Class 11 Chemistry: Basic Concepts of Chemistry

Reactions in Solutions

• All reactions in the lab are conducted in solution form.
• Solids must be dissolved in a liquid to react.

Understanding Solutions

• A solution consists of two components:
  • Solute: Present in smaller amounts.
  • Solvent: Present in larger amounts.
• Example: NaCl solution
  • Solute: NaCl (small amount)
  • Solvent: Water (large amount)

Concentration Terms

• Describes the amount of solute in a given amount of solvent.
• Includes:
  1. Mass by Mass Percentage (Mass %) :
     • Mass of solute per 100 grams of solution.
     • Formula: ( \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100 )
     • Example: 5% NaCl means 5g of NaCl in 100g of solution.
  2. Mole Fraction:
     • Ratio of moles of a component to total moles in the solution.
     • ( x_A = \frac{\text{Number of moles of A}}{\text{Total moles of all components}} )
     • Example problem: Calculate mole fraction of sugar in a solution.
     • Sum of mole fractions of a solution's components is always 1.
  3. Molarity (M):
     • Moles of solute per liter of solution.
     • Formula: ( M = \frac{n}{V} ) where ( n ) is number of moles and ( V ) is volume in liters.
     • Units: moles/L
     • Example problem provided.
     • Molarity is temperature dependent.
  4. Molality (m):
     • Moles of solute per kg of solvent.
     • Formula: ( m = \frac{\text{mass of solute}}{\text{molar mass of solute}} \times \frac{1}{\text{mass of solvent in kg}} )
     • Units: moles/kg
     • Temperature independent, more preferred than molarity.

Notes on Concentration Changes

• Molarity varies with temperature due to volume changes.
• Molality does not change with temperature, hence more stable.

Application in Industries

• Mass % is used in medicine labeling (e.g., syrup and tablet ingredients).
• Mole Fraction and other concentration terms are crucial for accurately preparing solutions.

Conclusion

• Understanding these concentration terms is crucial for predicting reaction outcomes and solution properties.
• Further competitive exam-related content to be covered in future sessions.
• Feedback requested from students on future topics.