MCAT (Chemical and Physical Foundations) 4 — Questions and Answers
Question 1: Light travels from glass (n = 1.5) into water (n = 1.33). What is the critical angle for total internal reflection?
- 48.2°
- 52.5°
- 62.5° (Correct answer)
- 69.7°
Correct answer: 62.5°
sin(θc) = n₂/n₁ = 1.33/1.5 = 0.887; θc = arcsin(0.887) ≈ 62.5°.
Question 2: Which of the following has the highest electron affinity?
- Na
- Cl (Correct answer)
- Ar
- K
Correct answer: Cl
Chlorine has the highest electron affinity among these elements because gaining one electron completes its valence shell with minimal electron-electron repulsion.
Question 3: A 0.5 mol sample of an ideal gas occupies 11.2 L at STP. If the temperature is doubled at constant pressure, what is the new volume?
- 5.6 L
- 11.2 L
- 22.4 L (Correct answer)
- 44.8 L
Correct answer: 22.4 L
By Charles's Law, V₁/T₁ = V₂/T₂; doubling T at constant P doubles V: 11.2 × 2 = 22.4 L.
Question 4: In a second-order reaction, when the initial concentration of reactant is doubled, what happens to the half-life?
- It doubles
- It quadruples
- It is halved (Correct answer)
- It remains unchanged
Correct answer: It is halved
For a second-order reaction, t½ = 1/(k[A]₀); doubling [A]₀ halves the half-life.
Question 5: Which property of sound waves increases when the medium's temperature rises?
- Frequency
- Wavelength in a constant-frequency wave only
- Speed (Correct answer)
- Amplitude
Correct answer: Speed
Sound speed in a gas increases with temperature because molecules move faster, transmitting vibrations more quickly.
Question 6: An atom has the electron configuration [Ar] 3d⁵ 4s¹. Which element is this?
- Vanadium (V)
- Manganese (Mn)
- Chromium (Cr) (Correct answer)
- Iron (Fe)
Correct answer: Chromium (Cr)
Chromium (Z=24) has the anomalous configuration [Ar] 3d⁵ 4s¹ due to the extra stability of a half-filled d subshell.
Question 7: A solution is prepared by dissolving 0.1 mol NaCl in 1 kg of water. What is the expected freezing point? (Kf water = 1.86°C/m)
- –0.186°C
- –0.372°C (Correct answer)
- –0.093°C
- –0.744°C
Correct answer: –0.372°C
NaCl dissociates into 2 ions, so i = 2; ΔTf = iKfm = 2 × 1.86 × 0.1 = 0.372°C depression.
MCAT (Chemical and Physical Foundations) 4
Light travels from glass (n = 1.5) into water (n = 1.33).
What is the critical angle for total internal reflection?