MCAT (Chemical and Physical Foundations) 5 — Questions and Answers
Question 1: A fluid flows through a pipe that narrows from a cross-sectional area of 0.04 m² to 0.01 m². If the velocity in the wide section is 2 m/s, what is the velocity in the narrow section?
- 0.5 m/s
- 4 m/s
- 8 m/s (Correct answer)
- 16 m/s
Correct answer: 8 m/s
By the continuity equation, A₁v₁ = A₂v₂: 0.04×2 = 0.01×v₂; v₂ = 8 m/s.
Question 2: Which of the following statements about Le Chatelier's principle is correct when pressure is increased on the equilibrium N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?
- Equilibrium shifts left to produce more moles of gas
- Equilibrium shifts right to produce fewer moles of gas (Correct answer)
- Equilibrium is unaffected because the reaction involves only gases
- Equilibrium shifts right because ammonia is the product
Correct answer: Equilibrium shifts right to produce fewer moles of gas
Increasing pressure favors the side with fewer moles of gas; 4 moles of reactant gas form 2 moles of NH₃, so equilibrium shifts right.
Question 3: Which of the following correctly describes a diamagnetic species?
- It contains unpaired electrons and is attracted to a magnetic field
- It contains only paired electrons and is weakly repelled by a magnetic field (Correct answer)
- It contains unpaired electrons and is repelled by a magnetic field
- It contains only paired electrons and is strongly attracted to a magnetic field
Correct answer: It contains only paired electrons and is weakly repelled by a magnetic field
Diamagnetic species have all electrons paired; they experience weak repulsion in a magnetic field because paired electrons cancel each other's magnetic moments.
Question 4: A converging lens with focal length 10 cm forms an image of an object placed 30 cm away. Where is the image located?
- 5 cm on the same side as the object
- 15 cm on the opposite side (Correct answer)
- 20 cm on the opposite side
- 30 cm on the opposite side
Correct answer: 15 cm on the opposite side
Using 1/f = 1/do + 1/di: 1/10 = 1/30 + 1/di; di = 15 cm on the opposite side (real image).
Question 5: Which type of radioactive decay results in a product with the same mass number but a different atomic number?
- Alpha decay
- Beta decay (Correct answer)
- Gamma decay
- Positron emission
Correct answer: Beta decay
Beta decay converts a neutron to a proton (or vice versa), changing Z by ±1 while mass number A remains constant.
Question 6: At constant temperature, if the pressure of an ideal gas is tripled, the volume becomes:
- One-ninth of the original
- One-third of the original (Correct answer)
- Three times the original
- Nine times the original
Correct answer: One-third of the original
Boyle's Law: P₁V₁ = P₂V₂; tripling pressure reduces volume to one-third at constant temperature.
Question 7: Which factor most directly determines the formal charge of an atom in a Lewis structure?
- The number of lone pairs minus the number of bonds
- The difference between valence electrons and (lone pair electrons + half of bonding electrons) (Correct answer)
- The difference between atomic number and number of bonds
- The electronegativity of the atom relative to bonded atoms
Correct answer: The difference between valence electrons and (lone pair electrons + half of bonding electrons)
Formal charge = valence electrons – lone pair electrons – ½(bonding electrons).
MCAT (Chemical and Physical Foundations) 5
A fluid flows through a pipe that narrows from a cross-sectional area of 0.04 m² to 0.01 m².
If the velocity in the wide section is 2 m/s, what is the velocity in the narrow section?