MCAT Question of the Day

Correct Answer: C. 6000 N-m

Assuming that the water stream is tangent to the wheel, it will be perpendicular to the radius vector at the point of contact. Therefore, the torque of the force of the water stream is Torque = r*F = (20m)(300 N) = 6000 N-m.

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Correct Answer: D. Boiling and condensation

Melting: solid to liquid and Freezing: liquid to solid occur at the Melting/Freezing Point.
Boiling: liquid to gas and Condensation: gas to liquid occur at the Boiling/Condensation Point.
Both evaporation: liquid to gas at the surface of the liquid and sublimation: solid to gas occur at any temperature.

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Correct Answer: D. pH of the titrant

During a titration procedure, a buret is lowered into a clean Erlenmeyer flask. The initial volume of titrant is recorded and a stream of titrant is delivered while constantly mixing the sample solution. Once the pH indicator changes colors we have reached the endpoint. The final volume is recorded and used in conjunction with the initial volume to find the volume of titrant used, and along with the concentration of the titrant to find how many moles of titrant were used. Finally, we can use stoichiometry of the titration reaction to calculate the number of moles of reactant in our solution. The pH of the titrant is not needed.

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Correct Answer: D. 3.17 x 22.4 = 71.0

STP is Standard Temperature and Pressure or 0^oC and 1 atm pressure. At STP 1 mole of an ideal gas occupies 22.4 L. A good approximation of the molecular mass of a gas is obtained by multiplying its density in g.L^-1 by 22.4 L to attain the mass of 1 mole of gas. Hence: 3.17 x 22.4 = 71.0

24.5 L is the molar volume of an ideal gas under LTP or Laboratory Temperature and Pressure, a balmy 25^oC and 1 atm pressure.

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Correct Answer: C. Part of the innate immune system comprised of plasma proteins synthesized primarily by hepatocytes.

The complement system is a clear example of innate immunity, being a form of host defense that is non-specific and does not adapt in response to antigens. However, there is evidence of cross-talk between the complement system and adaptive immunity. Similarly components of the complement system communicate with components of the inflammatory system and hematopoietic system. Nonetheless, complement system components are distinct from leukocytes and the components of the inflammatory system and are primarilysynthesized in the liver.

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Correct Answer: A. The method relies on the fact that solids are more soluble in a cold solvent than they are in the same amount of hot solvent.

This statement is reversed: The process of recrystallization involves dissolution of the solid in appropriate solvent at a high temperature and the subsequent re-formation of the crystals upon cooling, so that any impurities remain in solution.

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Correct Answer: C. Charles’s gas law

Charles’s Law states: V T
Dalton’s law of Partial Pressures states: Ptotal = P1 + P2 + P3 + …
Boyle’s gas law states: P 1/V
The Ideal gas law states: PV = nRT

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Correct Answer: C. keystone predator

The otter would be considered a SECONDARY consumer, the urchins are the primary consumers, and a hypothetical predator of the otter would be a tertiary consumer. Since the otter is responsible for preventing overgrazing of the small grasses by predating on the out of control urchin population, it is termed a keystone predator that exerts a “top-down” effect on the ecosystem.

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Correct Answer: A. Electric current will only flow from a high potential to a lower potential.

Electric current moves in the direction positive charges move in. Therefore, the electric flow of current flows from the point of higher potential to lower potential, similar to how water falls from the top of the waterfall to the bottom.

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Correct Answer: A. 1-cyclopropyl-4-isopropyl-1,3-dimethylcyclohexane

1. First, identify the (longest) parent chain or cycle -> six carbon ring = “cyclohex”

2. If several substituents are on the ring, they are listed in alphabetical order, and the first substituent is given #1 priority. The cyclohexane has the following substituents: cyclopropyl (#1), 2 methyl groups, iso-propyl (note that iso is not considered when placing in alpha order)

3. Substituents are numbered such one of them is at carbon #1 and the other locations have the lowest possible numbers, going in either a clockwise or counter-clockwise direction, giving the prefix di-, tri-, tetra-, to groups of the same kind (prefixes are not considered when alphabetizing).

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