1 Chemistry Name:__________________ Period: ____ Colligative Properties and Types of Solutions Packet 12 Day In Class Work 1 Molality 2 Freezing Point Depression 3 Freezing Point Depression Lab 4 Boiling Point Elevation 5 Test 6 Ice Cream Lab Outcomes 1. Solve freezing point depression problems 2. Solve boiling point elevation problems 3. Write an essay on the ice cream experiment explaining the principles of freezing point depression and types of colloids.
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1
Chemistry
Name:__________________
Period: ____
Colligative Properties and Types of Solutions
Packet 12
Day In Class Work 1 Molality
2 Freezing Point Depression
3 Freezing Point Depression Lab
4 Boiling Point Elevation
5 Test
6 Ice Cream Lab
Outcomes 1. Solve freezing point depression problems
2. Solve boiling point elevation problems
3. Write an essay on the ice cream experiment explaining the principles of freezing point
depression and types of colloids.
2
In Packet 11 we will investigate colligative properties and colloidal properties of matter.
Colligative properties are properties of solutions that depend on the number of particles in a
given volume of solvent and not on the mass of the particles. Colligative properties include:
lowering of vapor pressure; elevation of boiling point; depression of freezing point; osmotic
pressure.
MOLALITY The molality of a solution is calculated by taking the moles of solute and dividing by the
kilograms of solvent.
Example - What is the molality when 0.75 mol is dissolved in 2.50 kg of solvent?
The answer is 0.300 m.
Complete the following questions and problems relating to molality.
1) Write the equation for molality:
2) Write the equation for molarity:
3) Explain in words how molality and molarity differ.
4) What is the molality of a solution in which 0.32 moles AlCl3 has been dissolved in 2,200 g
water?
5) What is the molality of a solution in which 0.60 mol propyleneglycol are dissolved in 2kg of
water??
6) What is the molality of a solution in which 0.145 mol CO2 (molar mass = 44.01
g/mol) is dissolved in 591 g water?
7) What is the molality of a solution in which 13.7 g NaCl has been dissolved in
500.0g water?
8) How many grams of ethanol, C2H6O (molar mass 46.08 g/mol), are need to prepare a 0.10
4. A water solution is found to have an actual boiling point of 100.85°C. What is the
molality of the solution?
5. A solution of iodine in benzene is found to have an actual boiling point of 81.9°C. What
is the molality of the solution?
6. A solution is prepared by dissolving 24.2 grams of sugar in 200grams of water. What is
the actual boiling point of the solution?
7. A benzene solution is found to have an actual boiling point of 83.9°C. What is the
molality of the solution?
Review
1. Calculate the actual freezing point of 1.25m solution of KCl in water.
2. Calculate the boiling point elevation of 0.5m solution of KCl in phenol
3. Calculate the actual freezing point of a 1.35m solution of NaCl in benzene.
4. Calculate the freezing point depression of a 2.4m solution of NaCl in water.
5. Calculate the boiling point elevation of a 1.75m solution of KCl in camphor.
6. Calculate the molality of phenol in a solution if the actually freezing point is 37.5°C.
11
Boiling Point Elevation
Boiling point elevation occurs when the boiling point of a solution becomes higher than the
boiling point of a pure solvent. The temperature at which the solvent boils is increased by adding
any non-volatile solute. A common example of boiling point elevation can be observed by
adding salt to water. The boiling point of the water is increased.
Purpose: Determine the boiling point of pure water, salt water and sugar water.
Procedure:
1. Get the mass of 150ml of water and place it in a 250ml beaker.
2. Suspend a thermometer in the 250ml beaker so it sit in the middle of the water and record
the temperature.
3. Light the Bunsen burner and record the temperature of the water every 30 seconds for 8
minutes in the data table below.
4. Discard the water.
5. Measure out 2 grams of NaCl and place it 150ml of water. Place the solution in a 250ml
beaker. Repeat step 2 and 3 for the salt water solution.
6. Discard saline solution
7. Measure out 2 grams of sugar and place it in a 150ml of water. Place the sugar solution
in a 250ml beaker and repeat steps 2 and 3.
8. Discard sugar solution
Data:
Time (min) Pure Water
(°C)
Saline Solution
(°C)
Sugar Solution
(°C)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Mass of 150ml of water ______ Mass of salt _______ Mass of sugar ______
Kilograms of water ______ Moles of Salt ______ Moles of sugar ______
Molality of Salt Water ____________ Molality of Sugar Water __________
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Graph the information from the Data Table
Calculations:
What is the accepted boiling point of water?
What is the experimental boiling point of water?
Percent Error?
ΔTbp = Kbpm
What is the accepted boiling point of salt water?
What is the experimental boiling point of salt water?
Percent Error?
ΔTbp = Kbpm
What is the accepted boiling point of sugar water?
What is the experimental boiling point of sugar water?
Percent Error?
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Colligative Properties
PART A – CALCULATIONS
1. Indicate how many ions are formed when the following solutes dissolve.
SOLUTE # OF IONS SOLUTE # OF IONS
sucrose (C12H22O11) magnesium chloride (MgCl2)
sodium sulfate (Na2SO4) methanol (CH3OH)
2. When 5.0 g of CaCl2 dissolves in 50.0 g of water, what is the boiling point of the solution?
GIVEN WORK
3. Find the boiling point of a solution containing 6.0 g benzene, C6H6, in 35 g of napthalene.
GIVEN WORK
4. Mrs. J’s feet are aching at the end of a long day. At home, she dissolves 26.0 g of Epsom salt, MgSO4, in 1.5 kg of water. What is the freezing point of this solution?
GIVEN WORK
PART B – APPLICATIONS (Answer the following questions on the back of this paper.)
5. Salt is often used to remove ice from roads and sidewalks. Explain how this process works in terms of colligative properties.
6. Which salt, NaCl or CaCl2, has a greater effect on freezing point? Explain.
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The CHEMISTRY of Ice Cream
Who knew chemistry could be so tasty! Today we will be investigating colligative properties
and how they affect freezing points, and some yummy results of energy changes.
Pre-Lab questions:
1. What is freezing point depression?
2. Is freezing an exothermic or endothermic process?
3. Is melting an exothermic or endothermic process?
4. How does energy flow? (from where to where?)
OBJECTIVES:
Investigate the effects of temperature change on phase changes
Investigate the effects of changes in freezing point
Utilize the law of conservation of energy
Apply these concepts to make ice cream!
RECIPE:
Ingredients:
Write your final recipe here. It must be approved before you begin.
Analysis:
1. What state of matter was the milk when you began?
2. What state of matter was the milk when you were done?
3. In order to change the phase of the milk, what had to be removed?
4. What happened to the heat energy that left the milk?
5. Why was salt added to the ice?
6. If you did not add sugar, would the ice cream freeze faster or slower? Why?
Explain, using your knowledge of chemistry.
7. Describe the transfer of energy that occurred in this lab.
8. How could you improve your recipe?
15
Colligative Properties Worksheet
Complete the following questions and problems relating to colligative properties.
1) Write the mathematical expression for boiling point elevation. Define all of the terms used.
2) Write the mathematical expression for freezing point depression. Define all of the terms
used.
3) When sugar is dissolved in water, will the resulting solution boil at a higher or lower
temperature than pure water? Explain.
4) When salt is dissolved in water, will the resulting solution freeze at a higher or lower
temperature than pure water? Explain.
5) What is the change in boiling point (vs. pure water) of a 1.25 molal solution of sugar in
water? The Kb for water is 0.52oC/m.
6) What is the change in freezing point (vs. pure water) of a 0.78 molal solution of NaCl in
water? The Kf for water is 1.86oC/m.
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7) A solution was prepared by dissolving 0.42 mol hexane into 500g CCl4. What is the change
in freezing point (vs. pure CCl4) of this solution? The Kf for CCl4 is 30.0oC/m.
8) A solution was prepared by dissolving 0.16 mol ethanol into 750g ether. What is the change
in boiling point (vs. pure ether) of this solution? The Kb for ether is 2.02oC/m.
9) A solution of propylene glycol (antifreeze) in your car’s radiator has a freezing point of –
20oC. What is the molality of the solution? Kf for water is 1.86
oC/m.
10) In order to make spaghetti cook faster, a chef adds salt to water. How many moles of salt
would he need to add to 1.0 kg water to make the water boil at 105oC? The Kb for water is
0.51oC/m.
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Colligative Properties Worksheet
1. For a 0.222 m aqueous solution of sucrose, C12H22O11, What is the boiling point?
2. What is the normal boiling point of a 0.122 m aqueous solution of KI?
3. Automotive antifreeze consists of ethylene glycol, C2H6O2 , a nonvolatile nonelectrolyte.
Calculate the boiling point and freezing point of a 25.0 mass percent solution of ethylene
glycol in water.
4. Calculate the freezing point of a solution containing 0.600 kg of CHCl3 and 42.0 g of
eucalyptol9 C10H18O), a fragrant substance found in the leaves of eucalyptus tree. Kf=
4.68 0c/m, normal freezing point = -63.5
0c
5. List the following aqueous solutions in order of their expected freezing points: 0.050 m
CaCl2; 0.15 m NaCl; 0.10 m HCl; 0.050 m HC2H3O2; 0.10 m C12H22O11
6. A solution of an unknown nonvolatile nonelectrolyte was prepared by dissolving 0.250 g
in 40.0 g CCl4. The normal boiling point of the resultant solution increased by 0.3570C.
Calculate the molar mass of the solute. Kb= 5.02 0c/m
7. Camphor, C10H16O, melts at 179.8 o C, it has particularly large freezing point depression
constant, Kf = 400C/mol. When 0.186 g of an organic substance of unknown molar mass
is dissolved in 22.01 g of liquid camphor, the freezing point of the mixture is found to be
176.7 0C. What is the approximate molar mass of the solute?