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Test Prep MCAT Test Exam
Medical College Admission Test: Verbal Reasoning, Biological Sciences, Physical Sciences, Writing Sample (Page 16 )

Updated On: 12-Jan-2026
Page 16 of 164
PDF with 811 Questions

The automobile airbag was designed to inflate upon impact and decrease the risk of injury to drivers and passengers. Among the challenges to its development was the need to find a reliable inflation mechanism that was sufficiently rapid, controllable, and nontoxic. Prototypes employing compressed gases failed to meet these criteriA. Researchers thus turned their attention to chemical alternatives.
The ideal inflatant requires a chemical reaction in which the reactants are stable and relatively dense in the condensed phase while the products are mostly or completely gaseous at ambient temperature and pressure. Additionally, the ideal chemical reaction would require a low activation energy and have a high kinetic rate constant, without the large exothermicity characteristic of most such reactions. Traditional explosives such as nitroglycerin, C3H5N3O9(l), were rejected almost immediately because of the extremely exothermic nature of their conversion. Benign solids such as calcium carbonate, CaCO3 , were similarly rejected, because of their large activation requirements.
The desired attributes were finally found in sodium azide, NaN3, a stable, dense, ionic solid which rapidly decomposes into elemental sodium and nitrogen gas when ignited by an electrical impulse.
2NaN3 2Na + 3N2
Reaction 1
The gas generating mixture includes excess KNO3 which reacts with the sodium metal from Reaction 1 to produce additional N2 and potassium and sodium oxides (Reactions 2 and 3). These oxides react with SiO2 to produce a non-toxic and stable alkaline silica (glass).
10Na + 2KNO3 K2O + 5Na2O + N2
Reaction 2
K2O + Na2O + SiO2 glass
Reaction 3

A sodium azide air bag inflates to a volume of 45 Liters at STP. According to the information contained in the passage, what is the mass of NaN3 (Mol. Wt. = 65) that is required to inflate the bag?

  1. 76 grams
  2. 81 grams
  3. 87 grams
  4. 130 grams

Answer(s): B

Explanation:

According to the passage, each 2 moles of NaN3 ultimately lead to the production of 3.2 moles of N2, 3 moles from Reaction 1 and 1/5 moles from Reaction 2.
2NAN3 3.2N2
A single mole of an ideal gas at STP occupies 22.4 L. Thus, we require 2 moles of gas to occupy about 45L.
Calculating for x, the number of moles of NaN3 required to produce 2 moles of N2:


Now we determine the mass of 1.25 moles by multiplying by the mass of NaN3 (from the periodic table):1.25 moles × (23 + 3(14)) grams/mole = 81.25 grams



The automobile airbag was designed to inflate upon impact and decrease the risk of injury to drivers and passengers. Among the challenges to its development was the need to find a reliable inflation mechanism that was sufficiently rapid, controllable, and nontoxic. Prototypes employing compressed gases failed to meet these criteriA. Researchers thus turned their attention to chemical alternatives.
The ideal inflatant requires a chemical reaction in which the reactants are stable and relatively dense in the condensed phase while the products are mostly or completely gaseous at ambient temperature and pressure. Additionally, the ideal chemical reaction would require a low activation energy and have a high kinetic rate constant, without the large exothermicity characteristic of most such reactions. Traditional explosives such as nitroglycerin, C3H5N3O9(l), were rejected almost immediately because of the extremely exothermic nature of their conversion. Benign solids such as calcium carbonate, CaCO3 , were similarly rejected, because of their large activation requirements.
The desired attributes were finally found in sodium azide, NaN3, a stable, dense, ionic solid which rapidly decomposes into elemental sodium and nitrogen gas when ignited by an electrical impulse.
2NaN3 2Na + 3N2
Reaction 1
The gas generating mixture includes excess KNO3 which reacts with the sodium metal from Reaction 1 to produce additional N2 and potassium and sodium oxides (Reactions 2 and 3). These oxides react with SiO2 to produce a non-toxic and stable alkaline silica (glass).
10Na + 2KNO3 K2O + 5Na2O + N2
Reaction 2
K2O + Na2O + SiO2 glass
Reaction 3

Potassium chlorate, KClO3(s), decomposes when heated, yet it is unsuitable as an airbag inflatant. All of the following characteristics of KClO3 make it a poor candidate for an air bag inflatant EXCEPT:

  1. the decomposition requires a steady supply of energy due to its high activation energy and low exothermicity.
  2. the oxygen gas formed upon decomposition creates a combustion hazard during an automobile accident.
  3. the potassium chloride formed upon decomposition is a dense solid.
  4. the oxygen gas formed upon decomposition leads to rapid expansion of the reaction mixture.

Answer(s): D

Explanation:

D is correct because rapid expansion is a key requirement of any airbag inflatant. The airbag must inflate before the driver and passenger hit the windshield. All the other statements are true and are reasons why potassium chlorate is not suitable as an airbag inflatant.



There are two opposing theories of light: the particle theory and the wave theory. According to the particle theory, light is composed of a stream of tiny particles that are subject to the same physical laws as other types of elementary particles. One consequence of this is that light particles should travel in a straight line unless an external force acts on them. According to the wave theory, light is a wave that shares the characteristics of other waves. Among other things, this means that light waves should interfere with each other under certain conditions.
In support of the wave theory of light, Thomas Young's double slit experiment proves that light does indeed exhibit interference. Figure 1 shows the essential features of the experiment. Parallel rays of monochromatic light pass through two narrow slits and are projected onto a screen. Constructive interference occurs at certain points on the screen, producing bright areas of maximum light intensity. Between these maxima, destructive interference produces light intensity minimA. The positions of the maxima are given by the equation d sin= n, where d is the distance between the slits, is the angle shown in Figure 1, the integer n specifies the particular maxima, and is the wavelength of the incident light. (Note: sin tan for small angles.)


Figure 1
According to the modern theory of light, a beam of light may be described either as a stream of particles or as a wave, depending on the circumstances. Which of the following correctly states a connection between the two descriptions?

  1. The number of light particles that pass by per second is proportional to the frequency of the light wave.
  2. The mass of each particle of light is proportional to the intensity of the light wave.
  3. The size of each particle of light is proportional to the wavelength of the light wave.
  4. The energy of each particle of light is proportional to the frequency of the light wave.

Answer(s): D

Explanation:

A particle of light is known as a photon. You should know the formula E = hf, which states that the energy E of a photon is equal to Planck's constant h times the frequency f of the light. The photon energy is thus proportional to the frequency of the light. Since the photon energy is a property of a particle and frequency is a property of a wave, this relationship successfully connects the particle and wave descriptions of light, and choice D is correct.
Choice A is incorrect because the number of particles passing by per unit time is related to the intensity of the light, not its frequency. Choice B is wrong because photons have zero mass. Choice C is wrong because photons are thought of as point-like particles without size.



There are two opposing theories of light: the particle theory and the wave theory. According to the particle theory, light is composed of a stream of tiny particles that are subject to the same physical laws as other types of elementary particles. One consequence of this is that light particles should travel in a straight line unless an external force acts on them. According to the wave theory, light is a wave that shares the characteristics of other waves. Among other things, this means that light waves should interfere with each other under certain conditions.
In support of the wave theory of light, Thomas Young's double slit experiment proves that light does indeed exhibit interference. Figure 1 shows the essential features of the experiment. Parallel rays of monochromatic light pass through two narrow slits and are projected onto a screen. Constructive interference occurs at certain points on the screen, producing bright areas of maximum light intensity. Between these maxima, destructive interference produces light intensity minimA. The positions of the maxima are given by the equation d sin = n, where d is the distance between the slits, is the angle shown in Figure 1, the integer n specifies the particular maxima, and is the wavelength of the incident light. (Note: sin tan for small angles.)


Light waves can be described in terms of frequency f and wavelength or in terms of wave number k and angular frequency . These quantities are related by the following equations:
= 2/ and = 2f
k
Which equation below accurately describes the speed of the wave v in terms of k and ?

  1. v = f
  2. v = + k
  3. v = /k
  4. v = k

Answer(s): C

Explanation:

You should know that the speed v of a wave is given by v = f, where f is the frequency of the wave, and is its wavelength. This makes sense, since is the distance traveled by the wave in one cycle, and frequency is the inverse of the period, which is the time it takes for one wave to cycle. Now solve the relation in the question stem k = 2/ for to obtain = 2/k. Also solve = 2f for f to obtain f = /2. Substituting these expressions into the speed equation, we obtain v = f = (/2)(2/k) = /k, which is choice C. Choice A, while a correct relation, is not the right answer because it does not express v in terms of and k. Choices B and D can be eliminated on the basis of dimensional analysis because they do not have the units of speed, m/s. k has units of m-1 and has units of s-1, so choice B is nonsensical and choice D has units of 1/(ms).



There are two opposing theories of light: the particle theory and the wave theory. According to the particle theory, light is composed of a stream of tiny particles that are subject to the same physical laws as other types of elementary particles. One consequence of this is that light particles should travel in a straight line unless an external force acts on them. According to the wave theory, light is a wave that shares the characteristics of other waves. Among other things, this means that light waves should interfere with each other under certain conditions.
In support of the wave theory of light, Thomas Young's double slit experiment proves that light does indeed exhibit interference. Figure 1 shows the essential features of the experiment. Parallel rays of monochromatic light pass through two narrow slits and are projected onto a screen. Constructive interference occurs at certain points on the screen, producing bright areas of maximum light intensity. Between these maxima, destructive interference produces light intensity minimA. The positions of the maxima are given by the equation d sin= n, where d is the distance between the slits, is the angle shown in Figure 1, the integer n specifies the particular maxima, and is the wavelength of the incident light. (Note: sin tan for small angles.)


Figure 1
Which of the following is sufficient information to determine the approximate speed of a ray of light in water?

  1. The angle of incidence and the angle of refraction of the light ray as it enters water from air
  2. The wavelength in water and the wavelength in air of the light ray as it enters water from air
  3. The speed of light in a vacuum and the density of water
  4. The speed of light in a vacuum and the index of refraction of water

Answer(s): D

Explanation:

You should know that the speed of light is different in different mediA. The formula associated with this concept is n = c/v, where n is the index of refraction of a given medium, c is the speed of light in a vacuum, and v is the speed of light in the given medium. Hence, if the index of refraction and the speed of light in a vacuum are known, we can solve for the speed of light in the medium. Thus, choice D is correct.
We would need the air's index of refraction, along with the variables in choice A, to calculate the water's index of refraction using Snell's law. Even if we could calculate the water's index of refraction, we would need the speed of light in a vacuum to calculate the speed of light in water, so choice A is wrong. Similarly, the variables in choice B allow the calculation of the index of refraction, but the speed of light is still required so choice B is wrong. Choice C is incorrect because while density might play an indirect role in the index of refraction, the density is not sufficient information to determine the index of refraction.



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