The number of neutrons in 1.7g of ammonia (NH₃) is 4.215 × 10²³. Ammonia (NH₃) has a molar mass of 17 g/mol. In each NH₃ molecule, there are 7 neutrons (all from the nitrogen atom; hydrogen-1 has 0 neutrons). The calculation uses Avogadro's number (6.022 × 10²³).
1.7g of NH₃ = 0.1 mol (molar mass of NH₃ = 17 g/mol).
0.1 mol NH₃ = 6.022 × 10²² molecules.
Each NH₃ molecule has 7 neutrons (7 from N, 0 from each H).
Total neutrons in 1.7g NH₃ = 4.215 × 10²³.
Neutrons in N = 14 – 7 = 7; neutrons in ¹H = 1 – 1 = 0.
Avogadro's number = 6.022 × 10²³ mol⁻¹.
Given: Mass of NH₃ = 1.7 g
Step 1 — Molar Mass of NH₃: • N: 14 g/mol, H: 1 g/mol × 3 = 3 g/mol • Molar mass of NH₃ = 14 + 3 = 17 g/mol
Step 2 — Moles of NH₃: • Moles = Mass ÷ Molar Mass • Moles = 1.7 ÷ 17 = 0.1 mol
Step 3 — Number of Molecules: • Molecules = Moles × Avogadro's Number • Molecules = 0.1 × 6.022 × 10²³ = 6.022 × 10²² molecules
Step 4 — Neutrons per NH₃ Molecule: • Nitrogen (¹⁴N): atomic number 7, mass number 14 → Neutrons in N = 14 – 7 = 7 neutrons • Hydrogen (¹H): atomic number 1, mass number 1 → Neutrons in H = 1 – 1 = 0 neutrons • 3 H atoms: 3 × 0 = 0 neutrons • Total neutrons per NH₃ = 7 + 0 = 7 neutrons
Step 5 — Total Neutrons: • Total neutrons = Molecules × Neutrons per molecule • Total neutrons = 6.022 × 10²² × 7 • Total neutrons = 4.2154 × 10²³ ≈ 4.215 × 10²³
Answer: Number of neutrons in 1.7g NH₃ = 4.215 × 10²³
Summary Table:
| Step | Value |
|---|---|
| Molar mass of NH₃ | 17 g/mol |
| Moles of NH₃ | 0.1 mol |
| Molecules of NH₃ | 6.022 × 10²² |
| Neutrons per molecule | 7 |
| Total neutrons | 4.215 × 10²³ |
Key Concepts: • Avogadro's number: 6.022 × 10²³ mol⁻¹ • Neutrons = Mass number – Atomic number • Hydrogen-1 (protium) has 0 neutrons • This type of question appears in NCERT Class 11 Chemistry — Some Basic Concepts of Chemistry
1.7g NH₃ contains 4.215 × 10²³ neutrons. Calculation: Molar mass of NH₃ = 17 g/mol; moles = 1.7÷17 = 0.1 mol; molecules = 0.1 × 6.022×10²³ = 6.022×10²². Each NH₃ has 7 neutrons (7 from N, 0 from each H-1 atom). Total = 6.022×10²² × 7 = 4.215×10²³.
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