Taught aggressively and with a loud voice WOOOAAAHHHHH The wood frog is a remarkable creature because it can survive being frozen Scientists believe that a substance glycerin and glucose ID: 569346
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Slide1
Colligative properties
Taught aggressively and with a loud voiceSlide2
WOOOAAAHHHHH
The
wood frog is a remarkable creature because it can survive being frozen. Scientists believe that a
substance (glycerin and glucose) in the cells of this frog acts as a natural antifreeze, which prevents the cells from freezing. You will discover how a solute can change the freezing point of a solution.
http://newswatch.nationalgeographic.com/2013/08/21/how-the-alaska-wood-frog-survives-being-frozen/Slide3
What is a colligative property?
A property that depends ONLY upon the
number
of solute particles, and not upon their identity. So what does that mean?“I don’t care who you are or what you look like! I don’t care what you are made of! I just need a lot of ANYBODY to get this done!”Slide4
Therefore,
The amount of solute particles is the only thing that affects colligative properties, and colligative properties apply to all types of substances– no matter what they are made of.
Examples of Colligative Properties:
Freezing-Point Depression (If you freeze now… that’s it. It’s over! Don’t you dare freeze on me!)Boiling-Point Elevation
(No! Don’t boil yet! Hold on! Wait!)Vapor Pressure Lowering ( Do not vaporize as much as you are! You are not as volatile as you think!)Slide5
Activity
An ice storm is coming. Your car’s radiator has no antifreeze in it; all stores are closed, and you’ve got to use whatever you have around the house to keep the water from freezing in the car’s engine and splitting the engine block.
Rule one:
What you add has to dissolve in water.
Rule two: If you add a solid or liquid that dissolves in water, it doesn’t matter what it is, just the amount.
Rule three:
Just like antifreeze, your goal is to replace about ½ of the water with a solid or liquid that is miscible with water.Slide6
The
items on the left is what you had. So you mixed all of these into a gallon of water and poured it into your radiator.
Note:
This is where it doesn't matter what substance you use. It's the count (the moles) that matters, not its chemical
makeup.It was a long cold night and the next morning you wonder if what you did saved you thousands of dollars on a new engine….Slide7
But your car looks like this…
So after a few days, the ice thaws and you check your engine. It worked! It didn’t freeze! Of course, you now replace your mixture with actual antifreeze from the store.
Hmmm… How does antifreeze lower the freezing point of the water? Slide8
1) Freezing Point Depression
The difference in temperature between freezing point of the solution and the freezing point of the pure solvent.
Freezing point of Solution is a LOWER temperature than freezing point of pure solvent.Slide9
WHY??
Reason 1:
As the water tries to freeze, the other molecules get in the way.
Reason 2: By adding these other substances, you’ve added disorder to the mixture. Nature tends to favor disorder (entropy). When water tries to freeze, it has to get organized, which will be more difficult because it’s mixed with all of these other molecules.Slide10
Order and ENTROpy
Pure substances are more orderly. When mixed, they lose that order and become more random (more entropy). Again, nature favors entropy.
You know entropy from experience. You may clean and organize your room, but it doesn't seem to take long for everything to become disorganized and cluttered. It takes energy to organize and reduce clutter. It seems easy to make it disorganizedSlide11
Other Freezing point depressions
Eggs are mostly water, but dissolved proteins keep them from freezing at 0°C
.
Chefs take advantage of this in frozen desserts.Slide12
Notice that ice cream melts differently than ice. Ice stays hard until it melts. Ice cream gradually get softer and softer.
Ice is a pure substance but ice cream is a mixture. In other words, there are other chemicals that get in the way of ice freezing. So you
have to
get colder than 0°C to get it to freeze.About 30% of the water in ice cream never freezes because of the high level of dissolved solids like sugar, fats, and proteins.Slide13
2) Boiling Point elevation
Antifreeze is also called a coolant because it will
raise
the temperature at which a liquid will begin to boil.Why is this a good thing?Slide14
2) Boiling Point elevation
The
difference
in temperature between the boiling point of solution and the boiling point of the pure solvent. Boiling point of solution is HIGHER than boiling point of pure solvent. Slide15
WHY??
By adding non-volatile substances, it interferes with the particles and lowers the vapor pressure.
Therefore, MORE energy such as heat must be added to push those particles to boil.Slide16
3) Vapor Pressure lowering
In a solution,
solute
particles reduce the number of free solvent particles able to escape the liquid.
The more solute particles you add to the solution, the lower the vapor pressure will be.Slide17
Remember
Colligative Properties DO NOT depend on the actual particle.
It only depends on the AMOUNT of particles.Slide18
problem
In college,
I stored sodas in a small refrigerator. One day I noticed that the Diet Coke had exploded from freezing but the regular Coke did not freeze and therefore did not explode. I thought why did the Diet Coke freeze and not regular Coke? Slide19
Solution
Regular coke has about 39 grams of sugar dissolved in it. Diet Coke has only about 0.1 gram of Aspartame sweetener in it. The 39 grams of sugar interfered with the water trying to freeze. So the freezing point of regular Coke was lower than that of Diet Coke. Diet Coke's freezing point is basically the same as water since very little is dissolved in Diet Coke.Slide20
Calculations involving colligative properties
Review:
We learned that to calculate the concentration of a solution, we can use molarity.
Molarity = M = mol/LSlide21
Molality
Molality is a different way to calculate the concentration of a solution.
It is represented by a little m.Slide22
Calculate molality
What is the molality of a solution that is made by adding 29.3g
NaCl
to 1000 g of water?Slide23
Calculating grams from molalitySlide24
Relating Concepts
How are freezing-point depression and boiling-point elevation related to molality?
Freezing Point Depression
Boiling Point ElevationSlide25
What is the normal freezing point of water before adding a solute? Slide26
What is the normal boiling point of water before adding a solute?Slide27
Practice Problems
Anything that can be is used to depress the freezing point of water can also be used to cause ice to melt.
Here is your ice covered Porsche after an ice storm.What substances could you use to de-ice
it?Slide28
Practice problems
The
ingredients say 39 grams
of sugar is used in 1 can of coke.The molar mass of fructose (sugar) is 180.16 g/mol. 1 can =12 oz = 355
mL.= about 355 g of solutionKf= 1.86 C·kg/mol
for water
.
Question: So
how many degrees Celsius does the sugar reduce the freezing point of water in the can
?
What is the new boiling point?Slide29
Practice Problems
How many grams of sodium bromide must be dissolved in 400.0g of water to produce a 0.500
molal
solution?