Calculating Moles, Concentration, and Volume

Key Concepts

• Equation: Links number of moles of an aqueous substance to its concentration (C) and volume (V).
  • Volume is measured in decimeters cubed (dm³).
  • Concentration is measured in moles per dm³ (mol/dm³).
• Formula: ( n = C \times V )
  • n: Number of moles
  • C: Concentration
  • V: Volume

Example Problems

Problem 1: Finding Moles

• Given:
  • 800 cm³ of sodium hydroxide
  • Concentration = 0.2 mol/dm³
• Steps:
  1. Convert volume to dm³: 800 cm³ / 1000 = 0.8 dm³
  2. Calculate moles: ( 0.8 \times 0.2 = 0.16 ) moles

Problem 2: Finding Concentration

• Given:
  • Volume = 1.5 dm³
  • Moles = 0.6 moles
• Steps:
  1. Calculate concentration: ( 0.6 / 1.5 = 0.4 ) mol/dm³

Advanced Example: Reaction Calculation

Problem 3: Unknown Concentration or Volume

• Given:
  • 30 cm³ of 0.5 mol/dm³ potassium hydroxide
  • 25 cm³ of sulfuric acid
• Steps:
  1. Convert volumes to dm³:
     • Potassium hydroxide: 30 cm³ / 1000 = 0.03 dm³
     • Sulfuric acid: 25 cm³ / 1000 = 0.025 dm³
  2. Calculate moles of potassium hydroxide:
     • ( 0.5 \times 0.03 = 0.015 ) moles
  3. Find molar ratio (KOH: H₂SO₄ = 2:1)
     • Moles of H₂SO₄ = 0.015 / 2 = 0.0075 moles
  4. Calculate concentration of sulfuric acid:
     • ( 0.0075 / 0.025 = 0.3 ) mol/dm³

Conclusion

• Use the equation ( n = C \times V ) to solve for unknowns in chemistry calculations.
• Ensure all volumes are converted to dm³ for accurate calculations.
• Understand and apply molar ratios in reaction calculations.

Final Answer

• Concentration of sulfuric acid: 0.3 mol/dm³