Grade 10 SCIENCE Law of Conservation of Mass

Introduction to the Law of Conservation of Mass

  • The law states that matter cannot be created or destroyed in a chemical reaction.

  • Total mass of reactants = Total mass of products.

  • Essential for balancing chemical equations.

Balancing Chemical Equations

  • Counting atoms in reactants vs. products to ensure equality.

  • If any one element's count is unequal, the equation is not balanced.

  • Examples of elements used include: carbon, hydrogen, oxygen.

Importance of Atomic Mass

  • Atomic mass indicates the mass of an atom, generally presented with decimal values.

  • For simplification, use rounded atomic masses for calculations.

  • Common atomic masses include:

    • Hydrogen (H): 1

    • Helium (He): 4

    • Lithium (Li): 7

    • Beryllium (Be): 9

    • Boron (B): 11

    • Carbon (C): 12

    • Nitrogen (N): 14

    • Oxygen (O): 16

    • Fluorine (F): 19

    • Neon (Ne): 20

Calculating Masses in Chemical Reactions

Example 1: Aluminum and Oxygen Reaction

  • Balanced equation provided in a previous video.

  • Aluminum (Al): 27 g

  • Oxygen (O): 16 g

  • Calculating reactants:

    • 4 Al: 4 x 27 = 108 g

    • 3 O: 3 x 16 = 48 g

    • Total mass of reactants = 108 + 48 = 204 g

  • Calculating products:

    • 2 Al2O3: 2 x 27 x 2 = 108 g

    • 3 O2: 2 x 16 x 3 = 96 g

    • Total mass of products = 108 + 96 = 204 g

  • Conclusion: Mass is conserved (204 g).

Example 2: Sodium and Chlorine Reaction

  • Sodium (Na): 23 g

  • Chlorine (Cl): 35.5 g

  • Calculating reactants:

    • 2 Na: 2 x 23 = 46 g

    • 2 Cl: 2 x 35.5 = 71 g

    • Total mass = 46 + 71 = 117 g

  • Conclusion: Mass is conserved (117 g).

Example 3: Iron Oxides and Carbon Reaction

  • Iron (Fe): 56 g

  • Carbon (C): 12 g

  • Oxygen (O): 16 g

  • Calculating reactants:

    • 2 Fe2O3: 56 x 2 = 112 g

    • 3 C: 3 x 12 = 36 g

    • Total mass = 112 + 48 + 36 = 196 g

  • Calculating products:

    • 4 Fe: 4 x 56 = 224 g

    • 3 CO2: 3 x 12 = 36g

    • 2 O2: 16 x 2 = 32 g

    • Total mass = 224 + 36 + 32 = 292 g

  • Conclusion: Check if mass is conserved.

Conclusion

  • Mastery of atomic masses and the law of conservation of mass is crucial for balancing equations and understanding chemical reactions.

  • Students are encouraged to apply these calculations in their learning activity sheets.

  • Open for questions in the comments!