Chem/Phys

Question 1

Molarity (Definition and Equations)

Answer 1

Definition: Number of moles of solute per liter of solution
1M= 1mol/L

Question 2

Avogadro’s Number

Answer 2

6.02x10^23

Question 3

Colligative Properties

Answer 3

These properties depend on the number of solute particles present. They are vapor pressure reduction, boiling point elevation, freezing point reduction, and osmotic pressure.

Question 4

Adding salt to water causes the boiling point of water to?

Answer 4

Increase, requiring a greater average kinetic energy of the liquid to produce a vapor pressure equal to the external pressure. Consistent with colligative effects, adding solute to water raises boiling point and lowers melting point.

Question 5

Beta-minus decay

Answer 5

Emission of an electron. Can also be thought of as transition of a neutron to a proton.

Question 6

Separation Techniques

Answer 6

Distillation, Recrystallization, Chromatography, Centrifugation. (Chem/Ochem Ch. 12, Biochem Ch 5)

Question 7

Boiling chips and vacuum distillation, respectively, are used in distillations to:

Answer 7

Boiling chips provide a site for gas bubbles to form, thereby preventing superheating of the liquid or solution. Vacuum distillation lowers the pressure inside of the distillation flask, which lowers the boiling point of a liquid or solution that would otherwise be difficult to distill.

Question 8

The liquid remaining in the homogeneous mixture at the end of the distillation procedure was most likely: 2-methylundecanal or 2-methylundecanoic acid?

Answer 8

2-methylundecanoic acid
In distillation procedures, the component with the lower boiling point vaporizes first, leaving the remaining components in the original flask. Thus, this question is asking which component has the higher boiling point. The aldehyde does not hydrogen-bond but the carboxylic acid forms strong hydrogen bonds with its CO2H, so the aldehyde would be more volatile and the carboxylic acid would remain in the flask. The boiling points of the aldehyde and carboxylic acid are 170°C and 300°C, respectively.

Question 9

Torque is___

Answer 9

Torque (τ) is the rotational analog of force.
Torque can be defined as τ = F∙d∙sin(θ), where F is the force applied, d is the distance that the force is applied from the fulcrum, and θ is the angle between the lever arm and the force that is applied.
Three ways to increase the torque applied to an object: (1) increasing the force, (2) increasing the distance at which the force is applied from the fulcrum, and (3) adjusting the angle at which the force is applied to make it as close as possible to perpendicular to the lever arm.

Question 10

If a 90-kg man undergoes a turning acceleration of 5 m/s2 during a running turn, what is the magnitude of force experienced by the foot due to the ground?

Answer 10

We are looking for the overall force experienced, so we must find the vector sum, or the hypotenuse. Specifically, we need to find the hypotenuse of a triangle with legs of Fnormal = mg = (90 kg)(10 m/s2) = 900 N, and Fturning = (90 kg)(5 m/s2) = 450 N. The combined vector will be larger in magnitude than either component alone, so eliminate choices A and B. To solve, calculate as follows:

Fcombined = [(Fnormal)2 + (Fturning)2]½

Question 11

How do competitive inhibitors change Km and Vmax?

Answer 11

Km values increase
Vmax values remain unaltered

Question 12

A book rests horizontally on a table. The book experiences a gravitational force of mg due to Earth’s gravity. According to Newton’s third law, what is the corresponding reaction force:

Answer 12

The earth experiences a gravitational force of mg from the book.

Newton’s third law can be expressed as:
FA on B = −FB on A

Here, the force of the earth (A) pulling down on the book (B) is equal and opposite to the force of the book (B) pulling up on the earth (A).

Question 13

Nitrogen is primarily present in the atmosphere as a diatomic gas. Which of the following is true about this form of nitrogen?

Answer 13

Diatomic nitrogen gas is relatively inert and can be used in the atmosphere in laboratory reactions to prevent unwanted side reactions.

Question 14

What is the structure of Acetone?

Answer 14

CH3-C(-O)-CH3

Acetone’s central carbon is sp2 hybridized. It has a bond angle of 12o degrees.

Question 15

Simple power equations

Answer 15

P= IV
P=I^2R
P=V^2/R

Power is in Watts

Question 16

A circuit is constructed with a 12-V battery and four identical resistors, each with a resistance of 16 Ω, and connected in parallel. What is the total power dissipated by the circuit?

Answer 16

The question asks us to solve for power, which is measured in watts. Choices B and C have the wrong units (J) and can be immediately eliminated. To choose between the remaining answers, we must use one of the three simple power equations: P = IV, P = I2R, or P = V2/R. These equations are all derived from Ohm’s law, so any one of these equations can be chosen, depending on the situation. We are given voltage, and we can solve for resistance. For a circuit in parallel:

1/Rtot = 1/R1 + 1/R2 + 1/R3 + 1/R4

1/Rtot = 1/16Ω + 1/16Ω + 1/16Ω + 1/16Ω

1/Rtot = 4/16Ω = 1/4Ω

Rtot = 4Ω

Next, we must solve for power: P = V2/R = (12 V)2/4Ω = 144 V2/4Ω = 36 W

Question 17

LiAlH4

Answer 17

Reducing agent capable of reducing an aldehyde to a primary alcohol. This does not reduce alkenes to alkanes, such as H2 with Pd does.

Question 18

Given information provided in the passage, which of the following is the most likely standard voltage change for the ½ O2/H2O redox pair?

Answer 18

+0.82 V

In the electron transport chain, electrons are passed from species with a less positive reduction potential to those with a more positive reduction potential. O2 serves as the final electron acceptor of the electron transport chain and must possess a standard reduction potential that is more positive than any other acceptor in the chain. Of the standard reduction potentials mentioned in the passage, the greatest is that of Fe3+/ Fe2+ in cytochrome c, for which E° = +0.22 V. Only choice A exceeds this value.

Question 19

The angle of incidence is always equal to what other angle?

Answer 19

The angle of reflection

Question 20

Which of the following correctly describes the orbital hybridization of XeF4 and NH3, respectively?

Answer 20

sp3d2, sp3

Question 21

What is Keq?

Answer 21

Equilibrium constant for the dissociation reaction.
Formulas:
Keq=conc of products/conc of reactants
Keq=1/Ka

Question 22

According to the experimental procedure, which of the following describes the physical properties of indium tin oxide?

I. Opaque
II. Electrically conducting
III. Solid at standard temperature

Answer 22

II and III only
The second paragraph of the passage states that the solution was then spread on the conductive faces of two transparent glass plates coated with indium tin oxide (ITO). The word “conductive” refers to electrical conductivity, and since the device is connected to a current generator, choice II is correct (eliminate B and C). Additionally, the plates are described as solid objects. Furthermore, both indium and tin are metals, and the vast majority of metal oxides are solids at standard temperature. Unless told otherwise by the MCAT, we can assume that experiments take place at or near standard conditions, making choice III also correct.