August 2015 Chemistry Regents #66-68

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Questions 51-54 Questions 55-57 Questions 58-59 Questions 60-61 Questions 62-65 Questions 66-68 Questions 69-72 Questions 73-74  Questions 75-76  Questions 77-78  Questions 79-80  Questions 81-82  Questions 83-85

 

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Questions 66-68

 

 

Base your answers to questions 66 through 69 on the information below and on your knowledge of chemistry.

The two naturally occurring isotopes of antimony are Sb-121 and Sb-123. The table below shows the atomic mass and percent natural abundance for these isotopes.

Antimony and sulfur are both found in the mineral stibnite, Sb2S3. To obtain antimony, stibnite is roasted (heated in air), producing oxides of antimony and sulfur. The unbalanced equation below represents one of the reactions that occurs during the roasting.

Sb2S3(s) + O2(g) → Sb2O3(s) +  SO2(g)

66 Determine the percent composition by mass of antimony in stibnite (gram-formula mass = 340. g/mol). [1]

Answer-->71.6%

(Work not needed)  ((2*121.8)/340.)*100%

67 In the space in your answer booklet, show a correct numerical setup for calculating the atomic mass of antimony. [1]

Answer-->(120.90*57) + (122.90*43)/100

or           (120.90*0.57) + (122.90*0.443)

68 Complete the balancing of the equation in your answer booklet for the roasting of stibnite, using the smallest whole-number coefficients. [1]

Answer-->

2Sb2S3(s) + 9O2(g) → 2Sb2O3(s) +  6SO2(g)

on to Questions 69-72

 

Questions 1-5 Questions 6-10 Questions 11-15 Questions 16-20 Questions 21-25 Questions 26-30 Questions 31-35 Questions 36-40 Questions 41-45 Questions 46-50

Questions 51-54 Questions 55-57 Questions 58-59 Questions 60-61 Questions 62-65 Questions 66-68 Questions 69-72 Questions 73-74  Questions 75-76  Questions 77-78  Questions 79-80  Questions 81-82  Questions 83-85

 

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