3. Cold Packs contain solid Ammoniumnitrate that is physically separated fromsur

Question

3.

Cold Packs contain solid Ammoniumnitrate that is physically separated fromsurrounding water. Firm pressure on the outer bag ruptures thematerial encapsulating ammonium nitate. As the nitrate dissolves,the solution becomes colder. This solution process is characterizedby three steps:

1. The separation of solvent molecules - positive H
2. The separation of solute molecules - positive H
3. The formation of solute / solvent interactions - negative H

Because the third step's magnitude is less than the sum of thefirst two steps, the overall H ispositive.

A typical Cold Pack contains 40.0 g ammonium nitrate surrounded by100.0 g water. What is the Molarity of the liquid in a usedCold Pack (density = 1.155 g/mL)?

Explanation / Answer

         Atypical Cold Pack contains 40.0 g ammonium nitrate surrounded by100.0 g water.          Density =1.155 g/mL         Volume of Water =Mass/Density                                    =100.0 g / 1.155g/mL                                   = 86.6 mL        Number of moles ofAmmonium Nitrate = mass /Molar mass                                                                     =40.0 g /80.043 g/mol                                                                     =0.499 moles       Molarity of the solution is M=number of moles / Volume (mL)                                                    =0.499 moles/ 0.0866 L                                                     = 5.77 M       Molarity of the solution is M=number of moles / Volume (mL)                                                    =0.499 moles/ 0.0866 L                                                     = 5.77 M

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