Today in chemistry we did a lab that tested the colligative properties. In the lab we boiled a solution of water and an unknown substance to its boiling point. We used four beakers that were each filled with about 50 ml of water. The first beaker was the control group so we didn't add any of the substance. In the second beaker we added about 5 grams of the substance and for the third and fourth beakers, we added about 10 and 15 grams respectively. While the solutions boiled we placed a thermometer inside the beaker to find its boiling point. As expected, the solution's boiling point got higher with a higher concentration of the substance. For the first calculation, you will want to use this equation:
T(b)=i x m x k(b)
You are supposed to solve for molality here. The ionic solid has 2 ions so i would equal 2. m would equal the molality and k(b) is a constant, which would be 0.51 for water. The T(b) is the Delta H that comes from the data in the lab. The homework is to finish up the post lab which is due on friday. Also there are 3 WebAssigns due on friday so keep up with them. The next scribe is Lauren C.
Showing posts with label colligative properties. Show all posts
Showing posts with label colligative properties. Show all posts
Wednesday, March 23, 2011
Tuesday, March 22, 2011
Colligative Properties
Today in chemistry we kicked off class with a lecture regarding colligative properties. There are 4 types of colligative properties and they are:
1.Vapor Pressure Lowering
2. Boiling Point Elevation
3. Melting Point Depression
4. Osmotic Pressure
Basically, the relations are simple. The more solute added, the more the vapor pressure decreases. The more solute added, the more the boiling point raises. The more solute added, the lower the melting point becomes. We also got a few formulas to accompany the above.
To calculate the change in boiling point(Blogger isn't letting me use equation editor, get notes off moodle to really see this):
Change in Boiling Point=molal boiling point elevation constant x molality
Traingle T subscript b= K subscript b * m
To calculate freezing point depression, you use the same formula except the constant is different. The K subscript b is repaced with K subscript f.
The van't Hoff factor basically mens that if you have a mole of NaCl, and the ions dissociate when in water, you will get one mole of Na+ ions and one mole of Cl- ions. The van't Hoff factor is i so simply modify the previous equations by multiply i to the end like so:
Triangle T subscript f= K subscript f * m * i
That pretty much sums it up for new material covered today. Liebs demonstrated these new concepts with one demo involving 4 of us as water molecules, showing that the more solute added (balloons), the more interactions we had to make with it (touching each ion), which made it harder for us water molecules to turn into our gaseous state. Also, we took some club soda, stuck it into some ice and upon opening the glass, thus releasing the CO2 which had raised the freezing point, the club soda immediately froze.
Liebs also discussed some issues with the faulty Webassign that was due today, and said he would make corrections. I know it probably frustated myself as much as did to some of you (honestly, comment if you remembered how to use sig figs before this unit started).
That's about all though. Homework tonight is to do all the worksheets you have been given this unit that are due on the day of the test, as well as the 3 remaining webassigns also due on the day of the test.
Justin J., come on down, you are the next contestant on the price is right.
1.Vapor Pressure Lowering
2. Boiling Point Elevation
3. Melting Point Depression
4. Osmotic Pressure
Basically, the relations are simple. The more solute added, the more the vapor pressure decreases. The more solute added, the more the boiling point raises. The more solute added, the lower the melting point becomes. We also got a few formulas to accompany the above.
To calculate the change in boiling point(Blogger isn't letting me use equation editor, get notes off moodle to really see this):
Change in Boiling Point=molal boiling point elevation constant x molality
Traingle T subscript b= K subscript b * m
To calculate freezing point depression, you use the same formula except the constant is different. The K subscript b is repaced with K subscript f.
The van't Hoff factor basically mens that if you have a mole of NaCl, and the ions dissociate when in water, you will get one mole of Na+ ions and one mole of Cl- ions. The van't Hoff factor is i so simply modify the previous equations by multiply i to the end like so:
Triangle T subscript f= K subscript f * m * i
That pretty much sums it up for new material covered today. Liebs demonstrated these new concepts with one demo involving 4 of us as water molecules, showing that the more solute added (balloons), the more interactions we had to make with it (touching each ion), which made it harder for us water molecules to turn into our gaseous state. Also, we took some club soda, stuck it into some ice and upon opening the glass, thus releasing the CO2 which had raised the freezing point, the club soda immediately froze.
Liebs also discussed some issues with the faulty Webassign that was due today, and said he would make corrections. I know it probably frustated myself as much as did to some of you (honestly, comment if you remembered how to use sig figs before this unit started).
That's about all though. Homework tonight is to do all the worksheets you have been given this unit that are due on the day of the test, as well as the 3 remaining webassigns also due on the day of the test.
Justin J., come on down, you are the next contestant on the price is right.
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