Volumetric Analysis - Class12 Chemistry [pdf] - Notes & Solutions

Volumetric Analysis - Class12 Chemistry [pdf] - Notes & Solutions

Unit-1. Volumetric Analysis     :  8 teaching hrs

Introduction to gravimetric analysis, volumetric analysis and equivalent weight ; Relationship between equivalent weight, atomic weight and valency ; Equivalent weight of compounds (acid, base, salt, oxidizing and reducing agents) ; Concentration of solution and its units in terms of : Percentage, g/L , molarity, molality, normality and formality, ppm and ppb ; Primary and secondary standard substances ; Law of equivalence and normality equation ; Titration and its types: Acid-base titration, redox titration ( related numerical problems)

The unit on volumetric analysis covers several key concepts in chemistry, including gravimetric analysis, equivalent weight, and the relationships between atomic weight, valency, and equivalent weight. It also discusses the concentration of solutions in various units and the principles of titration. Here is a detailed breakdown of the topics covered:

1. Introduction to Gravimetric Analysis and Volumetric Analysis

• Gravimetric Analysis: This method involves measuring the mass of a substance produced or consumed in a chemical reaction. It is used to determine the amount of a substance present in a sample.
• Volumetric Analysis: This method involves measuring the volume of a solution required to react with a known volume of another solution. It is used to determine the concentration of a substance in a solution.

2. Equivalent Weight

• Definition: The equivalent weight of an element is the mass of that element which combines with or displaces a fixed quantity of another element. For example, the equivalent weight of magnesium is 12, meaning that 12 parts by weight of magnesium combine with or displace 1.008 parts by weight of hydrogen.
• Relationship with Atomic Weight and Valency: The equivalent weight of an element is related to its atomic weight and valency. The equivalent weight is the atomic weight divided by the valency. For example, the equivalent weight of iron in its ferrous state (Fe++) is 56/2 = 28.
• Variable Equivalent Weight: Elements with variable valency have variable equivalent weights. For example, the equivalent weight of copper in red oxide (Cu2O) is 63.5, while in black oxide (CuO) it is 31.75.

3. Equivalent Weight of Compounds

• Acid: The equivalent weight of an acid is the mass of the acid that supplies or reacts with one mole of hydrogen ions (H+). For example, the equivalent weight of hydrochloric acid (HCl) is 36.5/1 = 36.5.
• Base: The equivalent weight of a base is the mass of the base that supplies or reacts with one mole of hydrogen ions (H+). For example, the equivalent weight of sodium hydroxide (NaOH) is 40/1 = 40.
• Salt: The equivalent weight of a salt is the mass of the salt that supplies or reacts with one mole of hydrogen ions (H+). For example, the equivalent weight of sodium chloride (NaCl) is 58.5/1 = 58.5.
• Oxidizing and Reducing Agents: The equivalent weight of oxidizing and reducing agents is determined based on their chemical reactions.

4. Concentration of Solutions

• Units: Solutions can be expressed in various units, including:
  • Percentage: The percentage of a substance in a solution is calculated by dividing the mass of the substance by the mass of the solution and multiplying by 100.
  • g/L: The concentration of a solution in grams per liter is calculated by dividing the mass of the substance by the volume of the solution in liters.
  • Molarity: The molarity of a solution is the number of moles of the substance per liter of the solution.
  • Molality: The molality of a solution is the number of moles of the substance per kilogram of the solvent.
  • Normality: The normality of a solution is the number of equivalents per liter of the solution.
  • Formality: The formaldehyde of a solution is the number of formaldehyde groups per liter of the solution.
  • ppm and ppb: Parts per million (ppm) and parts per billion (ppb) are used to express very small concentrations.

5. Primary and Secondary Standard Substances

• Primary Standard Substances: Primary standard substances are used as reference points for calibration and are known to have a specific concentration. Examples include potassium hydrogen phthalate and potassium hydrogen iodate.
• Secondary Standard Substances: Secondary standard substances are used as a reference point for calibration but may not have a known concentration. Examples include oxalic acid dihydrate.

6. Law of Equivalence and Normality Equation

• Law of Equivalence: The law of equivalence states that the number of equivalents of an acid or base in a solution is equal to the number of equivalents of the other reactant.
• Normality Equation: The normality equation is used to calculate the concentration of a solution in terms of normality.

7. Titration and Its Types

• Acid-Base Titration: This type of titration involves the reaction between an acid and a base to determine the concentration of one of the reactants.
• Redox Titration: This type of titration involves the reaction between an oxidizing agent and a reducing agent to determine the concentration of one of the reactants.