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Resonance in Chemistry, Equivalent Concept & Titration

For Class 11/12, Entrance Exams (NEET, JEE), and University Basics

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1. Resonance in Chemistry

Definition:

Resonance is the delocalization of electrons in a molecule where a single Lewis structure cannot accurately represent the molecule.

In simple terms:
Resonance occurs when more than one structure can be drawn for a molecule by only changing the position of electrons, not atoms.

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Key Points:

• The actual structure is a resonance hybrid, not any one of the individual forms.

• Resonance increases the stability of the molecule.

• Shown by double-headed arrows (↔).

Example: Benzene (C₆H₆):

The real structure is a hybrid with equal bond lengths between carbon atoms.

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2. Equivalent Concept in Chemistry

Definition:

An equivalent is the amount of a substance that will react with or supply one mole of H⁺ ions (acid-base) or one mole of electrons (redox).

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Formula:

Equivalent weight (E) =

Molar Mass (M)n-factor\frac{\text{Molar Mass (M)}}{\text{n-factor}}n-factorMolar Mass (M)​

Where:

• n-factor = number of H⁺ ions replaced (acid-base)
       = number of electrons transferred (redox)

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Examples:

• H₂SO₄ (Sulfuric acid):
  Molar mass = 98 g/mol, n-factor = 2
  ⇒ Equivalent weight = 98 / 2 = 49 g/eq

• NaOH:
  Molar mass = 40, n-factor = 1
  ⇒ Equivalent weight = 40 g/eq

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3. Titration (Acid-Base Reaction Method)

Definition:

Titration is a quantitative chemical analysis used to determine the concentration of an unknown solution using a solution of known concentration.

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Types:

1. Acid–Base Titration

2. Redox Titration

3. Complexometric Titration

4. Precipitation Titration

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Basic Acid–Base Titration Equation:

N1V1=N2V2N_1V_1 = N_2V_2N1​V1​=N2​V2​

Where:

• N₁ = Normality of acid

• V₁ = Volume of acid

• N₂ = Normality of base

• V₂ = Volume of base

Used to find unknown normality or volume.

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Indicators Used:

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In Summary:

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Resonance Chemistry Equivalent Concept & Titration

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