Practice Test 2 - MCAT Chemical and Physical Foundations of Biological Systems

20 questions. Answer them in any order, then submit to see your score and every explanation.

In a redox-titration validation, a galvanic cell couples the Ce $^{4+}$ /Ce $^{3+}$ couple to the I $_2$ /I $^-$ couple at 25°C using inert Pt electrodes. Standard reduction potentials: $E^\circ$ (Ce $^{4+}$ /Ce $^{3+}$ ) = +1.61 V; $E^\circ$ (I $_2$ /I $^-$ ) = +0.54 V. Based on the setup, which conclusion is most consistent with the electrochemical process?
A peptide chemist attempts to protect a ketone-containing side chain during a multi-step aqueous synthesis. The compound contains a simple ketone (R–CO–R') and is treated with ethylene glycol (excess) and catalytic p-toluenesulfonic acid in toluene under reflux with water removal. The central concept is acetal (ketal) formation via nucleophilic addition to carbonyls. Which product is most likely formed from the reaction described?
A double-slit setup is used to calibrate an optical position sensor in a physics lab. Two narrow slits separated by $d = 0.30\ \text{mm}$ are illuminated by coherent light of wavelength $\lambda = 600\ \text{nm}$ . The interference pattern is recorded on a screen at distance $L = 1.5\ \text{m}$ . The sensor is aligned so that the central bright fringe is at $y=0$ . How would increasing the wavelength to $\lambda = 750\ \text{nm}$ affect the interference pattern on the screen (with $d$ and $L$ held constant)?
In a headspace analysis of volatile anesthetics, a lab compares nitrous oxide (N $_2$ O) to carbon dioxide (CO $_2$ ) as calibration gases. For N $_2$ O, the dominant Lewis structure is typically drawn as N–N–O with a total of 16 valence electrons; for CO $_2$ , the dominant Lewis structure is O=C=O with 16 valence electrons. Both gases are linear under the conditions used. The instrument response is sensitive to molecular polarity because polar analytes interact more strongly with a polar stationary phase. Based on the Lewis structure of N $_2$ O, what prediction can be made regarding its polarity relative to CO $_2$ ? (Electronegativity: N = 3.0, O = 3.5, C = 2.5.)
A lab compares two redox couples in mitochondria: NADH/NAD $^+$ and FADH2/FAD. NADH transfers electrons to the electron transport chain at a higher (more negative) reduction potential difference relative to oxygen than FADH2 does. Assume coupling to ATP synthesis depends on the proton gradient generated. Which statement best describes the relationship between redox potential differences and proton pumping/ATP yield?
A sealed, rigid container holds an ideal gas. Pressure is measured as temperature is varied. The investigator mistakenly uses temperature values in °C directly in proportional reasoning for Gay-Lussac's law. Which statement best identifies the most consistent correction? A. Convert °C to K before applying $\frac{P_1}{T_1}=\frac{P_2}{T_2}$ B. Convert atm to mmHg before applying $\frac{P_1}{T_1}=\frac{P_2}{T_2}$ C. Convert liters to mL before applying $\frac{P_1}{T_1}=\frac{P_2}{T_2}$ D. No conversion is needed because proportionality cancels temperature units
A $0.40\ \text{kg}$ mass attached to a string is swung in a horizontal circle at constant speed. Over one full revolution, the tension force is always perpendicular to the instantaneous displacement. Using the definition of work, which statement is most consistent about the work done by tension over one full revolution?
In a motion-tracking study, a cart moves along a straight, level track. At $t=0\ \text{s}$ its velocity is $+2.0\ \text{m/s}$ . From $t=0$ to $t=3.0\ \text{s}$ , the cart experiences a constant acceleration of $-1.0\ \text{m/s}^2$ (positive is to the right). Which statement best describes the cart's velocity change over this interval?
A sealed glass vial is placed in a beaker of water and sinks. Without opening the vial, a researcher attaches a lightweight foam collar around the vial, increasing the total volume of the vial+collar system with negligible change in total mass. The system is returned to water. Based on Archimedes' Principle, which outcome would be expected?
In a behavioral hearing experiment, two speakers emit the same pure tone ( $f=440\ \text{Hz}$ ) in air ( $v\approx 340\ \text{m/s}$ ). A participant stands at a point where the path length from speaker 1 is 1.00 m and from speaker 2 is 1.386 m; the speakers are driven in phase. Which prediction about wave interaction is most likely at the participant's location?
A technician uses a concave mirror ( $f=10\ \text{cm}$ ) to project an illuminated scale onto a wall for calibration of a motion-tracking setup. The scale is placed $d_o=25\ \text{cm}$ from the mirror. Which prediction about the image is most likely accurate?
An ophthalmic training model uses a single thin converging lens to represent the eye's optical power. The "retina" is a fixed screen $2.0\ \text{cm}$ behind the lens. When viewing a near target at $d_o=25\ \text{cm}$ , the image is observed to fall behind the retina (i.e., the lens is not strong enough). Which change is most consistent with bringing the image onto the retina without moving the retina?
In a simplified model of an axon initial segment, the electric field across a short region is approximately uniform and points from outside to inside. A negatively charged protein domain is transiently free to move. Based on the setup, which outcome is most likely for the direction of the electric force on the protein domain?
In a tissue sample, a lab uses acetic anhydride to acetylate a hydroxyl group on a small molecule (ROH) to form an ester (ROAc). The reaction is performed with a mild base present to neutralize acid byproducts. Which product is most expected as the leaving group from the acetic anhydride during nucleophilic acyl substitution?
In a biomechanics lab, a force plate triggers a sprint start. A runner's center-of-mass velocity along the track is measured as $0\ \text{m/s}$ at the start, then increases to $+4\ \text{m/s}$ over the first second. Which statement best describes the runner's acceleration during that first second?
A student compares the expected boiling points of lactic acid (2-hydroxypropanoic acid) and 1-propanol. Both can hydrogen bond, but one contains both an –OH and a –CO $_2$ H group. Based on intermolecular forces and functional groups, which is expected to have the higher boiling point?
A neuron is modeled (for a brief interval) as a membrane resistance $R_m=100\ \text{M}\Omega$ . A synaptic input produces a transmembrane potential change of $\Delta V=20\ \text{mV}$ across this resistance (assume purely resistive behavior for this question). What membrane current magnitude is most consistent with Ohm's Law?
A metal microelectrode is inserted into tissue, and a redox couple at the surface is modeled by standard reduction potentials. The measured cell potential is approximated by $E_{cell} = E_{cathode} - E_{anode}$ under the same conditions. If the cathode half-reaction becomes less favorable (its reduction potential decreases) while the anode is unchanged, which prediction is most consistent with the model?
To model thiohemiacetal formation in cysteine proteases, a chemist mixes acetone with excess ethanethiol (EtSH) under mildly acidic conditions (catalytic H $^+$ ) in anhydrous solvent. A new product forms that retains the carbonyl carbon but now shows an –OH and –SEt on the same carbon (no oxidation/reduction reagents present). Which species is most consistent with carbonyl nucleophilic addition under these conditions?
A patch-clamp setup approximates a short segment of membrane as a parallel-plate capacitor with fixed plate separation. During an experiment, the membrane potential magnitude $|\Delta V|$ is increased while geometry remains constant. What would be the expected effect of increasing the electric field strength across the membrane segment?

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