Tahsili Chemistry — Questions and Answers
Question 1: What is the electron configuration of carbon (atomic number 6)?
- 1s² 2s² 2p⁴
- 1s² 2s² 2p² (Correct answer)
- 1s² 2s¹ 2p³
- 1s² 2p⁴
Correct answer: 1s² 2s² 2p²
Carbon has 6 electrons. Filling in order: 1s² (2 electrons), 2s² (2 electrons), 2p² (2 electrons). Total: 6 electrons. This configuration explains carbon's ability to form 4 covalent bonds.
Question 2: What type of bond forms between sodium (Na) and chlorine (Cl)?
- Covalent bond
- Ionic bond (Correct answer)
- Metallic bond
- Hydrogen bond
Correct answer: Ionic bond
Sodium (metal, low electronegativity) transfers an electron to chlorine (non-metal, high electronegativity), forming Na⁺ and Cl⁻ ions. The electrostatic attraction between these oppositely charged ions is an ionic bond.
Question 3: What is the pH of a solution with a hydrogen ion concentration of 10⁻³ M?
- 3 (Correct answer)
- 11
- -3
- 7
Correct answer: 3
pH = -log[H⁺] = -log(10⁻³) = -(-3) = 3. A pH of 3 is acidic (pH < 7). The pH scale measures acidity/basicity logarithmically.
Question 4: Balance the equation: __Fe + __O₂ → __Fe₂O₃
- 2Fe + O₂ → Fe₂O₃
- 4Fe + 3O₂ → 2Fe₂O₃ (Correct answer)
- Fe + O₂ → Fe₂O₃
- 3Fe + 2O₂ → Fe₃O₂
Correct answer: 4Fe + 3O₂ → 2Fe₂O₃
Balanced: 4Fe + 3O₂ → 2Fe₂O₃. Check: Fe: 4 = 2×2 = 4 ✓. O: 3×2 = 6 = 2×3 = 6 ✓. Both sides have equal atoms of each element.
Question 5: What is Avogadro's number and what does it represent?
- 3.14 × 10²³ — the number of protons in a mole
- 6.022 × 10²³ — the number of particles in one mole of a substance (Correct answer)
- 1.6 × 10⁻¹⁹ — the charge of an electron
- 9.8 — the acceleration due to gravity
Correct answer: 6.022 × 10²³ — the number of particles in one mole of a substance
Avogadro's number (6.022 × 10²³) is the number of atoms, molecules, or particles in one mole of any substance. It connects the atomic/molecular scale to the macroscopic scale, enabling conversion between mass and number of particles.
Question 6: What is the molar mass of water (H₂O)?
- 16 g/mol
- 18 g/mol (Correct answer)
- 20 g/mol
- 2 g/mol
Correct answer: 18 g/mol
Molar mass of H₂O = 2(H) + 1(O) = 2(1.008) + 16.00 = 2.016 + 16.00 ≈ 18 g/mol. Molar mass is the mass of one mole of molecules, calculated by summing atomic masses of all atoms in the formula.
Tahsili Chemistry
What is the electron configuration of carbon (atomic number 6)?