#class 11 chemistry notes

Qualitative Analysis of Organic Compounds: Class 11 Chemistry Notes on Element and Functional Group Detection

1. Introduction

Qualitative analysis of organic compounds involves the detection of different elements (such as carbon, hydrogen, oxygen, nitrogen, sulfur, halogens, and phosphorus) present in a compound, along with identifying the functional groups (such as alcohols, aldehydes, amines, etc.).

2. Detection of Elements

The elements in organic compounds can be detected using specific tests:

2.1 Detection of Carbon and Hydrogen

Test: Heat the organic compound with copper(II) oxide (CuO). If carbon and hydrogen are present, they will oxidize to carbon dioxide (CO₂) and water (H₂O).

CO₂ Test: Pass the evolved gas through lime water (Ca(OH)₂). It turns milky due to the formation of calcium carbonate (CaCO₃).

H₂O Test: Anhydrous copper sulfate (CuSO₄), when exposed to water vapor, turns blue from its white anhydrous form.

2.2 Detection of Nitrogen

Lassaigne’s Test (Sodium Fusion Test): The organic compound is fused with sodium metal, converting nitrogen to sodium cyanide (NaCN). The cyanide ion is then detected.

Ferric chloride test: The fusion extract is boiled with ferrous sulfate (FeSO₄), followed by acidification with dilute sulfuric acid (H₂SO₄). A Prussian blue precipitate (ferric ferrocyanide) confirms the presence of nitrogen.

2.3 Detection of Sulfur

Lassaigne’s Test: When the organic compound containing sulfur is fused with sodium, sodium sulfide (Na₂S) is formed.

Lead acetate test: The sodium fusion extract is acidified with acetic acid and lead acetate solution is added. A black precipitate of lead sulfide (PbS) indicates sulfur's presence.

2.4 Detection of Halogens (Cl, Br, I)

Lassaigne’s Test: Organic compounds containing halogens, when fused with sodium, produce sodium halides (NaCl, NaBr, NaI).

  - The sodium fusion extract is acidified with nitric acid (HNO₃) and treated with silver nitrate (AgNO₃).

    - White precipitate: Chloride (Cl⁻) present.

    - Pale yellow precipitate: Bromide (Br⁻) present.

    - Yellow precipitate: Iodide (I⁻) present.

2.5 Detection of Phosphorus

- The organic compound is heated with an oxidizing agent like nitric acid (HNO₃). Phosphorus is oxidized to phosphate (PO₄³⁻).

  - Ammonium molybdate test: The solution is treated with ammonium molybdate and concentrated nitric acid. The formation of a yellow precipitate indicates the presence of phosphorus.

3. Detection of Functional Groups

3.1 Alcohols (–OH group)

Lucas Test: A mixture of zinc chloride (ZnCl₂) and concentrated hydrochloric acid (HCl) is used. Tertiary alcohols give an immediate turbidity, secondary alcohols take time, while primary alcohols do not react at room temperature.

Sodium Metal Test: Alcohols react with sodium to release hydrogen gas.

3.2 Aldehydes (–CHO group)

Fehling's Test: Aldehydes reduce Fehling’s solution (a mixture of copper(II) sulfate and sodium potassium tartrate) to red copper(I) oxide (Cu₂O).

Tollen’s Test (Silver Mirror Test): Aldehydes reduce ammoniacal silver nitrate to metallic silver, which deposits on the inside of the test tube as a silver mirror.

3.3 Carboxylic Acids (–COOH group)

- **Sodium Bicarbonate Test**: Carboxylic acids react with sodium bicarbonate (NaHCO₃) to release carbon dioxide (CO₂) gas, which can be identified by the effervescence and lime water test.

3.4 Phenols (–OH attached to benzene ring)

Ferric Chloride Test: Phenols give a violet coloration when treated with neutral ferric chloride (FeCl₃).

3.5 Amines (–NH₂ group)

Carbylamine Test: When primary amines are heated with chloroform (CHCl₃) and alcoholic potassium hydroxide (KOH), they produce an unpleasant smell of isocyanide (carbylamine).

Hinsberg’s Test: Different amines react distinctly with benzene sulfonyl chloride. Primary amines form soluble sulfonamides, secondary amines form insoluble sulfonamides, while tertiary amines do not react.

4. Solubility Tests

The solubility of organic compounds can also give clues about the nature of functional groups present:

Soluble in Water: Compounds containing –OH, –NH₂, –COOH, etc.

Soluble in Ether: Non-polar compounds such as hydrocarbons.

5. Summary of Important Tests

Class 11 Chemistry: Nomenclature of Organic Compounds:

Understanding the nomenclature of organic compounds is fundamental in chemistry. It allows for the systematic naming of organic molecules, ensuring clarity and consistency in communication. This guide covers the essential rules and examples based on the IUPAC (International Union of Pure and Applied Chemistry) system, which is widely used in academic and professional settings.

1. Introduction to Organic Nomenclature:

Organic Compounds: Compounds primarily composed of carbon (C) and hydrogen (H), often with heteroatoms like oxygen (O), nitrogen (N), sulfur (S), etc.

Nomenclature Importance: Provides a standardized method to name compounds, facilitating understanding and communication in chemistry.

2. IUPAC Nomenclature Rules:

The IUPAC system follows a set of rules to name organic compounds systematically:

1. Identify the longest carbon chain as the parent hydrocarbon.

2. Number the chain from the end nearest a substituent.

3. Identify and name the substituents (alkyl groups, halogens, etc.).

4. Assign numbers to substituents based on their positions on the main chain.

5. Combine the names using prefixes, infixes, and suffixes appropriately.

3. Naming Alkanes:

Alkanes are saturated hydrocarbons with single C–C bonds.

3.1. Straight-Chain Alkanes:

3.2. Branched-Chain Alkanes

Substituents: Alkyl groups attached to the main chain (e.g., methyl, ethyl).

Naming: Indicate substituents with their position numbers.

Example:

2-Methylpropane

  - Parent chain: Propane (3 carbons)

  - Substituent: Methyl group on the second carbon

3.3. Multiple Substituents

Use prefixes like di-, tri-, tetra- for multiple identical substituents.

List substituents in alphabetical order regardless of their position numbers.

Example:

-2,2-Dimethylbutane

-Parent chain: Butane (4 carbons)

-Two methyl groups on the second carbon

4. Naming Alkenes and Alkynes:

Alkenes and alkynes contain double and triple bonds, respectively.

4.1. Alkenes

- Suffix: `-ene`

- Number the chain to give the double bond the lowest possible number.

- Position of the double bond is indicated by a number.

Example:

- But-2-ene

  - Parent chain: Butane (4 carbons)

  - Double bond starting at the second carbon

4.2. Alkynes

- Suffix: `-yne`

- Number the chain to give the triple bond the lowest possible number.

- Position of the triple bond is indicated by a number.

Example:

- Pent-1-yne

  - Parent chain: Pentane (5 carbons)

  - Triple bond starting at the first carbon

5. Naming Haloalkanes (Halo Compounds)

Haloalkanes contain halogen substituents (F, Cl, Br, I).

5.1. General Rules

1. Identify the longest carbon chain containing the halogen.

2. Name the halogen as a substituent (fluoro-, chloro-, bromo-, iodo-).

3. Number the chain to give the halogen the lowest possible number.

Example:

- 2-Chloropropane

  - Parent chain: Propane (3 carbons)

  - Chlorine on the second carbon

5.2. Multiple Halogen Substituents

- Use prefixes like di-, tri-, tetra-.

- List substituents in alphabetical order.

Example:

- 1,2-Dibromobutane

  - Parent chain: Butane (4 carbons)

  - Bromine atoms on the first and second carbons

6. Naming Alcohols

Alcohols contain the hydroxyl group (-OH).

6.1. General Rules

1. Identify the longest carbon chain** containing the hydroxyl group.

2. Name the parent chain by replacing the `-e` of the corresponding alkane with `-ol`.

3. Number the chain to give the hydroxyl group the lowest possible number.

Example:

- Butan-2-ol

  - Parent chain: Butane (4 carbons)

  - Hydroxyl group on the second carbon

6.2. Multiple Hydroxyl Groups

Use prefixes like diol, triol, etc.

Example:

- 1,2-Ethanediol (commonly known as ethylene glycol)

7. Naming Ethers

Ethers contain an oxygen atom connecting two alkyl or aryl groups.

7.1. General Rules

1. Name the two alkyl groups attached to the oxygen.

2. Use the word "ether" or the suffix `-oxy`.

3. List the alkyl groups in alphabetical order.

Example:

- Methoxyethane

  - Methoxy group (–O–CH₃)

  - Ethane group (–CH₂CH₃)

8. Naming Aldehydes

Aldehydes contain the carbonyl group (–CHO) at the end of the carbon chain.

8.1. General Rules

1. Identify the longest carbon chain containing the carbonyl group.

2. Replace the `-e` of the corresponding alkane with `-al`.

3. Number the chain starting from the carbonyl carbon.

Example:

- Butanal

  - Parent chain: Butane (4 carbons)

  - Aldehyde group on the first carbon

9. Naming Ketones

Ketones contain the carbonyl group (C=O) within the carbon chain.

9.1. General Rules

1. Identify the longest carbon chain** containing the carbonyl group.

2. Replace the `-e` of the corresponding alkane with `-one`.

3. Number the chain to give the carbonyl group the lowest possible number.

4. Indicate the position of the carbonyl group with a number.

Example:

- Butan-2-one

  - Parent chain: Butane (4 carbons)

  - Carbonyl group on the second carbon

10. Naming Carboxylic Acids and Derivatives

Carboxylic acids contain the carboxyl group (–COOH). Derivatives include esters, amides, acid chlorides, etc.

10.1. Carboxylic Acids

General Rules:

1. Identify the longest carbon chain containing the carboxyl group.

2. Replace the `-e` of the corresponding alkane with `-oic acid`.

3. Number the chain starting from the carboxyl carbon (always carbon 1).

Example:

- Ethanoic acid (commonly known as acetic acid)

  - Parent chain: Ethane (2 carbons)

  - Carboxyl group on the first carbon

10.2. Esters

Esters are derivatives of carboxylic acids where the –OH is replaced by an –OR group.

Naming Rules:

1. Name the alkyl group attached to the oxygen first.

2. Name the parent carboxylic acid with the suffix `-oate`.

Example:

- Methyl ethanoate

  - Methyl group attached to oxygen

  - Ethanoate from ethanoic acid

10.3. Acid Chlorides

Acid chlorides are derivatives where the –OH of the carboxyl group is replaced by a chlorine atom.

Naming Rules:

- Replace the `-ic acid` suffix with `-oyl chloride`.

Example:

-Ethanoic acid → Ethanooyl chloride

11. Naming Amines

Amines contain nitrogen atoms attached to alkyl or aryl groups.

11.1. General Rules

1. Identify the longest carbon chain attached to the nitrogen.

2. Name the substituents attached to the nitrogen.

3. Use the suffix `-amine`.

Example:

- N-Methylmethanamine

  - Methyl group attached to nitrogen

  - Methanamine as the parent amine

11.2. Multiple Amino Groups

Use prefixes like di-, tri-, etc.

Example:

- N,N-Dimethylpropylamine

  - Two methyl groups attached to nitrogen

  - Propyl group as the parent amine

12. Common Names vs. IUPAC Names

While IUPAC names are systematic and widely accepted, many organic compounds also have common names, often derived from historical or trivial sources.

Examples:

-Common Name: Acetone | IUPAC Name: Propan-2-one

-Common Name: Ethyl alcohol | IUPAC Name: Ethanol

- Common Name: Methyl chloride | IUPAC Name: Chloromethane

Note: In scientific communication, IUPAC names are preferred for clarity.

13. Practice Problems

Problem 1:

Name the following compound:

But-2-ene with a methyl group on carbon 3

Solution:

- Parent chain: But-2-ene

- Substituent: Methyl group on carbon 3

- Name: 3-Methylbut-2-ene

Problem 2:

Name the compound with the formula CH₃CH₂CH₂OH.

Solution:

- Parent chain: Propanol (3 carbons)

- Hydroxyl group on carbon 1

- Name: 1-Propanol

Problem 3:

Name the following compound:

CH₃CHClCH₂CH₃

Solution:

- Parent chain: Butane

- Chlorine on carbon 2

- Name: 2-Chlorobutane

14. Summary

Bohrs Model of Hydrogen Atom - Class 11 Chemistry Notes

Introduction

Bohr's model of the hydrogen atom, proposed by Niels Bohr in 1913, was a significant advancement in atomic theory. This model provided a quantum explanation for the hydrogen atom's structure, overcoming the limitations of Rutherford's atomic model, which could not explain the stability of atoms. Bohr's model successfully explained the spectral lines of hydrogen and laid the groundwork for modern quantum mechanics.

Key Postulates of Bohr's Model

1. Quantized Orbits:

   - Electrons revolve around the nucleus in fixed, quantized orbits or energy levels, which are designated by quantum numbers (n = 1, 2, 3,...).

   - The energy of an electron in a particular orbit is constant and does not change as long as it remains in that orbit.

2. Angular Momentum Quantization:

   - The angular momentum of an electron in a given orbit is quantised and is an integral multiple of h/2π​, where ( h) is Planck’s constant.

Mathematically, it is expressed as:

     mvr = nh ​/ 2π

     where ( m ) is the mass of the electron, ( v ) is its velocity, ( r ) is the radius of the orbit, and ( n ) is the principal quantum number.

3. Energy Levels and Emission of Photons:

   - When an electron jumps from a higher energy level (excited state) to a lower energy level (ground state), it emits energy in the form of a photon.

   - The energy difference between the two levels corresponds to the energy of the emitted photon:

ΔE = E2​−E1​= hν

     where ν is the frequency of the emitted radiation.

4. Stationary Orbits:

   - Electrons in stationary orbits do not radiate energy. This postulate resolved the classical paradox where accelerating charged particles were expected to emit electromagnetic radiation, leading to the collapse of the atom.

Read Also: Genesis of Periodic Classification Class 11 Notes

Bohr's Radius and Energy of Orbits

1. Bohr's Radius:

The radius of the nth orbit of the hydrogen atom is given by:

     rn​: n2h2ϵ0​/ πme2

​

 For the first orbit ( n = 1), this reduces to a value known as Bohr’s radius ( r_1 ≈0.529A˚

2. Energy of an Electron:

   - The energy of an electron in the  n^{th} orbit of a hydrogen atom is given by:

     En​ = - 13.6eV​ /n2

This equation shows that energy is negative, indicating that the electron is bound to the nucleus.

Explanation of the Hydrogen Spectrum

Bohr's model explains the hydrogen emission spectrum, which consists of several spectral series:

Lyman Series: Transitions from higher energy levels to n = 1.

Balmer Series: Transitions from higher energy levels to n = 2.

Paschen Series: Transitions from higher energy levels to n = 3.

Each series corresponds to photons of different wavelengths, and these series are observed in different regions of the electromagnetic spectrum.

Limitations of Bohr's Model

While Bohr’s model was revolutionary, it had several limitations:

1. Multi-Electron Atoms:

Bohr’s model is primarily applicable to hydrogen and hydrogen-like (single-electron) atoms. It fails to accurately predict the spectra of multi-electron atoms.

2. Zeeman and Stark Effects:

The model does not explain the splitting of spectral lines in the presence of magnetic (Zeeman effect) or electric fields (Stark effect).

3. Wave-Particle Duality:

Bohr’s model does not account for the wave nature of electrons, as later described by de Broglie’s hypothesis and Schrödinger's wave equation.

4. No Explanation for the Fine Structure:

The fine structure of spectral lines, observed at higher resolutions, is not explained by Bohr’s model.

Conclusion