Effects of Salt on Freezing Point of Water

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Mr. Blank

4/9/02

Effects of Salts on the Freezing Point of Water

In this experiment, you will study the effect that several solutes have on the Freezing Point of water. When a solute is dissolved in a liquid, the temperature at which that liquid freezes decreases, because the molecules of the solute become attached to the water molecules, making it more difficult for the water to form its crystaline shape and form into ice. This process is called Freezing Point Depression. In this experiment, you will be determining which of five salts most affects the Freezing Point of water.

Each salt will have a concentration of one mole. A mole is the atomic weight of the compound multiplied by one gram, in 1000 ml of water. Since you will be using only 100 ml of water each time, then you must divide the atomic weight by 10 before multiplying it by one gram. You will be using a computer-interfaced Temperature Probe to monitor how much each salt decreases the freezing temperature of water, and a graph of your results will be plotted using the computer.

*PURPOSE: To learn which type of salt lowers the Freezing Point of water the greatest amount.

*PROBLEM: Which type of salt lowers the Freezing Point of water to the lowest point?

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*HYPOTHESIS: The KCl will lower the water’s Freezing Point the most, because Potassium has the lowest ionization energy out of the five metals that are bonded with Chlorine, and perhaps it will bond more easily with the water molecules, keeping it from freezing.

*MATERIALS:

*Power Macintosh or Windows PC *10-ml graduated cylinder

*Vernier computer interface *ice

*LoggerPro *salt

*Vernier Temperature Probe *stirring rod

*ring stand *100 ml of 1M calcium chloride

*utility clamp *100 ml of 1M magnesium chloride

*one test tube *100 ml of 1M sodium chloride

*600-ml beaker *100 ml of 1M potassium chloride

*water *100 ml of 1M lithium chloride

*triple-beam balance *weighing dish

*PROCEDURES:

1. Put about 400 ml of water and only 5 to 6 ice cubes into a 600-ml beaker.

2. Obtain from your teacher 100 ml of 1M solution of each of the following solutions:

*CaCl *KCl

*MgCl *LiCl

*NaCl

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3. Using a graduated cylinder, measure and pour 5 ml of the CaCl solution into a test tube and use a utility clamp to fasten the test tube to

a ring stand. The test tube should be

clamped above the ice water bath.

Place the Temperature Probe into

the solution inside the test tube.

4. Prepare the computer for data collection by opening the Experiment 3 folder from Physical Science with Computers. Open the experiment file for the Stainless Steel Temperature Probe.