AAMC MCAT test 3r a

When this sequence is applied to the question, answer choice B is in the correct order, and answers A, C, and D are all in the opposite order.. The melting point of acetamide is 80oC; th

Detailed answers to practice test 3R by AAMC

Physical Science Part 1-77

1. Reaction 4 is shown in the following equation, which is answer choice A

Answers B and D do not show a reaction involving PbCO3 (s), as required by Reaction 4 Answer C shows an implausible and unbalanced equation Thus, answer choice A is the best answer

At pH 9, the concentration of OH-(aq) is greater than the concentration of OH-(aq) at pH 7 According to Le

Châtelier's principle, the additional common ion, OH-(aq ), will shift the position of equilibrium to the left, and less Pb(OH)2 will dissolve Thus, answer choice A is the best answer

4. The reactions described in the passage show that lead(II) is successively precipitated as PbSO4, PbI2 , and PbCO3 This sequence shows (assuming equal anion concentrations, as must be done here) that PbCO3 is less soluble than PbI2 , and PbI2 is less soluble than PbSO4 The order in which the anions precipitate Pb2+ is: CO32- then I- then SO42- When this sequence is applied to the question, answer choice B is in the correct order, and answers A, C, and D are all in the opposite order Thus, answer choice B is the best answer

8. Polar water molecules are held together by relatively strong hydrogen bonds; whereas, the linear, nonpolar molecules of CO2 are held together at room temperature by weak London dispersion forces Thus, answer choice D is the best answer

11. The emission peaks P1 and P2 are described in the passage as due to an electron from an outer energy level filling a vacant inner energy level, resulting in emission of an X-ray photon These photons have discreteenergies, and therefore discrete wavelengths, so they appear in the spectrum as peaks Thus, answer choice C

is the best answer

12. The power P , supplied by the battery to accelerate the electron beam is given by the formula P = I

·V , where I is the beam current and V is the potential difference between the cathode and anode Therefore P = (5 x 10-3 A) x (105 V) = 5 x 102 W

Therefore, answer choice A is the best answer

13. The emitted X- ray has the positive energy difference between the atomic energy levels as measured bytheir ionization potentials For Pb n = 2 to 1, that is (1,400 x 10-17 J) - (240 x10-17 J) = 1160 x 10-17 J = 1.16 x 10-14 J Thus, answer choice C is the best answer

correct answer

15. To increase the kinetic energy of the electrons, they must be accelerated by a higher voltage between the cathode and anode, thus the voltage of HV was increased Thus, answer choice A is the best answer

16. The probability of an X-ray emission event at a given wavelength is measured by its intensity in the spectrum In Figure 2, P2 has a higher intensity than does P1 Thus, answer choice D is the best answer

17. The dipole moment of a molecule is the vector sum of all of the bond moments According to the data

in Table 1, the dipole moment of SnBr4 is zero; therefore, its bond moments add to zero or cancel Thus, answer choice D is the best answer

20. HCl is polar covalent because H and Cl share a pair of bonded electrons that are more strongly attracted

to the chlorine atom The higher effective nuclear charge (i.e., the charge of the nucleus minus the shielding caused by extranuclear electrons) of chlorine accounts for its greater electronegativity Thus, answer choice D

is the best answer

21. Carbon dioxide, O=C=O, is linear Therefore, the two CO dipoles cancel because they are in opposite directions If one of the oxygen atoms is removed, the resulting CO will have a dipole because the species is linear and comprised of two different atoms Thus, the dipole moment will change from zero in CO2 to a positive value in CO Thus, answer choice D is the best answer

22. An analysis of the two structures shows that the bond moments in PCl5 add to zero; whereas, those in PCl3 do not As shown in the figure, PCl3 is pyramidal not planar Thus, answer choice B is the best answer

23. Work is the product of the force on an object and the distance the object moves in the direction of the applied force In this case, work = 20 N x 10 m = 200 J Thus, answer choice C is the best answer

24. Evaporation occurs when a molecule attains sufficient speed or kinetic energy to overcome the

attractive forces of a liquid Resonance, surface tension and potential energy all relate to molecules that are not in motion Thus, answer choice B is the best answer

sin2θ =F2=4 2 + 3 2=25N2

Therefore F=5N The F vector points in the proper direction since tanθ =0.75= 3/4

Thus, answer choice C is the best answer

27. The only experimental difference in Trial 1 vs Trial 2 is that, in Trial 2, the test tube is placed in water (20oC) to cool rather than in air (also 20oC) In other words, only the surroundings were different Thus, answer choice B is the best answer

28. The melting point of acetamide is 80oC; therefore, acetamide will melt when it is in a test tube that is placed in a water bath at 90oC The temperature of the water in the bath, not the amount of water in the bath, determines whether or not the acetamide will melt The period of time for acetamide to melt, starting at 90oC,

is more than the corresponding period, starting at 100oC (i.e., the temperature of boiling water) Thus, answer choice D is the best answer

29. Without controlling the temperature (i.e., raising the temperature of the water bath above 80oC), the experimenter could not have observed melting or freezing Without monitoring the time, the experimenter could not have determined the period of time for the samples to melt or freeze The temperature of melting (freezing) of a pure substance such as acetamide is independent of the amount melted, and Experiment 2 shows that the surroundings control the period of time for freezing to occur Thus, answer choice A is the bestanswer

30. The time period of melting is independent of the time intervals used by the experimenter to record temperatures The sample would freeze completely after 23 min regardless of the time interval used by the experimenter to record temperatures Thus, answer choice B is the best answer

33. The tone with the shortest period has the shortest wavelength In Figure 1a, the period of the third harmonic (the curve with the smaller dashes) is seen to be shorter than the other two harmonics Thus, answer choice C is the best answer

34. The three curves in Figure 1a intersect at three points in time The second intersection occurs in the middle of the time axis At that point all three curves have zero displacement Therefore, answer choice C is the best answer

35. The period T and frequency f of a tone are related by T=1/ f If the first harmonic has a frequency of

100 Hz, then the second harmonic has a frequency of 200 Hz The period corresponding to 200 Hz is 1/200 s

-1=0.005 s Thus, answer choice A is the best answer

36. The amplitudes of the three harmonics can be compared in Figure 1a The first harmonic is seen to be largest while the other two have equal amplitudes Answer choice A best represents these observations

38. The waveform in Figure 1c begins to repeat at the zero displacement point near the end of the time axis This is the same time period as the first harmonic as seen in Figure 1a Thus, answer choice A is the best answer

39. The relation of wavelength, frequency, and wave velocity is λ ·f=v For light, v=3 x 108m/s The wavelength for Material B at an efficiency of 0.42 is read from Table 1 as λ =1.06 x 10-6m The frequency of this light is 3 x 108 m/s divided by 1.06 x 10-6 m, giving 2.8 x 1014Hz Thus, answer choice C is the best answer

43. Applying a coating that makes ε independent of the wavelength means ε is the same for all λ Thus,

ε is constant when plotted versus λ , a horizontal line Therefore, answer choice C is the best answer

44. According to the data in Table 1, both structure and molecular weight (i.e., molar mass) affect the melting point of a compound In order to assess the effect of molecular weight or mass alone, any other effectssuch as obvious structural differences must be minimized This is best done by comparing two compounds that are structurally similar Because the structures of propionic acid and butyric acid (Answer C) differ by only a CH2 group, they best show that melting point increases with molar mass All of the other answer choices compare two compounds that differ significantly in structure Therefore, the melting points of these compounds include both molar mass and structural effects Thus, answer choice C is the best answer

monoprotic acid to be 4.69 – 4.88 Answer choice A (4.8) lies in this range, the other choices do not

Alternatively, Figure 1 shows the pH at the half equivalence point of a weak acid to be about 4.8 Thus, answer choice A is the best answer

48. The first sentence of the passage states that the unknown “was a liquid at room temperature (20oC).” Table 1 shows that the melting point of crotonic acid is 71.6oC, which means it is a solid at room temperature (i.e., it melts 51.6oC above room temperature) Thus, answer choice C is the best answer

50. Conservation of linear momentum requires: mradon vradon=mhelium vhelium with helium identified

as the alpha particle The nuclear masses can be approximated by their mass numbers (222 and 4) Thus, the recoil speed of the radon is (4/222) * 1.5 x 107 m/s= 2.7 x 105 m/s Therefore, answer choice B is the best answer

51. The overall order of a reaction is the sum of the exponents of the concentrations in the rate law The exponent of [NO2] is 1 and that of [F2] is 1, and their sum is 1+1=2 Thus, the overall order is two or second order Thus, answer choice C is the best answer

The question asks for the enthalpy change (∆H) for the reverse reaction When the reaction is reversed, the sign of

∆H is changed from –to + Thus, the reverse reaction requires +185.0 kJ = Answer D

55. A stronger B field increases the magnetic force, Fm = q v B┴ The electric force must also increase to achieve equilibrium This implies a larger electric field in the artery and a larger voltage across the artery Thus, answer choice C is the best answer

56. Volume flow rate is the product of blood speed and artery cross-sectional area: (0.20 m/s)·( л /4) · (1.0 x 10-2 m)2 = 5л x 10-6 m3/s Therefore, answer choice B is the best answer

choice B is the best answer

58. A magnetic force acts on a moving charge in a direction that is perpendicular to both the velocity of the charge and the direction of the magnetic field This is a basic law of the interaction of electric currents and magnetic fields Thus, answer choice D is the best answer

59. The passage states that sulfuric acid reacts with Cu(s) to produce Cu+ and SO2 Thus, sulfuric acid is converted into sulfur dioxide, or H2SO4→SO2 The oxidation number of sulfur in H2SO4 can be found by assigning oxidation numbers of +1 for hydrogen and -2 for oxygen For the formula H2SO4 to be neutral, the sum of the oxidation numbers must be zero If x is the oxidation number of sulfur in H2SO4, then: 2(1) + 4(-2) + x=0, and x=+6 Likewise, for SO2: 2( - 2) + x=0, and x=+4 The change in oxidation number is from +6

to +4, which is answer choice B

60. The boiling point of HNO3 is given in the question as 86oC Because HNO3 must boil out of the flask and be trapped in the tube, the temperature of the flask must be above the boiling point of HNO3 (i.e., <86oC) and the temperature of the tube must be less than the boiling point of HNO3 (i.e, <86oC) Answer B meets these criteria; the other answers do not Thus, answer choice B is the best answer

61. The combustion of elemental sulfur involves a reaction between oxygen (O2) and sulfur (S) [Note: Though sulfur exists as S8 molecules, its reactions are normally written in terms of its empirical formula S.] Only Answer D shows such a reaction Thus, answer choice D is the best answer

62. The reaction involves the formation of gaseous SO3 from gaseous O2 and gaseous SO2

According to Le Châtelier's principle, any action that causes the reaction to shift toward the right will cause O2 and

SO2 to react and increase the yield of SO3 Of the four possible actions (answers A-D), the removal of SO3 as it forms will shift the reaction toward the right and is the most likely action to increase the yield of SO3 Thus, answer C is the best answer

In the conversion, hydrogen goes from an oxidation state of +1 in sulfuric acid to 0 (zero) in H2 Thus, the hydrogen in

H2SO4 is reduced (i.e., it undergoes an algebraic decrease in oxidation state) Fe(s) is the reducing agent (i.e., it causes the reduction) Thus, answer choice A is the best answer

65. The first ionization of sulfuric acid, H2SO4, is normally 100% in water However, under conditions of low water content, all of the H2SO4 cannot ionize Qualitatively, the only source of SO42- is HSO4- The Ka for the second ionization step of a parent acid is a few orders of magnitude smaller than that of the first step; therefore, SO4-2 must be the least abundant species, because it is only formed in the second ionization step Thus, answer choice A is the best answer

Quantitatively, the mass relationship in 100g of 98% H2SO4 is 98g H2SO4 and 2g H2O The molar mass of H2SO4 is

98 g/mol and of water is 18 g/mol Thus, in 100 g of 98% H2SO4 there is one mole of H2SO4 and 2/18 or 1/9 mole of

H2O In excess water, H2SO4 would ionize completely However, in this case (i.e., very low water content), only about 1/9 of a mole can react stoichiometrically with water to form H3O+ and HSO4- Of this 1/9 mol, only a small fraction of the HSO4- further ionizes to H3O+ and SO4-2, because HSO4-2 is a weak acid Therefore, SO4-2 is the chemical with the lowest concentration Thus, answer choice A is the best answer

66. The reflected radar signal has a frequency shift due to the Doppler effect Mercury must have been moving toward the Earth for the shift to be to a higher frequency Thus, answer choice A is the best answer

67. An equatorial bulge of the Sun would be caused by some process that is not the same in all directions

Of the four answers, only the Sun's rotation about an axis fulfills this condition The bulge is related to the balance between the centripetal force and the gravitational force Therefore, answer choice A is the best answer

68. The perihelion will have moved through an angle θ=Ω·t after a time t has elapsed The conversion of angles is given by the following An arcsecond is 1/60 of an arcminute An arcminute is 1/60 of a degree The time for 500 arcseconds per century to accumulate to θ=360 degrees is 360/(500/(60 x 60)) = 360 x 60 x (60/500) centuries Thus, answer choice C is the correct answer

hydrogen gas and produces ZnCl2(aq) Answer choice B is the best answer

73. Power is defined as the rate of doing work For the automobile, the power output is the amount of work done (overcoming friction) divided by the length of time in which the work was done Therefore, answer choice D is the best answer

74. The bonds labeled C and D in the figure are of equal length but shorter than bond B This is because two resonance structures can be drawn: in one resonance structure, bond C is a double bond, and in the secondresonance structure, bond D is double bond Double bonds (bond order = 2) are shorter than single bonds

76. In radioactive decay, the sum of the mass numbers A and atomic numbers Z, before and after decay, must balance The numbers for beryllium undergoing positron decay are: mass (7= 7 + 0) and atomic (4 = 3 + 1) The resulting nucleus is 73Li Thus, answer choice B is the best answer

77. Work is the product of force and distance The easiest way to calculate the work in this pulley problem

is to multiply the net force on the weight mg by the distance it is raised: 4 kg x 10 m/s2 x 5m = 200J

Therefore, answer choice D is the best answer

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