Hot packs can be used to comfort sore muscles and similar conditions. A hot pack is activated by breaking a barrier on the inside of the pack, allowing the chemicals inside to mix. The process that occurs is exothermic, meaning it releases heat and causes the pack to feel hot. A group of students wanting to create their own hot pack made the design shown below.

Question

The group of students then did an experiment using four different solutes to see which one would be best in their hot pack. To determine which solute would be best, the students mixed 20 g of each solute into separate containers that each held 50 mL of 24°C water. The students then recorded the temperature changes in each container. The data table below shows the maximum and minimum temperature they obtained for each solute, as well as the temperature difference.

Maximum Temperature (°C) Minimum Temperature (°C) Temperature Difference (°C)
Ammonium chloride (NH4Cl) 24 1 23
Calcium chloride (CaCl2) 60 24 36
Sodium acetate (CH3COONa) 55 24 31
Sodium chloride (NaCl) 24 22 2

According to the students' data, which solute should they use in their hot pack?
A.
ammonium chloride
B.
sodium acetate
C.
sodium chloride
D.
calcium chloride

Answer 1

To determine which solute would be best for the hot pack, we need to look at the temperature differences recorded during the experiment, as this indicates how much heat was released by the solute when it was mixed with water. The larger the temperature difference, the more effective the solute is in generating heat.

From the data given:

• Ammonium chloride (NH4Cl): Temperature Difference = 23°C
• Calcium chloride (CaCl2): Temperature Difference = 36°C
• Sodium acetate (CH3COONa): Temperature Difference = 31°C
• Sodium chloride (NaCl): Temperature Difference = 2°C

The solute that produced the largest temperature difference was calcium chloride (CaCl2) with a temperature difference of 36°C.

Thus, the best solute to use for their hot pack is:

D. calcium chloride