Mole Concepts Lecture Notes

Introduction

• Focus on formulas, tips, and tricks for solving numerical problems related to mole concepts.

Key Terms Defined

Atomic Mass

• Definition: Mass of one atom (expressed in atomic mass units, u).

Molecular Mass

• Definition: Mass of a single molecule (also expressed in u).

Molar Mass

• Definition: Mass of one mole (6.022 x 10^23 particles).
• Distinction:
  • Atomic/Molecular Mass: Mass of 1 particle.
  • Molar Mass: Mass of 6.022 x 10^23 particles.

Categories of Molar Mass

1. Gram Atomic Mass (GAM): Mass of 6.022 x 10^23 atoms.
2. Gram Molecular Mass (GMM): Mass of 6.022 x 10^23 molecules.

Example: Nitrogen

• Atomic Mass: 14u (mass of one atom).
• Gram Atomic Mass: 14 grams (mass of one mole of atoms).

Important Atomic Masses to Remember

• Only need to remember ~28-30 key atomic masses out of 118 elements.

Molecular Mass Calculation Examples

1. Water (H2O):
   • 2(H) + 1(O) = 2(1) + 16 = 18u.
2. Calcium Hydroxide (Ca(OH)2):
   • Ca = 40 + 2(16 + 1) = 40 + 34 = 74u.
3. Sodium Sulfate Decahydrate (Na2SO4.10H2O):
   • 2(Na) + 1(S) + 4(O) + 10(H2O) = 2(23) + 32 + 4(16) + 10(18).
   • Calculation: Use values to find total molecular mass.

Relationship Between Mole, Molar Mass, and Molar Volume

• 1 mole = 6.022 x 10^23 particles.
• Molar Volume: At STP, 1 mole of gas = 22.4 L.
  • STP: 1 atm pressure, 273 K temperature.

Important Formulas

1. For Atomic Substance:

   • Number of moles (n) = Given mass (m) / Gram Atomic Mass (GAM)
   • Shortened: n = m / GAM

2. For Molecular Substance:

   • Number of moles (n) = Given mass (m) / Gram Molecular Mass (GMM)
   • Shortened: n = m / GMM

3. For Gaseous Substance:

   • Number of moles (n) = Volume at STP (in L) / 22.4 L
   • Shortened: n = V / 22.4 L

4. For Particles:

   • Number of moles (n) = Number of particles (N) / Avogadro's number (Na)
   • Shortened: n = N / Na

Sample Exercises

1. Calculate number of moles in 392g of H2SO4:

   • Find GMM: 2(1) + 32 + 4(16) = 98 g.
   • Use n = m / GMM to find moles.

2. Calculate number of moles in 44.8 L of CO2 at STP:

   • Use n = V / 22.4 L.

3. Find number of atoms in 53g of Na2CO3:

   • Calculate number of moles, then use it to find number of molecules and atoms by stoichiometry.

4. Calculate moles from 350 cm³ CO2 at 273K and 2 atm:

   • Convert conditions to STP using the ideal gas law, then find moles.

5. Calculate mass of one atom of silver:

   • Use the unitary method: Mass of one atom = (GAM) / (6.022 x 10^23).

Conclusion

• Understanding these formulas and how to apply them is crucial for solving mole concept numerical problems.
• Encourage interaction for questions and doubts.