UPCAT Chemistry Reviewer 2026
12 Chemistry practice questions for the University of the Philippines College Admission Test, each with the correct answer and an explanation of why it's right.
Chemistry Practice Questions with Answers
- 1medium
Different materials have specific gravity values listed. Which material will settle at the bottom if placed in a glass container? [Table: Maple syrup 1.37, Honey 1.36, Light Karo syrup 1.33, Glycerin 1.26, Dishwashing liquid 1.03, Water 1.00, Vegetable oil 0.91, Baby oil 0.82, Rubbing alcohol 0.87, Lamp oil 0.80]
- A.Honey
- B.Lamp oil
- C.Maple Syrup
- D.Rubbing Alcohol
Show answer & explanation
Answer: C. Maple Syrup
The material with the highest specific gravity (densest) sinks to the bottom. Maple syrup (1.37) has the highest SG, greater than honey (1.36).
- 2medium
In a sealed cylinder, a gas was heated. Which of the following will NOT increase?
- A.Average number of gas molecules hitting the cylinder walls per second
- B.Average kinetic energy of the gas molecules
- C.Average speed of the gas molecules
- D.Average distance between the gas molecules
Show answer & explanation
Answer: D. Average distance between the gas molecules
In a sealed, rigid cylinder the volume is constant — so the average distance between gas molecules does not increase. Kinetic energy, speed, and collision frequency all increase with temperature.
- 3medium
Nitrogen molecules are allowed to move randomly in a glass tube. Which figure shows the molecules in a state of greatest entropy? [image of molecule distribution diagrams]
- A.Figure A
- B.Figure B
- C.Figure C
- D.Figure D
Show answer & explanation
Answer: C. Figure C
Step 1: Entropy is a thermodynamic property that measures the randomness or disorder of a system. For gas molecules in a container, entropy increases with greater molecular disorder and more uniform spatial distribution. Step 2: Maximum entropy occurs when molecules are distributed as randomly and uniformly as possible throughout the available space, rather than being clustered together or arranged in ordered patterns. Step 3: Among the given figures, Figure C must show nitrogen molecules distributed most randomly and uniformly throughout the glass tube, representing the highest degree of molecular disorder. Step 4: This random, uniform distribution corresponds to the greatest number of possible molecular arrangements (microstates), which by statistical mechanics principles yields the highest entropy state. Therefore, Figure C shows the molecules in a state of greatest entropy.
- 4medium
Paraquat herbicide has a half-life of 1000 days. Safe soil concentration is 0.028 g/m². What is the shortest time to reach safe levels if current concentration is 1.8 g/m²?
- A.6.43 × 10⁴ days
- B.6.01 × 10³ days
- C.2.14 × 10⁵ days
- D.1.77 × 10³ days
Show answer & explanation
Answer: A. 6.43 × 10⁴ days
Calculation: (1.8 g/m³ ÷ 0.028 g/m²) × 1000 = 64,285.7 ≈ 6.43 × 10⁴ days.
- 5medium
The transfer of heat during conduction flows
- A.From hot to cold
- B.From cold to hot
- C.Both A and B
- D.All of the above
Show answer & explanation
Answer: A. From hot to cold
Heat always flows spontaneously from regions of higher temperature to regions of lower temperature (from hot to cold). This is the second law of thermodynamics.
- 6medium
What is the trend of electronegativity of elements from right to left and from top to bottom?
- A.Increasing, decreasing
- B.Increasing, increasing
- C.Decreasing, decreasing
- D.Decreasing, increasing
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Answer: C. Decreasing, decreasing
Electronegativity decreases from right to left (metals are less electronegative) AND decreases from top to bottom (larger atoms with more electron shielding hold electrons less strongly).
- 7medium
How would you conduct an experiment to separate pigments inside Poinsettia leaves?
- A.Boil the leaves, filter, perform chromatography using the solution.
- B.Boil the leaves, filter, distill the solution.
- C.Boil the leaves, filter, perform centrifugation on the solution.
- D.Boil the leaves, filter, evaporate the solution.
Show answer & explanation
Answer: A. Boil the leaves, filter, perform chromatography using the solution.
Chromatography is the standard technique for separating mixtures of pigments/dyes based on their differing affinities for a stationary phase. Boiling extracts the pigments; filtering removes leaf debris; chromatography separates the individual pigment compounds.
- 8medium
Joey lit 4 identical candles: A under a big jar, B under a medium jar, C under a small jar, D uncovered. Which took the longest to burn?
- A.candle D
- B.candle C
- C.candle B
- D.candle A
Show answer & explanation
Answer: A. candle D
Candle D is uncovered and has unlimited access to oxygen. Combustion requires oxygen; covered candles run out of O₂ and extinguish. Uncovered candle D burns longest.
- 9medium
Water was boiled in a flask with a balloon over the top. The balloon expanded as water boiled. What happened to the weight of the flask and balloon?
- A.It increased as the balloon expanded.
- B.It decreased as the water boiled away.
- C.It stayed the same.
- D.It is unpredictable because the balloon is flexible.
Show answer & explanation
Answer: C. It stayed the same.
By the law of conservation of mass, matter is neither created nor destroyed. The water molecules become steam and inflate the balloon, but they remain inside the sealed system — total mass stays the same.
- 10medium
Kate is wearing perfume on her wrist. Some people smelled her perfume. What is the reason?
- A.Perfume particles spread from higher concentration (wrist) to lower concentration (air).
- B.People can smell concentrated perfume on the wrist but it doesn't travel through air.
- C.Some perfume leaves the wrist and mixes with air particles.
- D.Both A and B.
Show answer & explanation
Answer: A. Perfume particles spread from higher concentration (wrist) to lower concentration (air).
This is diffusion — particles in a gas move randomly and spread from areas of high concentration to low concentration until evenly distributed. The perfume evaporates and diffuses through the air.
- 11medium
Which of the following is a noble gas?
- A.Nitrogen
- B.Oxygen
- C.Neon
- D.Hydrogen
Show answer & explanation
Answer: C. Neon
Noble gases (Group 18) have full valence shells and are chemically stable. Neon (Ne, Z=10) is a noble gas. Nitrogen, oxygen, and hydrogen are reactive nonmetals.
- 12medium
What is the atomic number of carbon?
- A.6
- B.12
- C.8
- D.16
Show answer & explanation
Answer: A. 6
Carbon (C) has atomic number 6, meaning it has 6 protons. Its mass number is approximately 12 (6 protons + 6 neutrons).
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