matter and pollutants.
B: Sea water: High salinity (approx. 35 g/L) and contains various marine pollutants.
C: Well water: May contain minerals and contaminants, depending on geological formations and depth.

⚡ Mnemonic / Speed-Run

Recall this: "Raining is Pure" to remember that rainwater is often the purest source of water available naturally.

📖 Factual Verification & Reference

Correct Answer

📖 Governing Law / Core Concept

Water of crystallization refers to the specific number of water molecules that are chemically bound to a crystalline compound, which is crucial in defining salts' hydration states.

🧪 Step-by-Step Breakdown

The correct molecular formula for Plaster of Paris is:

In contrast, gypsum, which has a molecular formula of:

shows differences in dehydration properties and usage in construction and other applications.

🔍 Option Analysis

• A: Correct. Water of crystallization is defined accurately.
• C: Correct. Washing soda (Na₂CO₃·10H₂O) indeed removes permanent hardness through precipitation of calcium and magnesium ions.
• D: Correct. The atmosphere of Venus is primarily composed of thick sulfuric acid clouds, with significant greenhouse gas effects.

⚡ Mnemonic / Speed-Run

Mnemonic for remembering water of crystallization: "Gypsum is two, Plaster is half true!"

6. Visual Suggestion

📖 Factual Verification & Reference