June 2012 Chemistry Regents #66-68

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Question 51 Questions 52-55 Questions 56-59 Questions 60-62 Questions 63-65 Questions 66-68 Questions 69-71 Questions 72-75  Questions 76-78  Questions 79-81  Questions 82-85

 

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Base your answers to questions 66 through 68  on the information below.

 

John Dalton. an early scientist, sketched the structure of compounds using his own symbols for the elements known at the time. Dalton's symbols for four elements and his drawing of potassium aluminum sulfate are represented by the diagram below.

Today, it is known that the chemical formula for potassium aluminum sulfate is KAl(SO4)212H2O. It is a hydrated compound because water molecules are included within its crystal structure. There are 12 moles of H2O for every 1 mole of  KAl(SO4)2. The compound contains two different positive ions. The gram-formula mass of KAl(SO4)212H2O is 474 grams per mole.

66 Identify one positive ion in the hydrated compound. Your response must include both the chemical symbol and charge of the ion. [1]

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Kor  Al3+

67 Describe, in terms of composition, one way in which Dalton's perception of potassium aluminum sulfate differs from what is known today about the compound. [1]

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No hydrogen in the drawing  or

formula has 2 sulfurs but he drew 5  or

drawing has more Al than the formula or

there is no water...plus some more

68 Show a numerical setup for calculating the percent composition by mass of water in

KAl(SO4)212H2O. [1]

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(12 (18)/474)   x 100%   or

(216/474)  x100% 

on to Questions 69-71

 

 

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

Question 51 Questions 52-55 Questions 56-59 Questions 60-62 Questions 63-65 Questions 66-68 Questions 69-71 Questions 72-75  Questions 76-78  Questions 79-81  Questions 82-85

 
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