EmSAT EmSAT Chemistry 1 — Questions and Answers
Question 1: What is the electron configuration of oxygen (atomic number 8)?
- 1s² 2s² 2p⁶
- 1s² 2s² 2p⁴ (Correct answer)
- 1s² 2s⁴ 2p²
- 1s² 2s² 2p² 3s²
Correct answer: 1s² 2s² 2p⁴
Oxygen has 8 electrons. The configuration is 1s² 2s² 2p⁴ — 2 in the first shell and 6 in the second shell (2 in 2s and 4 in 2p).
Question 2: What type of bond is formed between Na and Cl in NaCl?
- Covalent bond
- Metallic bond
- Ionic bond (Correct answer)
- Hydrogen bond
Correct answer: Ionic bond
NaCl forms an ionic bond. Sodium (a metal) transfers an electron to chlorine (a non-metal), creating Na⁺ and Cl⁻ ions that attract each other electrostatically.
Question 3: What is Avogadro's number?
- 6.022 × 10²³ (Correct answer)
- 6.022 × 10²⁰
- 3.14 × 10²³
- 1.38 × 10²³
Correct answer: 6.022 × 10²³
Avogadro's number is 6.022 × 10²³, representing the number of particles (atoms, molecules, ions) in one mole of a substance.
Question 4: Balance the equation: H₂ + O₂ → H₂O
- H₂ + O₂ → H₂O
- 2H₂ + O₂ → 2H₂O (Correct answer)
- H₂ + 2O₂ → 2H₂O
- 2H₂ + 2O₂ → 2H₂O
Correct answer: 2H₂ + O₂ → 2H₂O
Balanced: 2H₂ + O₂ → 2H₂O. Left: 4H, 2O. Right: 4H, 2O. Both sides are equal, satisfying conservation of mass.
Question 5: What is the pH of a neutral solution at 25°C?
- 0
- 7 (Correct answer)
- 14
- 1
Correct answer: 7
A neutral solution at 25°C has pH = 7. pH < 7 is acidic, pH > 7 is basic (alkaline). Pure water at 25°C is neutral with pH = 7.
Question 6: What is the molar mass of water (H₂O)?
- 16 g/mol
- 18 g/mol (Correct answer)
- 20 g/mol
- 14 g/mol
Correct answer: 18 g/mol
Molar mass of H₂O = 2(1) + 16 = 18 g/mol. Hydrogen has a molar mass of 1 g/mol and oxygen has 16 g/mol.
EmSAT EmSAT Chemistry 1
What is the electron configuration of oxygen (atomic number 8)?