January 2006 Chemistry Regents #31-40

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Questions 1-10 Questions 11-20 Questions 21-30 Questions 31-40 Questions 41-50

 

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Answer Explanations
31 Which electron configuration represents the electrons in an atom of chlorine in an excited state?
(1) 2-7-7      (3) 2-8-7
(2) 2-7-8      (4) 2-8-8
2 17 electrons and one is promoted
1 physical change is a change in intermolecular distances
33 What is the percent composition by mass of nitrogen in NH4NO3 (gram-formula mass = 80.0 grams/mole)?
(1) 17.5%     (3) 52.5%
(2) 35.0%     (4) 60.0%
2 (2N x 14 / 80) x 100%
34 The atomic mass of element A is 63.6 atomic mass units. The only naturally occurring isotopes of element A are A-63 and A-65. The percent abundances in a naturally occurring sample of element A are closest to
(1) 31% A-63 and 69% A-65
(2) 50% A-63 and 50% A-65
(3) 69% A-63 and 31% A-65
(4) 100% A-63 and 0% A-65
3 mostly 63 because the atomic mass is closest to that number. More than 50%.
35 Elements Q, X, and Z are in the same group on the Periodic Table and are listed in order of increasing atomic number. The melting point of element Q is 219C and the melting point of element Z is 7C. Which temperature is closest to the melting point of element X?
(1) 7C       (3) 219C
(2) 101C   (4) 226C
2 between the -7 and -219
36 Given the balanced equation:
2C + 3H2==> C2H6
What is the total number of moles of C that must completely react to produce 2.0 moles of C2H6?
(1) 1.0 mol     (3) 3.0 mol
(2) 2.0 mol     (4) 4.0 mol
4 2/1 C2H = x/ 2C

x=4

37 Given the balanced equation:
2KClO3==> 2KCl + 3O2
Which type of reaction is represented by this equation?
(1) synthesis
(2) decomposition
(3) single replacement
(4) double replacement
2 AB==> A + B

decomposition

38 A solid substance was tested in the laboratory.
The test results are listed below.
dissolves in water
is an electrolyte
melts at a high temperature
Based on these results, the solid substance could be
(1) Cu               (3) C
(2) CuBr2          (4) C6H12O6
2 properties of an Ionic compound
39 If 0.025 gram of Pb(NO3)2 is dissolved in 100. grams of H2O, what is the concentration of the resulting solution, in parts per million?
(1) 2.5 104 ppm    (3) 250 ppm
(2) 2.5 ppm                 (4) 4.0 103 ppm
3 Table T ppm, plug in
40 Given the balanced equation:
4Fe(s) + 3O2(g) ==>2Fe2O3(s) + 1640 kJ
Which phrase best describes this reaction?
(1) endothermic with DH = +1640 kJ
(2) endothermic with DH = -1640 kJ
(3) exothermic with DH = +1640 kJ
(4) exothermic with DH = -1640 kJ
4 exothermic, DH = -

Table I, on the way bottom

Questions 1-10 Questions 11-20 Questions 21-30 Questions 31-40 Questions 41-50

 
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