EmSAT Chemistry — Questions and Answers
Question 1: What is the atomic number of carbon?
- 12
- 6 (Correct answer)
- 8
- 14
Correct answer: 6
Carbon has atomic number 6, meaning it has 6 protons in its nucleus. The mass number of carbon-12 is 12 (6 protons + 6 neutrons).
Question 2: What type of bond is formed when electrons are shared between two nonmetal atoms?
- Ionic bond
- Covalent bond (Correct answer)
- Metallic bond
- Hydrogen bond
Correct answer: Covalent bond
Covalent bonds form when two nonmetal atoms share electron pairs. Ionic bonds involve electron transfer, typically between metals and nonmetals.
Question 3: What is the pH of a neutral solution at 25°C?
- 0
- 7 (Correct answer)
- 14
- 1
Correct answer: 7
At 25°C, a neutral solution has a pH of 7, where the concentration of H⁺ ions equals the concentration of OH⁻ ions (each at 10⁻⁷ M).
Question 4: How many moles of water are produced when 2 moles of hydrogen gas react with 1 mole of oxygen gas?
- 1 mole
- 2 moles (Correct answer)
- 3 moles
- 4 moles
Correct answer: 2 moles
The balanced equation 2H₂ + O₂ → 2H₂O shows that 2 moles of H₂ reacting with 1 mole of O₂ produces 2 moles of H₂O.
Question 5: Which of the following is an example of a physical change?
- Burning wood
- Rusting iron
- Melting ice (Correct answer)
- Cooking an egg
Correct answer: Melting ice
Melting ice is a physical change because only the state of matter changes (solid to liquid) — the chemical composition (H₂O) remains the same. The other options involve chemical changes.
Question 6: What is the electron configuration of sodium (Na, atomic number 11)?
- 1s² 2s² 2p⁶ 3s¹ (Correct answer)
- 1s² 2s² 2p⁷
- 1s² 2s² 2p⁶ 3s²
- 1s² 2s² 2p⁶ 3p¹
Correct answer: 1s² 2s² 2p⁶ 3s¹
Sodium has 11 electrons, filling orbitals in order: 1s² (2), 2s² (4), 2p⁶ (10), 3s¹ (11), giving the configuration 1s² 2s² 2p⁶ 3s¹.
EmSAT Chemistry
What is the atomic number of carbon?