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