AccelePrep for the ACT Test 2nd Edition Student Text

286 • P OWER U P ! T HE E XCLUSIVE C AMBRIDGE S AMPLE E XAM

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PRACTICE TEST 18B

SECTION 4: SCIENCE TEST 35 Minutes—40 Items

DIRECTIONS: Each passage below is followed by several items. After reading a passage, choose the best answer for each item. Fill in the corresponding oval on your bubble sheet. You may refer to the passage as often as necessary. You are NOT permitted the use of a calculator on this test. Answers are on page 313.

PASSAGE I Alkanes are open-chain organic compounds that have the general chemical formula C n H 2 n +2 . For example, propane has the following structural formula: CH 3 — CH 2 — CH 3 For propane, n = 3 (the number of carbon atoms), and 2(3) + 2 = 8 (the number of hydrogen atoms). The series of linked carbon atoms is called the carbon backbone of the compound, and the number of carbon atoms in the backbone gives the compounds their different names. Alkanes that differ by one carbon atom differ in molecular mass by 14u (one carbon atom of mass 12u and two hydrogen atoms of mass 1u each).

Physical Properties of Straight-Chain Alkanes

Molecular Mass (atomic mass unit, u)

Density (g/cm 3 at 290°C) 0.466 0.572 0.585 0.601 0.626 0.660 0.684

Name methane 1 ethane 2 propane 3 butane 4 0 pentane 5 36 hexane 6 69 heptane 7 98 octane 8 126 nonane 9 151 decane 10 174 # of Carbons 162 89 42

Boiling Point (°C)

Melting Point (°C)

Flash Point (°C)

16 30 44 58 72 86 100

183

183

818

138

130

49

95

114 13 0.703 128 31 0.718 142 46 0.730

91

57

54

30

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