EFFECTIVENESS OF AMMONIUM NITRATE VS. UREA FOR USE IN INSTANT COLD PACKS

The purpose of this experiment was to determine which chemical, ammonium nitrate or urea, in water produces the lowest temperature for use as a cold compress. Research led to the hypothesis: ammonium nitrate will produce lower temperatures in solution than urea. The hypothesis was tested by evaluating minimum water temperatures produced. Eighty grams of ammonium nitrate or urea was poured into a styrofoam cup containing 100 ml of distilled water at 20°C. The infrared thermometer was immediately started, recording temperatures at 1 s intervals. The solution was constantly stirred, and temperature recording continued until the minimum temperature stabilized. The final minimum temperatures (°C) were recorded along with the times (seconds) to produce them. Ten trials were performed for each type of chemical for a total of 20 trials. Mean minimum temperatures, times, and standard deviations were calculated. The mean minimum solution temperature was -12.4°C (σ=0.5°C) for ammonium nitrate and -4.1°C (σ=0.3°C) for urea. This result supports the hypothesis. The mean time to produce the minimum temperature was 180s (σ=18s) for ammonium nitrate
and 228s (σ=26s) for urea. Therefore, all of the data shows that ammonium nitrate produces lower mean minimum temperatures, and reaches them more quickly, demonstrating it is a more effective chemical for use in instant cold packs.