Boiling Point Change Lab Ė 10 points

Purpose: to predict the boiling point change in water when you add NaCl and when you add CaCl2

 

Remember: The formula for finding boiling point change is: DTb=kbm x (number of particles)

The kb for water is: 0.51 oC kg/mol.

 

Pre-Lab:

Determine the DTb of water if you were to add the following amounts of salt to water:

1. Add 2.93 g of NaCl to 25.0 ml. of water. _________________DTb

2. Add 5.55 g of CaCl2 to 25.0 ml. of water. ________________DTb

 

Procedure:††† Note, if I have enough small glassware bottles, you can do all three samples at once.Use the same thermometer in all three samples!Why?

1.†† Measure out 25.0 ml. of distilled water into a small beaker.

2.†† Bring the water to a boil on a hot plate.

3.†† Record the temperature of the boiling water on your data table. This is ACTUAL TEMPERTURE OF PURE BOILING WATER.(use a hot-hand to tip the beaker over on itís side a little bit if you are having trouble submerging the bulb of the thermometer completely in the water)

 

Safety First:NEVER put dry salt into water which is currently boiling.ALWAYS put the salt in BEFORE you heat the water.If you donít, the water will boil up when you add the salt to it and it could splash boiling water all over you!

 

4.†† Measure out 2.93 g of NON-IODIZED salt and place it in a small beaker.

5.†† Add 25.0 ml. of distilled water and boil the salt/water mixture. Record this as ACTUAL TEMPERTURE OF NaCl WATER.

 

6.†† Measure out 5.55g of CaCl2 and place it in another small beaker.

7.†† Add 25.0 ml. of distilled water and boil the salt/water mixture. Record this as ACTUAL TEMPERTURE OF CaCl2 WATER.

 

Data Table:

ACTUAL TEMPERTURE OF PURE BOILING WATER†† __________ oC

ACTUAL TEMPERTURE OF NaCl WATER ________________oC

ACTUAL TEMPERTURE OF CaCl2 WATER _______________oC

 

QUESTIONS:

1. Why do you need to use distilled water in this experiment?

 

2. Why do you need to heat pure water first and take its temperature? We know that the temperature of pure water is 100 oC, so why do we have to do this first.

 

3. Why do you think you need to use NON-IODIZED salt when preparing the NaCl solution?

 

4. How many moles of NaCl Did you use?

 

5. How many moles of CaCl2 Did you use?

 

6. Once the NaCl was put into water, how many moles of Na and Cl did you have total?

 

7. Once the CaCl2was put into water, how many moles of Ca and Cl did you have total?