Some Basic Concepts of Chemistry - NEET PYQs (2009-2024)

🎯 Overview

Welcome to the comprehensive collection of NEET Previous Year Questions on “Some Basic Concepts of Chemistry” from 2009-2024. This fundamental chapter forms the foundation of Physical Chemistry and consistently appears with 2-3 questions every year, primarily focusing on numerical problems related to mole concept, stoichiometry, and concentration terms.

📊 Chapter Analysis & Statistics

Question Distribution

📈 PYQ Distribution (2009-2024):
- Total Questions: 45-55 questions
- Average per year: 3-4 questions
- Difficulty Level: Easy to Medium
- Success Rate: 65-75%
- Time per Question: 1-2 minutes

🎯 Weightage in NEET:
- 2-3 questions per year
- 8-12 marks per year
- 4-7% of Chemistry section
- 15-20% of Physical Chemistry

Topic-wise Distribution

📚 Topic Coverage:
1. Mole Concept and Avogadro's Number: 35% of questions
2. Stoichiometry and Chemical Equations: 25% of questions
3. Concentration Terms (Molarity, Normality, etc.): 20% of questions
4. Empirical and Molecular Formula: 12% of questions
5. Limiting Reagent and Percent Yield: 8% of questions

🔍 Core Concepts and Formulas

1. Mole Concept

📝 Fundamental Definitions:
- 1 mole = 6.022 × 10²³ particles
- Number of moles = Mass/Molar mass = Volume/22.4 L = Particles/NA
- Molar mass = Mass of 1 mole of substance

🔢 Key Calculations:
- Number of atoms/molecules = n × NA
- Mass of given atoms/molecules = (n × NA)/NA × Molar mass
- Volume at STP = n × 22.4 L

2. Stoichiometry

⚖️ Stoichiometric Calculations:
- Balancing chemical equations
- Mole ratio from balanced equations
- Mass-mass relationships
- Volume-volume relationships

📊 Working Steps:
1. Write balanced chemical equation
2. Convert given quantity to moles
3. Use mole ratio to find required moles
4. Convert to desired quantity

3. Concentration Terms

🧪 Concentration Formulas:
- Molarity (M) = Moles of solute/Liters of solution
- Normality (N) = Equivalents of solute/Liters of solution
- Molality (m) = Moles of solute/Kilograms of solvent
- Mass percent = (Mass of solute/Mass of solution) × 100
- Volume percent = (Volume of solute/Volume of solution) × 100
- Parts per million (ppm) = (Mass of solute/Mass of solution) × 10⁶

🔄 Interconversions:
- Molarity to Normality: N = M × n (n = valence factor)
- Molarity to Molality: m = M/(ρ - M × M_solute)

4. Empirical and Molecular Formula

🧮 Formula Determination:
- Empirical Formula: Simplest whole number ratio
- Molecular Formula: Actual number of atoms

📊 Calculation Steps:
1. Find percentage composition
2. Convert percentages to moles
3. Divide by smallest number of moles
4. Round to nearest whole number
5. Find empirical formula
6. Calculate molecular formula using molecular mass

📈 Year-wise Question Analysis

Recent NEET Questions (2019-2024)

2024 NEET Questions

📝 Question 1: Mole Concept Calculation
A sample of glucose (C₆H₁₂O₆) contains 3.011 × 10²³ molecules. What is the mass of this sample?

Solution:
Number of molecules = 3.011 × 10²³
Avogadro's number = 6.022 × 10²³
Number of moles = 3.011 × 10²³/6.022 × 10²³ = 0.5 moles
Molar mass of glucose = 6×12 + 12×1 + 6×16 = 180 g/mol
Mass = 0.5 × 180 = 90 g

Answer: 90 g

📝 Question 2: Limiting Reagent
When 50 g of CaCO₃ reacts with 20 g of HCl, what mass of CO₂ is produced?
CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

Solution:
Moles of CaCO₃ = 50/100 = 0.5 moles
Moles of HCl = 20/36.5 = 0.55 moles
From equation: 1 mole CaCO₃ requires 2 moles HCl
For 0.5 moles CaCO₃, HCl required = 1.0 moles
HCl is limiting reagent
CO₂ produced = 0.55/2 = 0.275 moles
Mass of CO₂ = 0.275 × 44 = 12.1 g

Answer: 12.1 g

2023 NEET Questions

📝 Question 1: Molarity Calculation
What is the molarity of a solution containing 5.85 g of NaCl in 500 mL of solution?

Solution:
Mass of NaCl = 5.85 g
Molar mass of NaCl = 23 + 35.5 = 58.5 g/mol
Moles of NaCl = 5.85/58.5 = 0.1 moles
Volume of solution = 500 mL = 0.5 L
Molarity = 0.1/0.5 = 0.2 M

Answer: 0.2 M

📝 Question 2: Empirical Formula
An organic compound contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. Its molecular mass is 180. Find its molecular formula.

Solution:
Assume 100 g compound:
C = 40 g, H = 6.7 g, O = 53.3 g
Moles of C = 40/12 = 3.33
Moles of H = 6.7/1 = 6.7
Moles of O = 53.3/16 = 3.33
Mole ratio = 3.33:6.7:3.33 = 1:2:1
Empirical formula = CH₂O
Molar mass of CH₂O = 12 + 2 + 16 = 30
Molecular mass = 180
n = 180/30 = 6
Molecular formula = C₆H₁₂O₆

Answer: C₆H₁₂O₆ (Glucose)

2022 NEET Questions

📝 Question 1: Normality Calculation
What is the normality of 0.5 M H₂SO₄ solution?

Solution:
Molarity = 0.5 M
H₂SO₄ dissociates: H₂SO₄ → 2H⁺ + SO₄²⁻
Valence factor (n) = 2
Normality = Molarity × n = 0.5 × 2 = 1 N

Answer: 1 N

📝 Question 2: Volume Calculation at STP
What volume is occupied by 2.5 moles of an ideal gas at STP?

Solution:
At STP, 1 mole = 22.4 L
2.5 moles = 2.5 × 22.4 = 56 L

Answer: 56 L

🎯 Common Question Patterns

Pattern 1: Mole Concept Numericals

📊 Typical Structure:
- Given: Mass or number of particles
- Required: Number of moles, mass, or particles
- Formula: n = m/M or N = n × NA

🔢 Example Types:
1. Mass to moles conversion
2. Moles to mass conversion
3. Particles to moles conversion
4. Moles to particles conversion
5. Volume at STP calculations

Pattern 2: Stoichiometry Problems

📊 Typical Structure:
- Given: Mass/volume of reactant
- Required: Mass/volume of product
- Method: Mole ratio from balanced equation

🔢 Example Types:
1. Mass-mass calculations
2. Volume-volume calculations
3. Mass-volume calculations
4. Limiting reagent problems
5. Percent yield calculations

Pattern 3: Concentration Calculations

📊 Typical Structure:
- Given: Mass and volume
- Required: Concentration terms
- Formula: M = n/V, N = n/V × valence

🔢 Example Types:
1. Molarity calculations
2. Normality calculations
3. Molality calculations
4. Percent calculations
5. Dilution problems

Pattern 4: Formula Determination

📊 Typical Structure:
- Given: Percentage composition or analysis data
- Required: Empirical or molecular formula
- Method: Step-by-step calculation

🔢 Example Types:
1. Simple empirical formula
2. Molecular formula from empirical formula
3. Formula from combustion analysis
4. Formula from hydrate composition

⚠️ Common Mistakes and Solutions

Mistake 1: Unit Confusion

❌ Common Error:
- Using grams instead of kilograms for molality
- Using milliliters instead of liters for molarity
- Forgetting to convert units before calculations

✅ Correct Approach:
- Always check units before calculation
- Convert to SI units systematically
- Verify unit consistency in final answer

Mistake 2: Incorrect Mole Ratio

❌ Common Error:
- Using wrong coefficients from balanced equation
- Forgetting to balance the equation
- Inverting the mole ratio

✅ Correct Approach:
- Always balance the chemical equation first
- Identify correct coefficients
- Use proper mole ratio: required/available

Mistake 3: Concentration Term Confusion

❌ Common Error:
- Using molarity formula for molality
- Forgetting to account for solution density
- Confusing normality with molarity

✅ Correct Approach:
- Memorize exact definitions
- Understand differences between terms
- Practice interconversion problems

Mistake 4: Calculation Errors

❌ Common Error:
- Simple arithmetic mistakes
- Wrong placement of decimal points
- Calculator entry errors

✅ Correct Approach:
- Double-check calculations
- Verify decimal placement
- Use estimation to check reasonableness

🔧 Problem-Solving Strategies

Step-by-Step Methodology

📝 Universal Approach:
1. Read the question carefully
2. Identify what's given and what's required
3. Select appropriate formula(s)
4. Convert units if necessary
5. Perform calculations systematically
6. Check the answer for reasonableness
7. Express answer with proper units

Time-Saving Techniques

⏱️ Quick Methods:
- Learn common molecular masses by heart
- Practice mental calculations for simple problems
- Use approximation techniques for estimation
- Recognize patterns in numerical problems
- Master formula shortcuts

Verification Methods

✔️ Answer Checking:
- Unit consistency check
- Magnitude reasonableness check
- Cross-verification with alternative methods
- Boundary condition testing

📚 Practice Questions by Difficulty

Easy Level (Foundation Building)

📝 Practice Set 1:
1. Calculate the number of moles in 36 g of water.
2. Find the mass of 2.5 moles of CO₂.
3. Calculate the molarity of 4.9 g H₂SO₄ in 250 mL solution.
4. Determine the number of atoms in 2 g of sodium.
5. Find the volume occupied by 1 mole of gas at STP.

🎯 Expected Time: 1-2 minutes per question
💡 Focus: Basic formula application

Medium Level (Concept Application)

📝 Practice Set 2:
1. When 10 g of CaCO₃ is heated, what volume of CO₂ is produced at STP?
2. A solution contains 9.8 g H₂SO₄ in 500 mL. Find its normality.
3. An organic compound has empirical formula CH₂O and molecular mass 90. Find its molecular formula.
4. 20 g of NaOH reacts with excess HCl. How many moles of NaCl are formed?
5. Calculate the molality of 18 g glucose in 500 g water.

🎯 Expected Time: 2-3 minutes per question
💡 Focus: Multi-step calculations

Hard Level (Advanced Problems)

📝 Practice Set 3:
1. 5 g of an unknown hydrate loses 1.8 g on heating. Find the formula of the hydrate if the anhydrous salt has molecular mass 120.
2. A mixture of Na₂CO₃ and NaHCO₃ contains 58.5% Na₂CO₃. On heating 10 g of mixture, what mass of CO₂ is evolved?
3. Find the empirical formula of a compound containing 32.4% Na, 22.6% S, and 45.0% O.
4. 2.5 g of a metal reacts with excess oxygen to form 5.5 g of oxide. Find the atomic mass of the metal.
5. Calculate the molarity of a solution obtained by mixing 100 mL of 0.5 M HCl with 200 mL of 0.3 M HCl.

🎯 Expected Time: 3-4 minutes per question
💡 Focus: Complex multi-concept problems

📈 Performance Analysis

Success Rate by Question Type

📊 Success Rate Analysis:
- Simple mole concept: 85% success rate
- Basic stoichiometry: 75% success rate
- Concentration calculations: 70% success rate
- Formula determination: 60% success rate
- Complex problems: 45% success rate

Time Management Analysis

⏱️ Average Time Taken:
- Easy questions: 45-60 seconds
- Medium questions: 1-2 minutes
- Hard questions: 2-3 minutes
- Very hard questions: 3-4 minutes

🎯 Recommended Time Allocation:
- Total 15-18 minutes for all Physical Chemistry questions
- 2-3 minutes maximum per question
- Skip and return if taking longer than 3 minutes

Common Error Analysis

📊 Error Categories:
1. Unit errors: 25% of mistakes
2. Formula errors: 20% of mistakes
3. Calculation errors: 35% of mistakes
4. Concept errors: 15% of mistakes
5. Reading errors: 5% of mistakes

🔧 Improvement Strategies:
- Practice unit conversions regularly
- Memorize all formulas thoroughly
- Double-check all calculations
- Strengthen conceptual understanding
- Read questions carefully

🎮 Interactive Learning Features

Formula Quick Reference

📋 Essential Formulas:
1. n = m/M = N/NA = V/22.4
2. M = n/Vsolution (in L)
3. N = M × n-factor
4. m = n/ksolvent (in kg)
5. % mass = (msolute/msolution) × 100
6. Percent yield = (actual/theoretical) × 100

Common Molecular Masses

🧪 Quick Reference Table:
- H₂O: 18 g/mol
- CO₂: 44 g/mol
- NaCl: 58.5 g/mol
- H₂SO₄: 98 g/mol
- CH₄: 16 g/mol
- NH₃: 17 g/mol
- C₆H₁₂O₆: 180 g/mol

Conversion Factors

🔄 Useful Conversions:
- 1 L = 1000 mL
- 1 kg = 1000 g
- 1 mole = 6.022 × 10²³ particles
- 22.4 L = 1 mole at STP
- 1 ppm = 1 mg/L

🔄 Regular Practice Schedule

Daily Practice Routine

📅 30-Minute Daily Session:
- 10 minutes: Formula revision
- 15 minutes: Problem solving
- 5 minutes: Error analysis

📊 Weekly Progress:
- Day 1-2: Mole concept problems
- Day 3-4: Stoichiometry problems
- Day 5-6: Concentration calculations
- Day 7: Mixed practice and revision

Monthly Assessment

📈 Monthly Goals:
- Master all basic formulas
- Complete 100+ practice problems
- Achieve 80% accuracy in easy problems
- Improve speed to under 2 minutes per question
- Learn all common molecular masses

✅ Self-Assessment Checklist

Concept Mastery Checklist

☐ Mole concept and Avogadro's number
☐ Stoichiometric calculations
☐ Balancing chemical equations
☐ Concentration terms (Molarity, Normality, Molality)
☐ Percent composition calculations
☐ Empirical and molecular formula determination
☐ Limiting reagent concept
☐ Percent yield calculations
☐ Unit conversions and interconversions
☐ Density and specific gravity calculations

Problem-Solving Skills

☐ Can identify given and required quantities
☐ Can select appropriate formula
☐ Can perform unit conversions correctly
☐ Can balance chemical equations
☐ Can use mole ratios correctly
☐ Can calculate concentrations accurately
☐ Can determine empirical formulas
☐ Can solve limiting reagent problems
☐ Can complete calculations within time limit
☐ Can verify answer reasonableness

Master the fundamentals of Chemistry with this comprehensive collection of NEET PYQs! Build strong foundations, develop numerical skills, and achieve excellence in Physical Chemistry! 🧪

Every mole concept mastered strengthens your foundation for advanced Chemistry! Begin your journey to Chemistry excellence today! 🎯