Some Basic Concepts of Chemistry for NEET
This chapter is the numerical foundation of NEET Chemistry. Most questions become manageable when you convert the information into moles first and use a balanced chemical equation as a mole-ratio map.
Instead of memorising separate shortcuts for every question, practise a stable sequence: identify what is given, convert it to moles, apply the required chemical ratio and convert to the final unit asked in the question.
Topics to revise before practice
Mole concept
Relate mass, molar mass, particles and amount of substance.
Stoichiometry
Use balanced-equation coefficients as mole ratios.
Limiting reagent
Find which reactant is consumed first and limits the product.
Empirical formula
Convert percentage composition into the simplest whole-number ratio.
Concentration terms
Apply molarity, molality, mole fraction and mass percentage correctly.
Significant figures
Report numerical answers with suitable precision.
Formula and concept recall
A reliable approach for Chemistry numericals
Write the given data with units
Separate mass, volume, concentration and particle count. This prevents using a formula with the wrong quantity.
Convert to moles
For mass use n = mass/molar mass. For particles use Avogadro constant. For a solution use molarity and volume when appropriate.
Use the balanced equation
Coefficients represent mole ratios. In a limiting-reagent question, calculate the product possible from each reactant.
Convert to the requested answer
Only after the mole-ratio step convert to grams, litres, molecules, percentage composition or another requested unit.
Some Basic Concepts of Chemistry Questions with Solutions
Attempt each question without opening the solution. Then compare your method, not only the final option.
How many moles are present in 18 g of water (H2O)?
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Answer: B. Molar mass of H2O = 2(1) + 16 = 18 g mol-1. Therefore, moles = 18/18 = 1 mol.
The number of molecules in 0.5 mol of O2 is:
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Answer: B. Number of molecules = 0.5 × 6.022 × 1023 = 3.011 × 1023.
For the reaction 2H2 + O2 → 2H2O, how many moles of water are formed from 3 mol of H2 when O2 is in excess?
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Answer: C. The balanced equation gives a 2:2 mole ratio between H2 and H2O. Thus, 3 mol H2 produces 3 mol H2O.
What is the molarity of a solution containing 0.5 mol NaOH in 250 mL of solution?
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Answer: C. Volume = 250 mL = 0.250 L. Molarity = 0.5/0.250 = 2 M.
For N2 + 3H2 → 2NH3, a mixture contains 1 mol N2 and 2 mol H2. The limiting reagent is:
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Answer: B. 1 mol N2 requires 3 mol H2, but only 2 mol H2 is available. Therefore H2 is limiting.
A compound contains 40% carbon, 6.67% hydrogen and 53.33% oxygen by mass. Its empirical formula is:
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Answer: B. Assume 100 g: C = 40/12 = 3.33 mol, H = 6.67/1 = 6.67 mol, O = 53.33/16 = 3.33 mol. Divide by 3.33 to get 1:2:1, hence CH2O.
A solution has 2 mol ethanol and 8 mol water. The mole fraction of ethanol is:
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Answer: B. Total moles = 2 + 8 = 10. Mole fraction of ethanol = 2/10 = 0.20.
The percentage by mass of oxygen in H2SO4 (H = 1, S = 32, O = 16) is approximately:
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Answer: C. Molar mass of H2SO4 = 2 + 32 + 64 = 98. Oxygen mass = 64. Percentage oxygen = (64/98) × 100 ≈ 65.31%.
Continue your NEET Chemistry practice
After these solved examples, take a timed test. Review each wrong or guessed question and write the exact conversion or mole-ratio step that caused the error.
Try the Free Chapter TestCommon errors to avoid
- Using mass ratios directly without first converting substances to moles.
- Forgetting to balance the chemical equation before using coefficients.
- Using solution volume in mL instead of litre for molarity.
- Confusing molarity with molality.
- Choosing a limiting reagent before comparing the stoichiometric requirement.
- Rounding empirical-formula ratios too early.
- Counting atoms when the question asks for molecules or formula units.
Some Basic Concepts of Chemistry FAQs
Which topics are most important for NEET in this chapter?
Focus on mole concept, molar mass, Avogadro constant, stoichiometry, limiting reagent, percentage composition, empirical and molecular formulae, concentration terms and significant figures.
What is the safest first step in a stoichiometry question?
Balance the equation and convert the supplied quantity into moles. The equation coefficients can then be used as a mole ratio.
How do I identify a limiting reagent?
Convert every reactant amount to moles and compare moles divided by the corresponding balanced-equation coefficient. The smaller value identifies the limiting reactant.
Are these official NEET previous-year questions?
No. These are original NEET-style practice questions written for revision and are not represented as official NEET previous-year questions.