Organic Chemistry Some Basic Principles and Techniques NEET Questions 2025

A student needs to remember the basics of Organic Chemistry. Some of the basic points that a student should remember are as follows:

• All organic compounds are made up of carbon and hydrogen only.

• The character of the hybridised orbital of compounds is very important and determines characteristics like bond length, bond energy or bond strength, bond angle, and structure of compounds.

• Isomerism is the phenomenon wherein two or more compounds have different properties but the same molecular formula.

• There are two main types of isomerism, that is, structural isomerism and stereoisomerism.

• Structural isomerism is exhibited by compounds that have a different structure but the same molecular formula. They are further divided into chain isomerism, position isomerism, functional group isomerism, and metamerism.

• Stereoisomerism is exhibited by compounds that have different arrangements of atoms or groups of atoms in space but the same molecular formula. Stereoisomers are also of two types, that is, geometrical isomers and optical isomers.

• There are three types of reaction intermediates formed: free radical, carbocation, and carbanion.

• Free radicals are those atoms or groups of atoms that have an unpaired electron.

• A carbocation is a group of atoms that have only six electrons and contain a positive charge.

• Carbanions are groups of atoms that contain negatively charged carbon atoms.

• An electrophile is electron-deficient and therefore can accept a pair of electrons. These are thus positively charged or neutral species.

• Neutrophiles are electron-rich species and, therefore, donate their electrons to other species.

• Functional groups are atoms or groups of atoms that determine the characteristic property of organic compounds. These functional groups form the basis of IUPAC nomenclature. The IUPAC rules essential for attempting NEET 2025 Organic Chemistry paper are tabulated below:

Topics of Some Basic Principles and Techniques of Chemistry

1. General Introduction: Chemistry, the study of matter and its properties, plays a vital role in our lives. It helps us comprehend the world at its smallest scale and has far-reaching applications in fields like medicine, engineering, and environmental science. From life-saving drugs to innovative materials, chemistry fuels progress and innovation. It is the science that underpins our everyday existence, and its exploration reveals the universe's fundamental secrets.

2. Laws of chemical combination: The laws of chemical combination are fundamental principles that govern how substances react and combine to form new compounds. These laws include:

1. Law of Conservation of Mass: This law states that the total mass of substances before a chemical reaction is equal to the total mass after the reaction. In simple terms, matter is neither created nor destroyed in a chemical reaction.

2. Law of Definite Proportions: This law asserts that a pure compound always contains the same elements in the same fixed proportions by mass. Regardless of the source or preparation method, a compound's composition remains consistent.

3. Law of Multiple Proportions: When two elements form multiple compounds, the ratio of masses of one element that combines with a fixed mass of the other can be expressed in small whole numbers.

These laws are the building blocks of chemical reactions and have a profound impact on how we understand and predict the behavior of matter in chemistry.

3. Dalton's theory: Concept of elements, atoms and molecules: Dalton's Atomic Theory, proposed by the scientist John Dalton, is a foundational concept in chemistry. It comprises three main ideas:

Elements: Dalton suggested that all matter is composed of tiny, indivisible particles called atoms. These atoms are unique to each element and are the basic building blocks of matter.

Atoms: According to Dalton, atoms of the same element are identical in size, mass, and properties, while atoms of different elements have distinct characteristics. Atoms cannot be created, divided, or destroyed in chemical reactions.

Molecules: Dalton introduced the concept of molecules, which are formed when atoms of different elements combine in fixed ratios to create compounds. These molecules have specific structures and properties based on the arrangement of their constituent atoms.

Dalton's Atomic Theory laid the groundwork for understanding the composition of matter and the behavior of substances in chemical reactions, making it a fundamental concept in chemistry.

4. Atomic and molecular masses: Atomic and molecular masses are crucial concepts in chemistry. The atomic mass of an element is the average mass of its atoms, measured in atomic mass units (u). It's calculated by considering the naturally occurring isotopes and their relative abundances.

Molecular mass, on the other hand, refers to the sum of the atomic masses of all the atoms in a molecule. This value is expressed in atomic mass units as well.

Both atomic and molecular masses play a vital role in stoichiometry, helping chemists determine the amounts of substances involved in chemical reactions. These concepts allow scientists to understand and predict the behavior of matter, making them fundamental in the study of chemistry.

5. Mole concept and molar mass; percentage composition and empirical and molar formula; chemical reactions: The mole concept is fundamental to chemistry and involves counting entities in moles, with one mole equaling $6.022 \times 10^23$ particles (Avogadro's number). Molar mass represents the mass of one mole of a substance, measured in g/mol, calculated by summing atomic masses. Percentage composition reveals the element proportions in a compound by mass. Empirical formulas express the simplest whole-number element ratio, and molecular formulas provide the exact element counts. These concepts are crucial for chemical reactions, helping predict and control reactant and product quantities in various applications.

6. Stoichiometry and calculations based on stoichiometry: Stoichiometry is the foundation of quantitative chemistry, dealing with the precise measurement of reactants and products in chemical reactions. It relies on balanced chemical equations to establish mole ratios and enables the conversion of moles of different substances using molar masses. These calculations are indispensable for tasks like determining the right amount of reactants for a reaction, estimating product yields, or assessing the environmental consequences of chemical processes.

Important formulas from Some Basic Principles and Techniques of Chemistry

1. Number of molecules in W grams of a substance:

$\dfrac{W}{\text{Molecular mass}} \times NA$

2. Molality:

$\dfrac{\text{Number of moles of solute}}{{Mass of solvent (kg)}}$

3. Number of molecules in V liters of gas at STP:

$\dfrac{V}{22.4 L} \times NA$

4. Number of gram atoms:

$\dfrac{W}{\text{Gram atomic mass}}$

5. Number of gram molecules:

$\dfrac{W}{\text{Gram molecular mass}}$

6. Dilution formula for mixing two solutions of the same substance:

$M_1V_1 = M_2V_2$

$M_1V_1 + M_2V_2 = M_3(V_1 + V_2)$

7. Molarity can be directly calculated from % by mass if density (d) is known:

Molarity $= % \times 10 \times \dfrac{d}{GMM}$

8. Mass of 1 atom of an element:

GAM(gramatomicmass) / NA

9. Mass of 1 molecule of a substance:

GMM(grammolecularmass) / NA

10. Temperature in Kelvin can be converted to degree Celsius as follows:

T(K) = T(°C) + 273.15

11. Relative atomic mass:

$\dfrac{\text{Mass of an atom of the element}}{\dfrac{1}{12} \times \text{Mass of a carbon atom (C-12)}}$

12. Number of molecules in n moles of a substance:

n × NA

13. Mass % of an element in a compound:

(Mass of element / Molecular mass of compound) × 100

14. Mass percent:

(Mass of solute / Mass of solution) × 100

15. Boiling point formula:

XB−XB=Molality×MA1000

where MA = Mass of solvent (g)

16. Molarity (M):

$\dfrac{\text{Number of moles of solute}}{\text{Volume of solution (L)}}$

17. Avogadro's Number (NA):

$6.022 \times 10^{23}$

18. Fahrenheit to Celsius conversion formula:

T(°F) = $\dfrac{9}{5} \times$ T(°C) + 32

19. Molecular mass:

2 × Vapour density

20. Mole fraction of A:

$\dfrac{\text{Number of moles of A}}{\text{Number of moles of A + Number of moles of solution}}$

NEET 2025: Chemistry Important Chapters

NEET 2025 Preparation Tips

• Understand the NEET pattern, marking scheme, weightage.

• Study the NCERT syllabus in depth and carefully select the reference materials.

• Stick to a strict schedule for studying and stay away from distractions.

• Take down notes.

• Have sessions of regular revision.

• Solve Sample question papers.

• Keep up a healthy lifestyle.

Conclusion

The level of competition for the NEET Exam is rising year after year.  One needs to have the finest strategy if they want to succeed and be qualified to get a medical seat. A study plan, complete revisions, knowledge of the NCERT curriculum for classes 11 and 12, and familiarity with previous question papers must all be included in the strategy. Aspirants must consider these important questions provided by Vedantu as part of their revision for the NEET 2025 Exam.

NEET Chemistry Important Questions - Chapter Pages