Part I- Determining the Freezing Point Depression 1) Place 10-mL distilled or de

Question

Part I- Determining the Freezing Point Depression 1) Place 10-mL distilled or deionized water into an 8-inch test tube. Insert the stirring apparatus as shown below. Make sure the thermometer bulb is immerged in the liquid. 2) Place the entire apparatus in a prepared salt-water bath Allow the water to cool with continuous stirring until there is ice-water slush in the tube. Thermometer Stirrer solution Ice-sat water cork 3) Remove the test tube from the bath. Stir vigorously and note the constant temperature during the time that both ice and water are present. This is the freezing point of pure water. Record this value in your notebook. 4) Discard the water. Repeat the procedut freezing point of the solution in your notebook. Once you have determined the freezing point of the 10% sodium chloride solution, discard the solution and rinse the tube out with water to clean it. 5) Repeat the procedure with the 10% methanol solution. Record the freezing point of the solution in your notebook. Once you have determined the freezing point of the 10% methanol solution, discard the solution in the appropriate waste container in the fume hood 6) Clean your apparatus.

Explanation / Answer

In the first case there is a pure water placed in the test tube. Therefore the freezing point is 0°C.

In the second case the solution in the test tube is 10% NaCl. Due to addition of salt , the freezing point of the pure water decreases upto -20°C. This is called as depression in freezing point . It depends on the nature of solute.

In the third case the solution in test tube is 10% methanol. And the freezing point reading is approximately- 7°C.

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