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.
ammonium chloride
B.
sodium chloride
C.
calcium chloride
D.
sodium acetate

Answer 1

To determine which solute would be the best choice for the cold pack, we need to consider the temperature difference each solute produced when mixed with water. The greater the temperature difference, the more effective the cold pack will be at absorbing heat.

Based on the data provided, here's the temperature difference for each solute:

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

The solute with the largest temperature difference is calcium chloride (CaCl2) with a temperature difference of 36°C. This indicates that it absorbs the most heat from its surroundings, making it the best choice for a cold pack.

Therefore, the students should use:

C. calcium chloride