Select each correct answer. More than one answer may be correct.

Question

Rodrigo is using the design process to make a device that will cool a drink without ice or electricity. His first prototype was simply an airtight, watertight pouch containing 40 g of ammonium chloride (NH4Cl). He added 100 mL of water to the ammonium chloride, sealed the pouch tightly, and then wrapped the pouch around a small bottle of water. He tested his prototype by measuring the temperature of the bottle of water over time.

Next, Rodrigo performed the same test with different amounts and different concentrations of the ammonium chloride solution. For each set of measurements, he found the lowest temperature reached by the bottle of water and calculated the total temperature change. The table below summarizes his results.

Maximum Cooling Achieved
trial 1 2 3 4 5 6 7
grams of NH4Cl 30 40 50 50 60 70 80
amount (mL) of
water added 100 100 100 150 150 200 200
greatest
temperature
change (–°C) 3.6 4.3 4.3 4.8 5.2 5.6 5.8
Finally, Rodrigo held the amount and concentration of the solution constant while trying different amounts of insulation.

Maximum Cooling Achieved
trial 8 9 10 11
insulation used: none towel blanket polystyrene foam
greatest
temperature
change (–°C) 5.8 8.8 9.3 9.6
Rodrigo wants to find more ways to improve his latest design. Which of the following should he try?

a more concentrated solution
a less concentrated solution
better insulation
less insulation
a greater amount of solution
a lesser amount of solution

Answer 1

Based on the data provided from Rodrigo's experiments, the following options could potentially improve his cooling device:

1. a more concentrated solution - Higher concentration could potentially enhance the cooling effect as there would be more solute to dissolve in the water, which could lead to a larger temperature change.

2. better insulation - The results show that with better insulation (moving from none to towel to blanket to polystyrene foam), the temperature change increased. This indicates that improving insulation further could lead to better cooling efficiency.

3. a greater amount of solution - Increasing the amount of NH4Cl, as seen in the trials (from 30 g to 80 g), resulted in greater temperature changes. Thus, using a greater amount of solution could also be beneficial.

The following options would likely not improve performance based on the results and descriptions provided:

• a less concentrated solution - This would likely decrease the cooling effect, based on the observation that higher concentrations lead to greater temperature changes.

• less insulation - This would likely allow for more heat transfer from the environment to the solution, thus reducing the cooling effect.

• a lesser amount of solution - This would reduce the potential for achieving a greater cooling effect, as seen in the trials indicating that more NH4Cl leads to more cooling.

In conclusion, the correct options for Rodrigo to try are:

• a more concentrated solution
• better insulation
• a greater amount of solution