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4-8: Changes in the Boiling Point If you dissolve a substance such as ordinary table salt (NaCl) in water, the boiling point of the water will increase relative to the boiling point of the pure water. In this assignment, you will dissolve a sample of NaCl in water and then observe what happens when you continue to boil the water until the water boils away. 1. Start Virtual ChemLab, select Colligative Properties, and then select Changes in the Boiling Point from the list of assignments. The lab will open in the Calorimetry laboratory with a calorimeter on the lab bench and a sample of sodium chloride (NaCl) on the balance. 2. 100 mL of water is already in the calorimeter. Make certain the stirrer is On (you should be able to see the shaft rotating). Drag the weigh paper to the calorimeter and add the NaCl. Wait 30 seconds for the salt to dissolve and then turn on the heater by clicking on the green heater light on the control panel. Click the clock on the wall labeled Accelerate to accelerate the laboratory time if necessary. 3. When steam first appears, observe the temperature. Allow the solution to continue boiling and observe the temperature until all of the water boils away and the heater burns out. (The water level is shown on the right side of the calorimeter control panel.) What observations did you make about the temperature as the solution continued to boil? (3 points) 4. Explain the observations described in question # 3. Why does this occur? (5 points)

4-8: Changes in the Boiling Point
If you dissolve a substance such as ordinary table salt (NaCl) in water, the boiling point of the water will increase relative to the boiling point of the pure water. In this assignment, you will dissolve a sample of NaCl in water and then observe what happens when you continue to boil the water until the water boils away.
1. Start Virtual ChemLab, select Colligative Properties, and then select Changes in the Boiling Point from the list of assignments. The lab will open in the Calorimetry laboratory with a calorimeter on the lab bench and a sample of sodium chloride (NaCl) on the balance.
2. 100 mL of water is already in the calorimeter. Make certain the stirrer is On (you should be able to see the shaft rotating). Drag the weigh paper to the calorimeter and add the NaCl. Wait 30 seconds for the salt to dissolve and then turn on the heater by clicking on the green heater light on the control panel. Click the clock on the wall labeled Accelerate to accelerate the laboratory time if necessary.
3. When steam first appears, observe the temperature. Allow the solution to continue boiling and observe the temperature until all of the water boils away and the heater burns out. (The water level is shown on the right side of the calorimeter control panel.)
What observations did you make about the temperature as the solution continued to boil? (3 points)
4. Explain the observations described in question # 3. Why does this occur? (5 points)

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