Objectives:
1. Describe what happens on a particle level at the boiling point of a liquid.
2. Determine boiling point temperatures using a vapor pressure curve; compare and contrast intermolecular forces of a substance using the data on a vapor pressure curve.
3. Explain on a particle basis why a solution has a lower vapor pressure, an elevated boiling point, and a depressed freezing point, compared to that of the pure solvent.
4. Calculate the molality (m) of a solution, moles of solute or kilograms of solvent given the other 2 variables; calculate the change in boiling point or freezing point temperature based on the molality (m) of a solution.
Here's a video describing vapor pressure and boiling:
A series of curves on one set of axes can be shown. Here is one graph used in NYS Regents Chemistry:
http://drgchemistry.weebly.com/uploads/2/4/8/9/24894932/topic_4_-_vapor_pressure.pdf
Here's a lab to determine the vapor pressure of water at various temperatures so that students can graph it. I like that it's pretty reasonable to gather the materials and to perform.
http://phs.prs.k12.nj.us/rcorell/VaporPressureWaterLab.pdf
Remember eye safety goggles and aprons
Here is a lecture about intermolecular forces and the effect on boiling point temperature. The discussion is very fast but very comprehensive -- you may have to view it more than once to better follow this discussion:
You may wonder about why all this talking about vapor pressure and boiling? Because a solute has an effect on boiling point and freezing point. This is a video demonstrating solute affecting boiling point and freezing point. This seems to be a student video and has a few misspellings -- oops!
http://www.cliffsnotes.com/sciences/chemistry/chemistry/solutions/freezing-and-boiling-points
But wait! What is molality? You may remember my discussion Molarity a few days ago. Here is a brief discussion (5 minutes) of molarity (M) vs. molality (m):
http://www2.hoover.k12.al.us/schools/hhs/faculty/jwalding/Worksheets/Molality.pdf
Here is a worksheet with answers and strategy suggestions:
http://www.horton.ednet.ns.ca/staff/richards/apchemistry/APAssignments/SolutionsAss4AnswerKey.pdf
Salt lowering the freezing point temperature of ice has a few practical applications. It is commonly used on icy roads and sidewalks to lower the freezing point temperature and prevent ice formation.
States are trying a variety of solvents other than salt to save money. Here's Massachusetts' webpage that contains a table of the salt fighting substances:
https://www.massdot.state.ma.us/highway/Departments/SnowIce/WinterRoadTreatmentSnowRemoval.aspx
For making ice cream, salt is mixed with the ice surrounding the system to lower its temperature and aid in freezing the cream/sugar mixture.
Here is an easy way to make ice cream using salt and ice:
Check out my lab book "Chemistry on a Budget" at amazon.com:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget
Each lab is presented with two possible report formats -- both with the same procedure -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This was to give the teacher the option of what type of report is desired!
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Have a good end of the week!