O-Level Combined Science — Chemistry 4 — Questions and Answers
Question 1: What type of isomerism do butane and methylpropane exhibit?
- Geometric isomerism
- Optical isomerism
- Structural isomerism (Correct answer)
- No isomerism
Correct answer: Structural isomerism
Butane (CH₃CH₂CH₂CH₃) and methylpropane ((CH₃)₂CHCH₃) are structural isomers — same molecular formula (C₄H₁₀), different arrangements.
Question 2: Which type of chemical bond is formed when electrons are transferred from one atom to another?
- Covalent bond
- Metallic bond
- Ionic bond (Correct answer)
- Van der Waals force
Correct answer: Ionic bond
Ionic bonds are formed by the transfer of electrons from a metal atom to a non-metal atom, creating oppositely charged ions.
Question 3: What is the test for carbon dioxide gas?
- Burns with a squeaky pop
- Relights a glowing splint
- Turns limewater milky (Correct answer)
- Turns damp litmus paper red
Correct answer: Turns limewater milky
Carbon dioxide turns limewater (calcium hydroxide solution) milky/cloudy due to the formation of calcium carbonate precipitate.
Question 4: In the periodic table, elements in the same group have the same number of:
- Protons
- Neutrons
- Electrons in the outer shell (Correct answer)
- Total electrons
Correct answer: Electrons in the outer shell
Elements in the same group have the same number of electrons in their outermost shell, giving them similar chemical properties.
Question 5: What is produced when ethanol reacts with ethanoic acid?
- Ethyl ethanoate and hydrogen
- Ethyl ethanoate and water (Correct answer)
- Diethyl ether and water
- Ethane and water
Correct answer: Ethyl ethanoate and water
Esterification: ethanol + ethanoic acid → ethyl ethanoate (an ester) + water, in the presence of a concentrated acid catalyst.
Question 6: What is the term for the minimum energy required for a reaction to occur?
- Enthalpy
- Bond energy
- Activation energy (Correct answer)
- Kinetic energy
Correct answer: Activation energy
Activation energy is the minimum energy that colliding particles must possess for a reaction to occur and form products.
O-Level Combined Science — Chemistry 4
What type of isomerism do butane and methylpropane exhibit?