General Principles and Processes of Isolation of Elements Previous Year Questions — JEE Main Chemistry
4 past-year General Principles and Processes of Isolation of Elements questions from JEE Main (Chemistry).
Q38 (2025)
Given below are two statements:
Statement I: Wet cotton clothes made of cellulose based carbohydrate takes comparatively longer time to get dried than wet nylon polymer based clothes.
Statement II: Intermolecular hydrogen bonding with water molecule is more in nylon-based clothes than in the case of cotton clothes.
In the light of above statements, choose the correct answer from the options given below :
- Statement I is false but Statement II is true
- Statement I is true but Statement II is false
- Both Statement I and Statement II are true
- Both Statement I and Statement II are false
### Related Formula
Hydrogen bonding affinity:
$$\text{Affinity for water} \propto \text{Density of accessible hydroxyl groups (-OH)}$$
### Core Logic
Statement I Analysis:
- Cotton is made of cellulose, which possesses a high density of free hydroxyl ($-OH$) groups per monomer unit. These groups form strong intermolecular hydrogen bonds with water molecules, holding moisture tightly. Nylon is a synthetic polyamide with much lower hydrogen bonding affinity for water. Thus, cotton clothes retain water longer and dry slower than nylon clothes. Statement I is True.
### Step 1: Analyze Statement II
- Statement II claims that hydrogen bonding with water is stronger in nylon than in cotton. This is False because cellulose (cotton) contains a much higher density of active hydrophilic hydroxyl ($-OH$) groups compared to the amide groups in nylon, which are often engaged in intramolecular crystalline structures within the polymer itself.
### Step 2: Conclusion
Therefore, Statement I is True but Statement II is False, matching Option (2).
### Pattern Recognition
Natural fibers like cotton (cellulose) are highly hydrophilic due to the presence of multiple hydroxyl groups per glucose unit, leading to high water absorption and slower drying. Synthetic fibers like nylon are hydrophobic by comparison, leading to minimal absorption and rapid drying.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 12 Chemistry: Polymers
Class 12 Chemistry: Biomolecules
Q1662 (2024)
Identify the incorrect pair from the following :
- $\text{Fluorspar- } BF_3$
- $\text{Cryolite- } Na_3AlF_6$
- $\text{Fluoroapatite- } 3Ca_3(PO_4)_2.CaF_2$
- $\text{Carnallite- } KCl.MgCl_2.6H_2O$
### Core Logic
Let's check the mineral formulas assigned to common names:
1. Fluorspar: The formula for fluorspar (also known as fluorite) is $CaF_2$, not $BF_3$. This pair is incorrect.
2. Cryolite: Correctly given as $Na_3AlF_6$.
3. Fluoroapatite: Correctly given as $3Ca_3(PO_4)_2 \cdot CaF_2$ (or $Ca_5(PO_4)_3F$).
4. Carnallite: Correctly given as $KCl \cdot MgCl_2 \cdot 6H_2O$.
### Step 1: Final Conclusion
The incorrect pair is option 1.
{{SOL_IMG1}}
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 12 Chemistry: General Principles and Processes of Isolation of Elements
Class 11 Chemistry: The p Block Elements
Q88 (2024)
Number of metal ions characterized by flame test among the following is
$$Sr^{2+}, Ba^{2+}, Ca^{2+}, Cu^{2+}, Zn^{2+}, Co^{2+}, Fe^{2+}$$
### Core Logic
The flame test is typically used to characterize certain s-block metals (like alkali and alkaline earth metals) and a few transition metals that impart characteristic colors to a Bunsen flame.
Evaluating the given ions:
1. $Sr^{2+}$: Crimson red flame. (Yes)
2. $Ba^{2+}$: Apple green flame. (Yes)
3. $Ca^{2+}$: Brick red flame. (Yes)
4. $Cu^{2+}$: Blue-green flame. (Yes)
5. $Zn^{2+}$: No characteristic flame color in standard qualitative analysis. (No)
6. $Co^{2+}$: No characteristic flame color. (No)
7. $Fe^{2+}$: No characteristic flame color. (No)
### Step 1: Final Count
The metal ions characterized by flame tests are $Sr^{2+}, Ba^{2+}, Ca^{2+}$, and $Cu^{2+}$.
Total number = 4.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 11 Chemistry: The s Block Elements
Class 12 Chemistry: The d and f Block Elements
Q88 (2024)
The values of conductivity of some materials at $298.15\text{ K}$ in $\text{S m}^{-1}$ are $2.1 \times 10^3, 1.0 \times 10^{-16}, 1.2 \times 10, 3.91, 1.5 \times 10^{-2}, 1 \times 10^{-7}, 1.0 \times 10^3$. The number of conductors among the materials is ________
### Core Logic
Materials are classified based on their electrical conductivity at room temperature:
- Conductors: Conductivity range is generally between $10^4$ to $10^7\text{ S m}^{-1}$ for metals, but aqueous electrolytes and certain semi-metals fall in the intermediate $1$ to $10^3\text{ S m}^{-1}$ range broadly qualifying as conductors in the context of typical chemical classifications.
- Semiconductors: $10^{-6}$ to $10^4\text{ S m}^{-1}$
- Insulators: $10^{-20}$ to $10^{-10}\text{ S m}^{-1}$
Wait, typical values for metallic conductors are high, but comparing them strictly against the NCERT table:
$2.1 \times 10^3$ (Conductor)
$1.2 \times 10$ (Conductor)
$3.91$ (Conductor)
$1.0 \times 10^3$ (Conductor)
$1.0 \times 10^{-16}$ (Insulator)
$1.5 \times 10^{-2}$ (Semiconductor)
$1.0 \times 10^{-7}$ (Semiconductor / Insulator)
### Step 1: Final Counting
The materials with conductivities $2.1 \times 10^3$, $1.2 \times 10$, $3.91$, and $1.0 \times 10^3$ fall into the category of conductors.
Therefore, the number of conductors is $4$.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 12 Chemistry: Solid State
Class 12 Chemistry: Electrochemistry
