APNA CAREER

Advertisement

📘 Complete Solution

📌 Given Data

Mass of H₂O = 18 g

Atomic mass of H = 1
Atomic mass of O = 16

N_A = 6.022 × 10²³ mol⁻¹

🔵 Step 1: Calculate Molar Mass of H₂O

Molar Mass of H₂O

= (2 × 1) + (1 × 16)

= 2 + 16

= 18 g mol⁻¹

🟢 Step 2: Calculate Number of Moles

Number of moles

n = Given Mass ÷ Molar Mass

n = 18 ÷ 18

n = 1 mole

✅ 18 g H₂O = 1 mole H₂O

🟠 Step 3: Calculate Number of Molecules

Number of Molecules = Number of Moles × N_A

= 1 × 6.022 × 10²³

= 6.022 × 10²³ molecules

✅ Number of H₂O molecules = 6.022 × 10²³

Advertisement

🟣 Step 4: Calculate Total Number of Atoms

One molecule of H₂O contains:

2 Hydrogen atoms + 1 Oxygen atom

Total = 3 atoms per molecule

Total Number of Atoms = Number of Molecules × 3

= 6.022 × 10²³ × 3

= 18.066 × 10²³

= 1.8066 × 10²⁴ atoms

✅ Total number of atoms = 1.8066 × 10²⁴

🔬 Atom-wise Calculation

Hydrogen Atoms

2 × 6.022 × 10²³

= 1.2044 × 10²⁴ H atoms

Oxygen Atoms

1 × 6.022 × 10²³

= 6.022 × 10²³ O atoms

🎬 3D-Style H₂O Molecular Animation

One water molecule contains two hydrogen atoms and one oxygen atom.

H O H

1 H₂O molecule = 3 atoms

1 mole H₂O → 6.022 × 10²³ molecules

6.022 × 10²³ molecules → 1.8066 × 10²⁴ atoms

⚡ Quick Shortcut

18 g H₂O
↓
1 mole
↓
6.022 × 10²³ molecules
↓
Each molecule contains 3 atoms
↓
1.8066 × 10²⁴ atoms

✅ Final Answer

Number of molecules = 6.022 × 10²³

Total number of atoms = 1.8066 × 10²⁴

Advertisement

🎯 Formula Revision

Moles = Given Mass ÷ Molar Mass
Molecules = Moles × N_A
Total Atoms = Molecules × Atoms per Molecule

For H₂O → 2 + 1 = 3 atoms per molecule