MCAT Question of the Day

Correct Answer: B. 0.1

Use P1V1 = P2V2. Temperature is constant and can be eliminated from the equation. If the volume increases, we know the pressure must decrease. Doubling the volume should then halve the pressure.

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Correct Answer: D. (746 – 24)/760

You must subtract the pressure of water vapor from the total pressure, and change torr to atm. 1 atm = 760 torr = 760 mm Hg.

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Correct Answer: D. (1.00)(0.20)/(0.082)(373)

Use n = PV/RT. Remember R is a constant and that all the units must be converted into atm of pressure, liters of volume, and Kelvin from Celsius.

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Correct Answer: A. C-1

Glucose anomers have a different orientation of the hydroxyl group on the C-1 carbon.

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Correct Answer: A. I only.

At low densities the correction terms to P and V become very small. Both correction terms, nb and an²/V², depend on the number of gas molecules in a given volume, which is small at low densities. PV is not constant for the real gas as it is for an ideal gas.

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Correct Answer: D. Ar < Cl2 < FBr

The order of boiling points corresponds to the strength of intermolecular forces. Argon has the weakest intermolecular forces: as a neutral atom, it is less polarizable than the larger Cl2. The latter has no dipole moment, so it exerts weaker forces than FBr.

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Correct Answer: D. II and III only

Ideal gases do indeed move faster when heated due to the increase in average kinetic energy. However, we assume that there are no intermolecular forces between molecules, therefore they are infinitely compressible in theory. We also assume that an ideal gas will not change into a liquid no matter the conditions.

Correct Answer: B. -OH is a poor leaving group and therefore must be protonated to form a better leaving group, -OH2+.

The hydroxide group is a strong base and therefore a poor leaving group. It must be protonated to form the weak base, H2O, so that it can leave the molecule.

Correct Answer: B. A lower frequency.

A C-O single bond is weaker than a double bond. Therefore, less energy is needed to induce the stretching vibration. Remember reciprocal centimeters is a measure of frequency and energy is directly proportional to the frequency.

Correct Answer: D. Electrophilic substitution.

Substitution reactions are preferred because they preserve the very stable aromatic structure. Electrophiles can join the ring because of the resonance stabilization of the intermediate ion.