Boiling
Point Change Lab – 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 it’s 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 don’t, 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 CaCl2 was put into
water, how many moles of Ca and Cl did you have total?