In an experiment to identify salts that could be used for Hot and cold packs, a

Question

In an experiment to identify salts that could be used for Hot and cold packs, a student found the following results when5.0 g of each salt was added to 25 mL of water in a coffee-cup calorimeter salt A-deltaT = -3.5 degree C salt B- delta T = +4.5 degreeC Salt C -deltaT = -6.5 degree C Salt D-delta T = +7.5 degree C Identify the salts that can be used as hotpacks. Salt A & Salt B Salt B & Salt D Salt A & Salt C All of them In an experiment to identify salts that could be used for Hot and cold packs, a student found the following results when5.0 g of each salt was added to 25 mL of water in a coffee-cup calorimeter salt A-deltaT = -3.5 degree C salt B- delta T = +4.5 degreeC Salt C -deltaT = -6.5 degree C Salt D-delta T = +7.5 degree C Calculate the enthalpy of solution of Salt A if the molar mass of Salt A 60.0 g/mol. Assume the density of water to be 1.00g/ml and the specific heat of the solution is 4.184 J/g.K -439 J -5.27 KJ +5.27 KJ +439 J

Explanation / Answer

1. Salts to be used as Hotpacks are,

Salt B and salt D

2. Enthalpy of salt A = -q = -mCpdT

= 25 g x 4.184 x -3.5 = -366.1 J

enthalpy in per mole of salt A = -366.1 x 60/5 = -4.39 kJ/mol

The answer should actually be,

-4.39 kJ instead of -439 J

[pl. note : a difference of decimal in the calculated value to the asnwer given]

3. The salts that dissolve in an exothermic process are,

Salt A and Salt C

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