Salt Mass(g) Initial Temperature Final Temperature Heat of Solution Ammonium Chl

Question

Salt

Mass(g)

Initial Temperature

Final Temperature

Heat of Solution

Ammonium Chloride

5.0098

23.6C

20.3C

-1449J

Calcium Chloride

5.0045

23.3C

29.7C

2809J

Lithium Chloride

5.0650

23.6C

32.9C

4084J

Sodium Acetate

5.0009

23.5C

25.6C

922J

Sodium Carbonate

5.0804

23.5C

24.9C

615J

Sodium Chloride

5.0399

23.3C

22.3C

-439

Extrapolating from the information collected, predict which solid(s) could be used to design a hand warmer meeting the following requirements:

a. The hand warmer must contain 10 grams of an ionic solid and 40 ml of water

b. Activating the hand warmer must increase the temperature of the resulting solution by at least 20 degrees C

c. The solid chosen should be nontoxic, safe for the environmet, and economical

Name Molecular Formula Molar Mass(g/mol) Price($/kg) Ammonium Chloride NH4Cl 53.49 21.90 Calcium Chloride CaCl2 110.98 10.80 Lithium Chloride LiCl 42.39 68.30 Sodium Acetate C2H3NaO2 82.03 27.30 Sodium Carbonate Na2CO3 105.99 5.95 Sodium Chloride NaCl 58.44 4.25

Explanation / Answer

q = m cg t, or

t = q / m cg

For all the cases,

msolid = 10 g, mwater = 40 ml x 1 g / mL (density of water) = 40 g, m = msolid + mwater = 50g

cg = specific heat capacity of water = 4.18 JoC-1g-1

Therefore t = q / (50 * 4.18) = q / 209

For Calcium Chloride,

q = (2809 J / 5.0045 g) x 10 g = 5612.95 J

t = 5612.95 / 209 = 26.86 C

For Lithium Chloride,

q = (4084 J / 5.0650 g) x 10 g = 8063.18 J

t= 8063.18 / 209 = 38.58 C

For all the other salts t < 20 C. (Do similar calculation as shown above).

Lithium chloride is known to be toxic: in humans, 5 g of LiCl can result in fatal poisoning. Calcium chloride is also cheaper than lithium chloride. Therefore calcium chloride is the most suitable salt.

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