HEM103 Comprehensive Exam Review Modules 1–6

CHEM103 Comprehensive Exam
Review Modules 1–6
Module 1: Introduction to Chemistry & Measurements
1. Which of the following is a chemical change?
A) Melting ice
B) Dissolving sugar in water
C) Rusting of iron
D) Boiling water
CORRECT 100% DETAILED ANSR: C) Rusting of iron
Explanation: Chemical changes form new substances with
different properties; rusting iron forms iron oxide.
2. What is the SI unit for mass?
A) Gram
B) Kilogram
C) Liter
D) Meter
CORRECT 100% DETAILED ANSR: B) Kilogram
Explanation: The SI base unit for mass is the kilogram (kg).
3. Convert 2500 mL to liters.
CORRECT 100% DETAILED ANSR: 2.5 L
Explanation: 1 L = 1000 mL, so 2500 ÷ 1000 = 2.5 L.
4. A sample has a mass of 12 g and a volume of 4 cm³.
What is its density?
CORRECT 100% DETAILED ANSR: 3 g/cm³
Explanation: Density = mass ÷ volume = 12 ÷ 4 = 3 g/cm³.
5. Which of these is an extensive property?

, A) Density
B) Mass
C) Temperature
D) Melting point
CORRECT 100% DETAILED ANSR: B) Mass
Explanation: Extensive properties depend on the amount
of substance; mass increases with quantity.


Module 2: Atomic Structure & Periodic Table
6. Who proposed the planetary model of the atom?
A) Dalton
B) Thomson
C) Rutherford
D) Bohr
CORRECT 100% DETAILED ANSR: D) Bohr
Explanation: Bohr proposed electrons orbit the nucleus in
fixed energy levels.
7. How many protons, neutrons, and electrons are in
1123Na^{23}_{11}\text{Na}1123Na?
CORRECT 100% DETAILED ANSR: Protons = 11,
Neutrons = 12, Electrons = 11
Explanation: Atomic number = protons = 11; Mass number
= 23; neutrons = 23 − 11 = 12.
8. Which element is a halogen?
A) Sodium
B) Chlorine
C) Neon
D) Magnesium
CORRECT 100% DETAILED ANSR: B) Chlorine

, Explanation: Halogens are in group 17 (e.g., F, Cl, Br, I,
At).
9. The electron configuration of oxygen is:
A) 1s² 2s² 2p⁴
B) 1s² 2s² 2p⁶
C) 1s² 2s² 2p³
D) 1s² 2s¹ 2p⁵
CORRECT 100% DETAILED ANSR: A) 1s² 2s² 2p⁴
10. Which periodic trend increases across a period?
A) Atomic radius
B) Ionization energy
C) Metallic character
D) Reactivity of alkali metals
CORRECT 100% DETAILED ANSR: B) Ionization energy
Explanation: Ionization energy increases left to right due to
stronger nuclear attraction.


Module 3: Chemical Bonding & Molecular Structure
11. What type of bond is formed when electrons are
shared equally?
A) Ionic
B) Polar covalent
C) Nonpolar covalent
D) Metallic
CORRECT 100% DETAILED ANSR: C) Nonpolar covalent
12. Which molecule has a trigonal planar shape?
A) CH₄
B) BF₃
C) H₂O

, D) NH₃
CORRECT 100% DETAILED ANSR: B) BF₃
13. What is the oxidation state of sulfur in H₂SO₄?
CORRECT 100% DETAILED ANSR: +6
Explanation: Let S = x: 2(+1) + x + 4(−2) = 0 → x = +6
14. Which bond is most polar?
A) C–H
B) O–H
C) N–H
D) C–Cl
CORRECT 100% DETAILED ANSR: B) O–H
15. Which compound exhibits hydrogen bonding?
A) CH₄
B) H₂O
C) CO₂
D) CCl₄
CORRECT 100% DETAILED ANSR: B) H₂O


Module 4: Chemical Reactions & Stoichiometry
16. Balance the equation: _Al+_O2→_Al2O3\_ \text{Al} +
\_
\text{O}_2 → \_
\text{Al}_2\text{O}_3_Al+_O2→_Al2O3 CORRECT
100% DETAILED ANSR: 4 Al + 3 O₂ → 2 Al₂O₃
17. If 5 moles of H₂ react with 2.5 moles of O₂, how
many moles of H₂O are formed?
CORRECT 100% DETAILED ANSR: 5 moles H₂O