Mole Concept & Molar Masses
1. Why We Need Moles
Atoms and molecules are super tiny! 🧪 Even a small amount of any substance contains a huge number of particles. To count them easily, we use the mole (just like “dozen” for 12 items).
2. What is a Mole?
1 mole (mol) = \(6.022 \times 10^{23}\) elementary entities. This is called Avogadro’s number (\(N_A\)).
Examples:
- 1 mol hydrogen atoms = \(6.022 \times 10^{23}\) atoms
- 1 mol water molecules = \(6.022 \times 10^{23}\) water molecules 💧
- 1 mol NaCl = \(6.022 \times 10^{23}\) NaCl formula units
Fun fact: \(6.022 \times 10^{23}\) looks like this: 602,213,670,000,000,000,000,000!
3. Molar Mass
The mass of 1 mole of a substance (in grams) is its molar mass. 🔍
Key rule: Molar mass (g/mol) = Atomic/Molecular mass in “u”.
Examples:
- Water (H₂O) molecular mass = 18.02 u → Molar mass = 18.02 g/mol
- Sodium chloride (NaCl) formula mass = 58.5 u → Molar mass = 58.5 g/mol
4. Calculating Molecular Mass (Example)
Glucose (C₆H₁₂O₆):
- Atomic mass C = 12.011 u, H = 1.008 u, O = 16.00 u
- Molecular mass = \(6 \times 12.011 + 12 \times 1.008 + 6 \times 16.00\)
- = \(72.066 + 12.096 + 96.00\) = 180.162 u
→ Molar mass of glucose = 180.162 g/mol
5. Percentage Composition
This helps find the % of each element in a compound. 🧮 (Example calculation not shown in text, but super useful for exams!)
NEET Spotlight 🔥 (High-Yield Concepts)
- Avogadro’s number: Always \(6.022 \times 10^{23}\) particles/mol.
- Molar mass = Atomic/molecular mass in grams (e.g., NaCl molar mass = 58.5 g/mol).
- Molecular mass calculations (like glucose C₆H₁₂O₆ = 180 u).
- Mole conversions: Use \(N = n \times N_A\) (N = particles, n = moles).
- Formula mass vs. molecular mass (e.g., NaCl is formula mass; glucose is molecular mass).
