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Discussion: Colligative Properties. Students will be able to: Explain how dissolved solutes affect the boiling and freezing points of solutions. Remember. Packet # 1 is due today Lab next time! . The Affect of Adding Non-volatile Solutes. - PowerPoint PPT Presentation
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Discussion: Colligative Properties
Students will be able to:Explain how dissolved solutes affect the boiling
and freezing points of solutions
Remember
Packet # 1 is due today
Lab next time!
The Affect of Adding Non-volatile Solutes
What happens to the boiling point and freezing point as solutes are added?
Will the Freezing Point Ever Go Up?
NO! Adding Solutes Will Always Make the Freezing Point Go Down
Will the Boiling Point Ever Go Down?
Sometimes. If the solute is volatile the boiling point goes down.
An example would be adding alcohol to water. The mixture will boil at a lower temperature than the pure water.
The boiling point of alcohol is only around 70oC so adding it makes the boiling point go down
Ice Will Not Melt if the Outside Temp is Lower than Zero
Since the Fp = 0 and the outside temp is -5, this ice won’t melt.
If the Outside Temperature is -5oC Salt and Ice Mixtures Can Melt
If you can add salt the mixture will not freeze until it is -10oC
Why do people add salt to roads?
Sentence #1:
Sentence #2:
Sentence #3:
Colligative Properties
What are two properties of solutions that depend on the number of dissolved particles?
Boiling Point (normally goes up) Freezing Point
Ethylene Glycol
This is the molecule that is commonly called antifreeze. C2H6O2
62 grams/mol There are two reasons it is used for
antifreeze. It has
a high boiling point and it is very soluble in water
Antifreeze
Why is antifreeze added to cars? The mixture of water and ethylene
glycol has a higher boiling point than pure water.
The mixture of water and ethylene glycol has a lower freezing point than pure water.
Molarity and molality
Molarity is the ratio of moles solute to liters of solution
Molality is the ratio of moles solute to kilograms of solvent
Notice you divide by the solvent not the solution
Calculate Molality (on discussion)
30.0 grams of C2H6O2 (the solute) change to moles
Mixed with 30.0 grams of water (the solvent)change to Kg
What Temp Will it Freeze?
What are the two factors that influence how much it drops? a. the molality of the solution b. the freezing point constant of water (1.86)
Identify The Symbols
How to Calculate the Boiling Point
ΔTb = m x Kb ΔTb = m x 0.512 ΔTb = 16.13 x 0.512 8.25 Recall the temp of boiling goes up. Boiling
is normally 100oC. So the temp of boiling is……
108.25
70 grams of water (the solvent) mixed with 30 grams of
antifreeze (C2H6O2) the solute.