Physics section test (5)

The energy content of the sample can be determined by measuring the change in temperature of the water with a simple thermometer.. However, before the heat or energy produced by the rea

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MCAT Section Tests

Dear Future Doctor,

The following Section Test and explanations should be used to practice and to assess your mastery of critical thinking in each of the section areas Topics are confluent and are not necessarily in any specific order or fixed proportion This is the level of integration in your preparation that collects what you have learned in the Kaplan classroom and synthesizes your knowledge with your critical thinking Simply completing the tests is inadequate; a solid understanding of your performance through your Score Reports and the explanations is necessary to diagnose your specific weaknesses and address them before Test Day

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Sincerely,

Albert Chen

Executive Director, Pre-Health Research and Development

Kaplan Test Prep

or mechanical without the written permission of Kaplan, Inc This book may not be duplicated,

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Physical Sciences

Test 3

Time: 38 Minutes

Number of Questions: 29

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PHYSICAL SCIENCES

DIRECTIONS: Most of the questions in the following Physical Sciences test are organized into groups, with

a descriptive passage preceding each group of questions Study the passage, then select the single best answer to each question in the group Some of the questions are not based on a descriptive passage;

you must also select the best answer to these questions If you are unsure of the best answer, eliminate the choices that you know are incorrect, then select an answer from the choices that remain

Indicate your selection by blackening the corresponding circle on your answer sheet A periodic table is provided below for your use with the questions

PERIODIC TABLE OF THE ELEMENTS

1

H

1.0

2

He

4.0

3

Li

6.9

4

Be

9.0

5

B

10.8

6

C

12.0

7

N

14.0

8

O

16.0

9

F

19.0

10

Ne

20.2

11

Na

23.0

12

Mg

24.3

13

Al

27.0

14

Si

28.1

15

P

31.0

16

S

32.1

17

Cl

35.5

18

Ar

39.9

19

K

39.1

20

Ca

40.1

21

Sc

45.0

22

Ti

47.9

23

V

50.9

24

Cr

52.0

25

Mn

54.9

26

Fe

55.8

27

Co

58.9

28

Ni

58.7

29

Cu

63.5

30

Zn

65.4

31

Ga

69.7

32

Ge

72.6

33

As

74.9

34

Se

79.0

35

Br

79.9

36

Kr

83.8

37

Rb

85.5

38

Sr

87.6

39

Y

88.9

40

Zr

91.2

41

Nb

92.9

42

Mo

95.9

43

Tc

(98)

44

Ru

101.1

45

Rh

102.9

46

Pd

106.4

47

Ag

107.9

48

Cd

112.4

49

In

114.8

50

Sn

118.7

51

Sb

121.8

52

Te

127.6

53

I

126.9

54

Xe

131.3

55

Cs

132.9

56

Ba

137.3

57

La *

138.9

72

Hf

178.5

73

Ta

180.9

74

W

183.9

75

Re

186.2

76

Os

190.2

77

Ir

192.2

78

Pt

195.1

79

Au

197.0

80

Hg

200.6

81

Tl

204.4

82

Pb

207.2

83

Bi

209.0

84

Po

(209)

85

At

(210)

86

Rn

(222)

87

Fr

(223)

88

Ra

226.0

89

Ac †

227.0

104

Rf

(261)

105

Ha

(262)

106

Unh

(263)

107

Uns

(262)

108

Uno

(265)

109

Une

(267)

*

58

Ce

140.1

59

Pr

140.9

60

Nd

144.2

61

Pm

(145)

62

Sm

150.4

63

Eu

152.0

64

Gd

157.3

65

Tb

158.9

66

Dy

162.5

67

Ho

164.9

68

Er

167.3

69

Tm

168.9

70

Yb

173.0

71

Lu

175.0

†

90

Th

232.0

91

Pa

(231)

92

U

238.0

93

Np

(237)

94

Pu

(244)

95

Am

(243)

96

Cm

(247)

97

Bk

(247)

98

Cf

(251)

99

Es

(252)

100

Fm

(257)

101

Md

(258)

102

No

(259)

103

Lr

(260)

GO ON TO THE NEXT PAGE.

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Physical Sciences 3

GO ON TO THE NEXT PAGE

Passage I (Questions 1–5)

The Kjeldahl method for determining the

percentage of nitrogen in a substance is an important

tool in industrial research It is commonly used to

determine the protein content of meats, grains,

fertilizers, drugs, and other biological substances

Because proteins from a particular source tend to

contain the same percent nitrogen, the percentage of

protein in the sample can be estimated quite accurately

by multiplying the percentage of nitrogen by a known

factor This factor is 6.25 for meats, 6.38 for dairy

products, and 5.70 for cereals

The sample to be analyzed is first decomposed in

hot, concentrated sulfuric acid (H2SO4), which

oxidizes carbon and hydrogen to CO2 and H2O

respectively Amine and amide nitrogens are

quantitatively converted to ammonium ion (NH4+)

The hot sulfuric acid decomposition, or digestion,

proceeds slowly, especially with substances that are

resistant to H2SO4 (e.g., heterocyclic compounds like

pyridine) Digestion times for these compounds can

often be decreased by adding a neutral salt, such as

potassium sulfate (K2SO4), to the digestion mixture

The digest is then cooled, and made basic with 50%

NaOH This process liberates ammonia:

NH4+ + OH–→ NH3(g) + H2O

Reaction 1 This gaseous ammonia is then distilled into a

flask containing an excess of boric acid, which

converts the ammonia back to the ion as follows:

H3BO3 + NH3? NH4+ H2BO3–

Reaction 2 Reaction 2 produces an acidic solution

containing the borate ion The borate ion is then

titrated with standardized HCl to find the percent

nitrogen

1 A technician is analyzing 0.1 g of beef using the

Kjeldahl procedure The final titration of the

borate requires 5.5 mL of 0.01 M HCl Which of

the following represents the percentage of protein

in the sample?

A 0 01× 0 0055× 14

0 1 × 100

B 0 01× 0 0055× 2 × 14

C 0 01× 0 0055× 14

0 1 × 100 × 6 25

D 0 01× 0 055 × 14

0 1 × 100 × 6 25

2 According to the Brønsted-Lowry acid-base

theory, which of the following pairs shows the conjugate acid of NaOH and the conjugate base

H3BO3, respectively?

A H2O and NH3

B NH3 and NH4+

C H2SO4 and H2BO3

D H2O and H2BO3

3 Which of the following acid-base indicators

would be used to find the endpoint in the titration

of the H2BO3 produced in Reaction 2 with standardized HCl?

A Bromocresol green (pH of transition = 3.8 to

5.4)

B Cresol purple (pH of transition = 7.6 to 9.2)

C Phenolphthalein (pH of transition = 8.3 to

10.0)

D Phenol red (pH of transition = 6.8 to 7.4)

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4 Which of the following compounds is least likely

to need K2SO4 added to its digestion mixture?

A A guanine base

B A cyclic alkene

C A furan compound

D A pyrrole derivative

5 H3BO3 can be classified as:

A a polyprotic acid

B a polyprotic organic acid

C the conjugate base of H2BO3

D a reducing agent

Passage II (Questions 6–10)

Food is digested by the body in a series of steps, and the body uses the energy released at each step for body functions This is the process of metabolism The overall energy released by the metabolic process equals the energy released in the equivalent combustion process Thus, by measuring the amount

of energy released during combustion, we can find the energy that a particular food provides to the body

A constant-volume calorimeter, shown in Figure

1, measures the energy content of a substance The bomb, which holds the sample to be measured, is a container filled with oxygen gas at a given pressure The bomb itself resides in a thermally isolated container, which holds 2000 g of water The sample is ignited electrically, and its combustion produces heat,

which the water and bomb absorb The energy content

of the sample can be determined by measuring the change in temperature of the water with a simple thermometer

However, before the heat or energy produced by the reaction can be calculated, it is necessary to calibrate the calorimeter: that is, the heat capacity of

the bomb must be determined The heat capacity of the

bomb is the product of the specific heat and the mass

of the bomb (Note: The specific heat of water is

4,190 J/kg • K.)

Figure 1

6 A heater is placed in the calorimeter to calibrate

it Which of the following physical quantities need to be determined?

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A The change in temperature only

B The change in temperature and the power of

the heater

C The power of the heater and the time the

heater operated

D The change in temperature, the power of the

heater, and the total time it operated

7 Why must the container be thermally isolated ?

A So all the heat released by the sample will be

absorbed by the water

B So all the heat released by the sample will be

absorbed by the bomb and the water

C So that the system will always be in thermal

equilibrium

D So that the system will not conduct

electricity

8 If the bomb is not sufficiently thermally isolated

and lets heat escape, how would it affect the

calculated energy content of the food being

measured?

A The calculated value would be less than the

actual value because the enthalpy change of

combustion is maximized under adiabatic

conditions

B The calculated value would be less than the

actual value because the observed

temperature change of the water would be

lower

C The calculated value would be higher than

the actual value because the reaction would

release more heat to compensate for the heat

loss in accordance with le Châtelier’s

principle

D The calculated value would be higher than

the actual value because the heat capacity of

the calorimeter would decrease

9 A sample of 2-methyl-naphthalene is submerged

in a bomb with a heat capacity of 1,620 J/°C

which is submerged in a calorimeter containing 2

kg of water If the temperature of the water

increases by 2°C when the sample is ignited, what

is the heat released in joules?

A (1620 + 2) ∞ 2

B (1620 + 2 ∞ 4190) ∞ 275

C (1620 + 2 ∞ 4190) ∞ 2

D It cannot be determined unless the mass of

the calorimeter is known

10 What happens to the entropy of the calorimeter

system after the combustion of a sample?

A It increases

B It decreases

C It remains the same

D It increases and then decreases

Passage III (Questions 11–16)

Titration is a common procedure used in quantitative analysis Two reagents that are often used for this purpose are potassium iodide and sodium thiosulfate Iodide is used to standardize, or establish

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the molarity of, a thiosulfate solution First, an

aqueous solution of iodine is prepared by adding an

excess of potassium iodide to a known volume of an

acidic solution of potassium iodate

IO3 + 5 I– + 6 H+? 3 I2 + 3 H2O

Reaction 1 The iodine combines with excess iodide to form

triiodide, by the following reaction:

I2 + I–

I3 Keq = 7.1 ∞ 102 Reaction 2

Triiodide solutions are commonly referred to as

iodine solutions since this terminology adequately

explains the stoichiometry of this reagent (I2 + 2e–?

2I–)

The iodine solution resulting from Reaction 1 is

titrated with the thiosulfate solution that is to be

standardized The two half-reactions that occur are:

E°(V)

2 S2O32–? S4O62– + 2 e– –0.09

Reaction 3

I2+ 2 e–? 2 I– 0.54

Reaction 4

The endpoint of this titration is determined by

adding starch, a common iodine indicator, and

watching for disappearance of the deep blue

starch/iodine complex The molarity of thiosulfate is

then determined from the amount of iodate consumed

in Reaction 1

An application of this technique is the use of a

standardized thiosulfate solution, together with

potassium iodide, to determine the percentage of

copper in brass A weighed sample of brass is

dissolved in nitric acid, and an excess of KI is added

to the acidified solution This produces the following

reaction:

2 Cu2+ + 4 I–? 2 CuI(s) + I2

Reaction 5 The liberated iodine is then titrated with

thiosulfate to the endpoint

11 2 g of KI (MW 166.0) are added to 50 mL of a

0.010 M KIO3 solution This solution is titrated

with 32.60 mL of an unstandardized sodium

thiosulfate solution (MW 158.10) Which

calculation indicates the molarity of the thiosulfate solution?

A ( 0 01)(0 05)(3 )

32 60

B ( 0 01)(0 05)(6 ) ( 214 0 )(0 03260 )

C ( 0 01)(0 05)(6 ) ( 0 03260 )

D ( 2 )(0 01)(0 05)(6 ) ( 166 0 )(0 03260 )

12 In the reaction between iodine and thiosulfate,

which species are reducing agents?

A I2 and S4O62–

B S4O62– and S2O32–

C S2O32– and I2

D S2O32– only

13 What is the standard potential for the redox

reaction between thiosulfate and molecular iodine?

A –0.63 V

B –0.45 V

C 0.45 V

D 0.63 V

14 The reduction of copper (II) to copper (I) has a

standard half-cell potential of only 0.15 V Considering this fact, how is it possible for copper to be reduced by iodide?

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I The reaction is thermodynamically

favored, and therefore is spontaneous

II The reaction is forced to completion by

an excess of iodide and by the formation

of copper (I) iodide

III The oxidation of iodide is favored under

acidic conditions, as shown in Equation

1

A I only

B II only

C I and II only

D II and III only

15 The titration described in the passage determined

that there were 0.01 moles of copper in 1.90 g of

brass What is the percentage of copper in this

brass sample?

A 1%

B 3%

C 33%

D 66%

16 If sodium hydroxide were added to Reaction 1,

how would the equilibrium constant of Reaction

2 change?

A It would increase because iodide would be

removed from the solution as NaI salt

B It would increase because the excess water

produced would lower the concentrations of

iodine and iodide

C It would remain the same because Reaction 1

and Reaction 2 are unrelated

D It would remain the same because the

equilibrium constant for a reaction is the

same for all concentrations of reactants and

products at the same temperate

Questions 17 through 21 are

NOT based on a descriptive

passage

17 A thin converging lens of focal length 100 mm is

used as a magnifying glass If the object viewed is

80 mm from the lens, how far from the lens will

the image be?

A 40 mm

B 44 mm

C 400 mm

D At infinity

18 Which factors would you need to determine the

density of oxygen in a vessel containing a mixture

of gases, using the formula PV = nRT?

A The partial pressure of oxygen and the

number of moles of oxygen in the container

B The partial pressure of oxygen and the total

number of moles of gas in the container

C The total pressure of gas in the container and

the number of moles of oxygen in the container

D The total pressure of gas in the container and

the total number of moles of gas in the container

19 A train is moving at 30 m/s The conductor

sounds the horn which has a frequency of 100

Hz What is the frequency that a passenger on the train hears?

A 85 Hz

B 100 Hz

C 110 Hz

D Cannot be determined

20 If 230 g of ethanol (C2H5OH) are added to 180 g

of water, by how much does the vapor pressure of the water change?

A It decreases by 33%

B It decreases by 50%

C It decreases by 56%

D It decreases by 67%

21 The pressure in a non-compressible liquid:

A increases with depth

B decreases with depth

C depends upon the shape of the container

D depends upon the total volume of the fluid

Passage IV (Questions 22–29)

Circular particle accelerators, such as the cyclotron, have been used for over 50 years to gain a better understanding of the nature of elementary particles The cyclotron is depicted in a top view in Figure 1 and in a side view in Figure 2 This accelerator is composed of two hollow, metal,

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shaped containers, called dees They are connected to

an alternating voltage supply Above and below the

dees are electromagnets that create a uniform

magnetic field

Initially, charged particles are at the center of the

cyclotron accelerator, which is point S in Figure 1

Originally, one of the dees is at a positive potential,

and the other is at a negative potential In the case of a

positively charged particle, the particle will be

accelerated towards the dee with a negative potential

and will enter it Inside the dee, the electric field is

zero, due to the shielding of the dee However, a

magnetic force is present, which causes the particle to

execute uniform circular motion By the time the

particle comes to the edge of the dee, the alternating

voltage has changed so that the particle now faces the

negative dee, and is again accelerated by the potential

difference

The frequency of the particle’s circular motion

can be related to the magnetic field by the equation:

qB = 2? mv where q is the charge, B is the magnetic field strength,

m is the mass of the charge and v is the frequency of

the circular motion Note that the frequency of the

particle does not depend on its speed; faster particles

will travel in larger circles The frequency of the

voltage supply is therefore set equal to the frequency

of the particles, and both quantities remain constant

A particular cyclotron is used to accelerate

protons It has a radius of 0.5 m, an oscillator

frequency of 10 MHz and a maximum voltage of 100

kV (Note: 1 eV = 1.6 ∞ 10–l9 J Also, the

fundamental unit of charge, e, equals 1.6 ∞ 10–l9 C

and the mass of a proton is 1.6 ∞ 10–27 kg.)

Figure 1

Figure 2

22 Which of the following diagrams correctly

depicts the directions of the acceleration and velocity vectors of a charged particle traveling in

a cyclotron dee?

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23 If a proton travels in a clockwise direction in the

cyclotron, as shown in Figure 1, what is the

direction of the magnetic field created by the

electromagnets?

A Out of the page

B Into the page

C Towards the top of the page

D Towards the bottom of the page

24 Which of the following correctly gives the value

of the energy of a proton inside the dee in terms

of the mass, m, the charge, q, the magnetic field

strength, B, and the radius of the dee, r?

A. qBr

m 2

B q 2 B 2 r 2

2 m

C qBr

2 m

D q 2 B 2 r 2

m 2

25 Which of the following adequately describes

when the particles are accelerating?

A Only inside the dees because only there does

the particles’ speed changes

B Only between the dees because only there

does the particles’ speed changes

C Throughout the entire cyclotron because the

particles are changing speed between the dees

and changing direction within the dees

D Throughout the entire cyclotron because the

particles are changing direction between the

dees and changing speed within the dees

26 Which of the following equations correctly

describes the voltage at a given time, t, for the

cyclotron? (Note: Use units of volts and

seconds.)

A (7 ∞ 104) sin ((2? ∞ 107)t)

B (105) sin (10–7 t)

C (105) sin (107 t)

D (105) sin ((2? ∞ 107)t)

27 What is the ratio of the period of a proton 0.5 m

from the source to one 0.25 m from the source?

A 1:1

B 1:2

C 2:1

D 4:1

28 A proton in a cyclotron moving with an energy of

10 MeV and speed of 4.4 ∞ 107 m/s strikes a stationary hydrogen ion target After the collision the target moves with a speed of 3.5 ∞ 107 m/s (6.4 MeV) and the proton moves with an energy

of 0.42 MeV Which of the following statements about this collision is true? (Assume that the particles move along the same path after the collision.)

A The collision is completely inelastic

B The collision is completely elastic

C The final speed of the incident proton is 0.9

∞ 107 m/s

D Momentum is not conserved

29 If the magnetic field in the accelerator increases,

what factor must be changed to keep the final velocity of the protons constant?

A The oscillator frequency must be decreased

B The radius of the dees must be decreased

C The voltage must be decreased

D The radius of the dees must be increased

END OF TEST

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