MCAT (Chemical and Physical Foundations) 2 — Questions and Answers
Question 1: A buffer solution contains 0.10 M acetic acid and 0.15 M sodium acetate (pKa = 4.76). What is the pH of this buffer?
- 4.58
- 4.76
- 4.94 (Correct answer)
- 5.12
Correct answer: 4.94
Using Henderson-Hasselbalch: pH = 4.76 + log(0.15/0.10) = 4.76 + 0.18 = 4.94.
Question 2: Which quantum number determines the shape of an atomic orbital?
- Principal quantum number (n)
- Angular momentum quantum number (l) (Correct answer)
- Magnetic quantum number (ml)
- Spin quantum number (ms)
Correct answer: Angular momentum quantum number (l)
The angular momentum quantum number (l) defines the shape of an orbital (s, p, d, f).
Question 3: A 70 kg person stands on a scale in an elevator accelerating upward at 2 m/s². What does the scale read? (g = 10 m/s²)
- 560 N
- 700 N
- 840 N (Correct answer)
- 980 N
Correct answer: 840 N
Apparent weight = m(g + a) = 70(10 + 2) = 840 N.
Question 4: Which of the following molecules has the highest boiling point?
- CH4
- NH3 (Correct answer)
- PH3
- SiH4
Correct answer: NH3
NH3 has the highest boiling point due to hydrogen bonding between molecules, which requires more energy to overcome.
Question 5: An ideal gas undergoes an isothermal expansion. Which thermodynamic statement is correct?
- ΔU > 0 and q < 0
- ΔU = 0 and w < 0 (Correct answer)
- ΔU = 0 and q < 0
- ΔU < 0 and q > 0
Correct answer: ΔU = 0 and w < 0
In isothermal expansion of an ideal gas, ΔU = 0 (temperature constant), and the gas does positive work on surroundings (w < 0 in sign convention where w = work done on system).
Question 6: A wave has a frequency of 500 Hz and travels at 340 m/s in air. What is its wavelength?
- 0.47 m
- 0.68 m (Correct answer)
- 1.47 m
- 170 m
Correct answer: 0.68 m
Wavelength = v/f = 340/500 = 0.68 m.
Question 7: In a galvanic cell, which statement correctly describes electrode behavior?
- Oxidation occurs at the cathode; electrons flow toward the anode
- Reduction occurs at the anode; cations migrate toward the anode
- Oxidation occurs at the anode; electrons flow toward the cathode (Correct answer)
- Reduction occurs at the cathode; anions migrate toward the anode through the external circuit
Correct answer: Oxidation occurs at the anode; electrons flow toward the cathode
In a galvanic cell, oxidation occurs at the anode (releasing electrons) and electrons flow through the external circuit to the cathode where reduction occurs.
MCAT (Chemical and Physical Foundations) 2
A buffer solution contains 0.10 M acetic acid and 0.15 M sodium acetate (pKa = 4.76).
What is the pH of this buffer?