January 2007 Chemistry Regents #41-50

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

 

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AnswerExplanations
41 At room temperature, a mixture of sand and water can be separated by
(1) ionization       (3) filtration
(2) combustion     (4) sublimation		3filtering removes solids from liquids
42 Given the balanced equation representing a reaction at 101.3 kPa and 298 K:
N2(g) + 3H2(g) => 2NH3(g) + 91.8 kJ
Which statement is true about this reaction?
(1) It is exothermic and DH equals -91.8 kJ.
(2) It is exothermic and DH equals +91.8 kJ.
(3) It is endothermic and DH equals -91.8 kJ.
(4) It is endothermic and DH equals +91.8 kJ.		1it is exothermic so delta H is negative
43 Which balanced equation represents a phase equilibrium?
(1) H2(g) + I2(g)<==> 2HI(g)
(2) 2NO2(g) <==> N2O4(g)
(3) Cl2(g) <==> Cl2(l)
(4) 3O2(g)<==>  2O3(g)		3phase equilibrium is a phase change

NOT a REACTION

44 Given the system at equilibrium:
2POCl3(g) + energy <==> 2PCl3(g) + O2(g)
Which changes occur when O2(g) is added tothis system?
(1) The equilibrium shifts to the right and the concentration of PCl3(g) increases.
(2) The equilibrium shifts to the right and the concentration of PCl3(g) decreases.
(3) The equilibrium shifts to the left and the concentration of PCl3(g) increases.
(4) The equilibrium shifts to the left and the concentration of PCl3(g) decreases.		4adding a PRODUCT shift the equilibrium to the left

the reactants increase in concentration and the products decrease

45 What is the oxidation number of chromium in the chromate ion, CrO42–?
(1) +6   (3) +3
(2) +2   (4) +8		1each oxygen is 2-  (4 x2-)= -8

it adds up to -2    =-8 +X

46 Given the balanced equation representing a reaction:
H2SO4(aq) + 2KOH(aq) =>K2SO4(aq) + 2H2O(l)
Which type of reaction is represented by this equation?
(1) decomposition      (3) single replacement
(2) neutralization          (4) synthesis		2acid and base= neutralization
47 In which 0.01 M solution is phenolphthalein pink?
(1) CH3OH(aq)    (3) CH3COOH(aq)
(2) Ca(OH)2(aq)   (4) HNO3(aq)		2bases are pink,  look for OH  or table L
48 As the pH of a solution is changed from 3 to 6, the concentration of hydronium ions
(1) increases by a factor of 3
(2) increases by a factor of 1000
(3) decreases by a factor of 3
(4) decreases by a factor of 1000		4for each pH change it is 10xs stronger, pH changes by 3 it is 1000x's

hydronium determines acidity so it decreases when pH increases

11/8 is 3 half lives

34.5/3 = 11.5minutes per half life

1find the missing masses

 look at table O for the particle

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