Cold packs can be used to treat sprained ankles and similar injuries. A cold pack is activated by breaking a barrier within the the pack, allowing the chemicals inside to mix. The process that occurs is endothermic, meaning it absorbs heat and leaves the pack feeling cold, as shown in the diagram below.

Question

A group of students wants to create their own cold pack, so they did an experiment using four different solutes to see which one would be best. 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 temperatures 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 cold pack?
A.
sodium chloride
B.
calcium chloride
C.
sodium acetate
D.
ammonium chloride

Answer 1

To determine which solute would be best for their cold pack, the students should consider the temperature difference observed with each solute, as a greater temperature decrease indicates a more effective endothermic reaction that absorbs more heat from the surroundings.

From the data provided:

• 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 when mixed with water is calcium chloride (CaCl2), with a temperature difference of 36°C. This suggests that it has the most significant cooling effect and would be the best choice for their cold pack.

Therefore, the answer is:

B. calcium chloride