Introduction: The purpose of this lab was to determine which was the best and least toxic de-icer. In order to find this out, experimenting had to be done. Water, along with three different de-icers were measured to figure out their boiling point. Finding the boiling point was found because its easier to find than the freezing point due to the circumstances in the classroom. These freezing point depressions and boiling point elevations are known as colligative properties of a solution. They directly depend on the concentration of the solution, the number of dissolved solute particles in the solvent. It is also known that the highest boiling point also has the lowest freezing point. As stated before, the purpose of this lab was to find the de-icer that was the most efficient and the least toxic and damaging to earth. This is an example of green chemistry. Green chemistry is designing chemical products and processes that reduce or eliminate the use and the generation of hazardous substances. After the boiling point of the substances were calculated, the toxicity of them were tested. It was important that the lethal dose of the substances were known. A lethal dose (LD50) refers to the amount of substance that kills 50% of a test sample. It is expressed in mg/kg or milligrams of substance per kilogram of body weight. The hypothesis that was created at the start of these experiments was that the 1% de-icer solution would be the best choice; for it was efficient and the not as toxic.
Procedure: Colligative Properties/Boiling Point:
Record the molarity of the 1%, 5% and 10% de-icer solutions
Add 100mL of the solution to a 250 mL beaker
Set the beaker on a hot plate, turn the hot plate to 7
Place a watch glass over the beaker, concave side down
Wait for the solution to come to a boil.
Once it comes to a hard boil, take a measurement of the temperature every 30 seconds until it has reached 4 readings of the same temperature.
The last temperature measured is the boiling point of your solution.
Calculate the change in boiling point by subtracting the boiling point of water from the boiling point of your solution. Toxicity: (not able to perform due to the fact the daphnia died before they were tested) Record the identity and concentration of your de-icer Fill the petri dish with the salt solution Receive the daphnia Add 6-10 daphnia to the petri dish and start the timers Carefully watch the daphnia. Record the time when 50% of the daphnia in each petri dish have died Record the time when 100% of the daphnia have died
The purpose of boiling water with no de-icer present in the colligative properties lab was to be able to find out the boiling point of water. Once that was found, it was then possible to find the change in the boiling points of the solutions with de-icers present by subtracting their boiling point with the boiling point of the plain water. For example, the 1% de-icer solution had a boiling point of 107 degrees. It was then subtracted by the boiling point of plain water. 107-104=3. So, 3 was the change in boiling point.
It was important to have more than one group use each de-icer because it could further prove that the information was correct. It is a controlled variable.A controlled variable is one that is not allowed to change unpredictably during an experiment. They are ideally expected to remain the same, so they are also called constant variables. It also, because no human is perfect, can prove that no mistakes were made. For example, the if more than one student received the same information, it was more likely for them to be right than them all to be wrong.
The amount of time the daphnia survive int he de-icer told us how toxic each substance was. The shorter amount of time it took for the daphnia to die, the more toxic the substance was. Whereas the