IB myp 4-5 Chemistry – Practice Questions- All Topics
Topic :The atmosphere -Testing and Treatment
Topic :The atmosphere- Weightage : 21 %
All Questions for Topic : Characteristics of gases,Atmospheric composition,Testing and Treatment,Extraction,Emission and environmental Implications
Question (12 marks)
Aerosol deodorant sprays use compressed gas to spray scent onto your skin.
Question a (2 marks)
Deodorants release gases into the air. Use the diagram below to state the two most common gases in the atmosphere and their percentages.
Atmospheric Composition:
- Nitrogen: 78%
- Oxygen: 20.9%
- Argon: 0.9%
- Carbon dioxide: 0.03%
- Other gases: 0.17%
Gas 1: Percentage: %
Gas 2: Percentage: %
▶️Answer/Explanation
Answer: Nitrogen (78%), Oxygen (20.9%)
Explanation: Earth’s atmosphere is primarily composed of nitrogen (N2) and oxygen (O2), which together make up about 99% of dry air.
Atmospheric Science: The nitrogen cycle maintains atmospheric N2, while oxygen is replenished through photosynthesis. These percentages remain relatively constant in the lower atmosphere.
Question b (3 marks)
Most gases in the atmosphere are diatomic or polyatomic. Noble gases are monatomic. Complete the table below:
| Type of Gas | Example |
|---|---|
▶️Answer/Explanation
Answer:
| Monatomic gas | Helium |
| Diatomic gas | Oxygen |
| Polyatomic gas | Carbon dioxide |
Explanation: Noble gases like helium exist as single atoms (monatomic). Most elements like oxygen form diatomic molecules. Compounds like CO2 are polyatomic.
Molecular Structure: The number of atoms in gas molecules affects their properties – monatomic gases are generally less reactive, while polyatomic gases often participate in chemical reactions.
Question c (1 mark)
State a reason why noble gases are found naturally as monatomic gases.
▶️Answer/Explanation
Answer: Noble gases have full outer electron shells, making them chemically stable and unreactive.
Explanation: Their complete valence shells (octet for all except helium which has a duplet) mean they don’t need to share or transfer electrons with other atoms.
Chemical Stability: This full outer shell configuration gives noble gases high ionization energies and positive electron affinities, making bond formation energetically unfavorable.
Question d (2 marks)
Aerosol sprays used to contain CFCs like Freon® (trichlorotrifluoroethane, C2Cl3F3). Calculate its relative molecular mass.
Atomic masses: C=12, Cl=35.5, F=19
▶️Answer/Explanation
Answer: 187.5
Calculation: (2×12) + (3×35.5) + (3×19) = 24 + 106.5 + 57 = 187.5
Method: Sum the atomic masses of all atoms in the molecule: two carbon (24), three chlorine (106.5), and three fluorine atoms (57).
Question e (3 marks)
Deodorant scent diffuses through air. Explain why diffusion is slower at 4°C than at 20°C using particle theory.
▶️Answer/Explanation
Answer: At lower temperatures, gas particles have less kinetic energy, move slower, and collide less frequently, resulting in slower diffusion.
Detailed Explanation: 1. Temperature measures average kinetic energy of particles 2. At 4°C vs 20°C, particles have ≈6% less kinetic energy (277K vs 293K) 3. Lower energy means slower random motion (Brownian motion) 4. Diffusion depends on particle speed and collision frequency 5. Fewer collisions per second at lower temperatures 6. Therefore scent molecules take longer to spread through the room
Scientific Principle: This demonstrates the Maxwell-Boltzmann distribution – at lower temps, fewer particles have sufficient energy to overcome activation barriers for movement.
Question f (1 mark)
CFCs were replaced with propane (C3H8). Draw its structure.
▶️Answer/Explanation
Answer: H H H \ | / C-C-C / | \ H H H
Explanation: Propane is a straight-chain alkane with three carbon atoms single-bonded together, each fully saturated with hydrogen atoms.
Structural Chemistry: The tetrahedral geometry around each carbon atom gives propane its characteristic structure, with bond angles of approximately 109.5°.