Chemistry Flashcards

What is the atomic number of carbon?

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).

What type of bond is formed when electrons are shared between two nonmetal atoms?

Answer: Covalent bond

Covalent bonds form when two nonmetal atoms share electron pairs. Ionic bonds involve electron transfer, typically between metals and nonmetals.

What is the pH of a neutral solution at 25°C?

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).

How many moles of water are produced when 2 moles of hydrogen gas react with 1 mole of oxygen gas?

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.

Which of the following is an example of a physical change?

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.

What is the electron configuration of sodium (Na, atomic number 11)?

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.