My PBl Project

Introduction:

My PBL project is centered around cold packs. More importantly where the heat goes in cold packs?

Materials:

• Styrofoam cups

• Water, distilled

• Graduated cylinder 100mL

• Gloves

• Goggles

• Instant cold packs

• Bowl

• Plastic spoons

• Newspaper

• Digital scale

• Digital thermometer

• Digital timer

Procedures:

• Label the Styrofoam cups with numbers 1 to 5.

• Add 100 mL of distilled water to each of the five cups.

• Cover the work surface with newspaper.

• Collect the ammonium nitrate from the instant cold pack, as follows:

• Put on your safety goggles and latex gloves.

• Shake the instant cold pack gently to move the water bag and crystals to the bottom.

• Cut the top of the bag off.

• Pour the ammonium nitrate crystals into the plastic bowl.

• Dispose of the water bag.

• Place one of the wax paper squares on the scale.

• Zero the scale.

• Use a plastic spoon to add 10.0 g of ammonium nitrate on the square/weigh boat.

• Record the starting temperature of the water in cup #1 in a data table in your lab notebook.

  • Point the digital thermometer at the water's surface and push the "on" button to get the temperature.

• Add 5.0 g of ammonium nitrate to the water in cup #1.

• Start the timer.

• Stir the contents with a plastic spoon.

• Record the temperature every 15 seconds (sec) until it stabilizes.

• You can record at longer intervals, such as 30 sec, if you choose.

• You might want a helper to write the times and temperatures down as you take the readings.

• Stir the contents of the cup gently between each reading.

• Remove the spoon when taking the temperature, as it may cause an error in the reading.

  • Stop taking readings when the temperature stops decreasing.

• Dispose of the ammonium nitrate solution down the sink.

• Repeat steps 6–10, with new and clean materials and equipment, adding the following amounts of ammonium nitrate. Note: You may need to divide the ammonium nitrate onto two or more pieces of wax paper/weigh boats if it will not all fit on one piece. Be sure to record the starting temperature, the intermediate temperatures, and the final temperature for each sample.

• 1. Cup #2: 10g

  2. Cup #3: 15g

  3. Cup #4: 20g

  4. Cup #5: 25g

• Repeat steps 1–12 two more times, so you have at least three trials. This ensures that your results are accurate and repeatable. Create a new data table for each trial. You can reuse the spoons and cups for the new trials, after rinsing them thoroughly with water.

• Dissolve any leftover ammonium nitrate in water and dispose of it in a sink.

Scientific Principles:

Exothermic-chemical reactions that produce heat.

Endothermic-reactions that are followed by the absorption of heat.

Ammonium Nitrate- a white crystalline solid used as a fertilizer and as a component of some explosives.

Ion-an atom or molecule with a net electric charge due to the loss or gain of one or more electrons

Heat energy-a form of energy that is transferred by a difference in temperature

Entropy-a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system.

Joules- unit for energy

Heat capacity- the number of heat units needed to raise the temperature of a body by one degree.

In cold packs there is a endothermic reaction that goes on. From the research I found out that cold pack becomes in a way ‘activated’ when the water and the ammonium nitrate in the cold pack mix. When this happens the cold packs starts to cool. This is because many cold packs contain ammonium nitrate a white crystalline solid which when dissolved with water spilt into positive ions and negative ions through this process the water cools and the cold pack in turn cools.