O-Level Combined Science — Chemistry 2 — Questions and Answers
Question 1: What is the name of the process by which a solid changes directly into a gas?
- Evaporation
- Condensation
- Sublimation (Correct answer)
- Deposition
Correct answer: Sublimation
Sublimation is the process by which a solid changes directly into a gas without passing through the liquid phase, e.g., dry ice (solid CO₂).
Question 2: In electrolysis, where does oxidation occur?
- At the cathode
- In the electrolyte
- At the anode (Correct answer)
- At both electrodes
Correct answer: At the anode
Oxidation occurs at the anode (positive electrode). The mnemonic OIL RIG helps: Oxidation Is Loss; Reduction Is Gain.
Question 3: Which element is represented by the symbol 'Na'?
- Nitrogen
- Nickel
- Sodium (Correct answer)
- Neon
Correct answer: Sodium
'Na' is the chemical symbol for sodium, derived from the Latin word 'Natrium'.
Question 4: What is the empirical formula of a compound with 2 carbon, 6 hydrogen, and 2 oxygen atoms?
- C₂H₆O₂
- CH₃O (Correct answer)
- CHO
- C₂H₆O
Correct answer: CH₃O
Divide all subscripts by the HCF (2): C₂H₆O₂ → CH₃O. The empirical formula is CH₃O.
Question 5: Which gas is used in the Haber Process to make ammonia?
- Oxygen and hydrogen
- Nitrogen and hydrogen (Correct answer)
- Carbon and nitrogen
- Hydrogen and helium
Correct answer: Nitrogen and hydrogen
The Haber Process combines nitrogen (from air) and hydrogen (from natural gas) at high temperature and pressure with an iron catalyst to make ammonia.
Question 6: What colour does litmus paper turn in an acidic solution?
- Blue
- Purple
- Red (Correct answer)
- Yellow
Correct answer: Red
Blue litmus paper turns red in acidic solutions (pH below 7). Red litmus turns blue in alkaline solutions.
O-Level Combined Science — Chemistry 2
What is the name of the process by which a solid changes directly into a gas?