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COLLIGATIVE PROPERTIES
COLLIGATIVE PROPERTIES
Learning Objectives
Learning Objectives
Upon completion of this experiment, students will be able to:
(CLO1). Explain basic chemical concepts related to chemical changes, energy, and properties of matter.
(CLO2). Apply the methods of scientific inquiry
(CLO3). Analyze evidence to decide if generalizations or conclusions based on the obtained data are warranted
(CLO4). Interpret and utilize mathematical formulas while solving problems
(MLO 2) List, describe and perform calculations involving colligative properties: vapor pressure lowering, boiling point elevation, freezing point depression and osmotic pressure.
Use of cooling curves to determine melting points of both pure substances and mixtures when impurities are added to a pure substance
Experiment 27 explores the properties of solution and how the solvent's physical properties of vapor pressure, boiling point and freezing point change with the amount of solute added to the solution.
The assignments that must be completed are:
The assignments that must be completed are:
Complete the pre laboratory writing assignment before coming to the class meeting.
Attempt the pre laboratory problems by completing the assignment or the pre laboratory problems quiz in Canvas before coming to the class meeting.
Using the class data to complete the calculations to determine the molar mass of the unknown substance added to the cyclohexane for ALL trials of Part I and Part II
Complete the laboratory report, show how to calculate the values used to determine the molar mass of the unknown added to cyclohexane.
Complete the conclusion paragraph for this experiment.
Discussion
Discussion
The intermolecular forces that exist in pure substances allow us to understand how the physical properties are affected. In solutions, however, the intermolecular forces that exist between the solvent and solute can significantly affect several of the physical properties of the solvent. The four properties that are affected when a solute is dissolved in a pure solvent are the freezing or melting point, the boiling point, the vapor pressure and the osmotic pressure of the solvent. These are called the colligative properties. The melting point and boiling point are the temperature at which the substances changes its physical state, while the vapor pressure is the amount or partial pressure of gaseous substance that exists due to evaporation at a specific temperature in a closed system. These three colligative properties look at specific physical properties of the solvent and how those properties are changed when a solute is added. The fourth colligative property does not look at a specific property of the pure solvent but property due to the amount of solvent added to the solution. The osmotic pressure looks at how the process of osmosis is affected as the amount of solute is changed. Each of these properties can be modeled mathematically and the effect on each of these properties can be shown to be directly proportional to the amount or moles of solute in solution or the concentration of the solution.
The vapor pressure of a liquid is the partial pressure of the liquid contained above the liquid, due to evaporation, in a closed container. This property is affected by the strength of the intermolecular forces, the stronger the forces, the vapor pressure of the liquid is decreased. The vapor pressure of the solvent in a solution will be decreased because generally to make a solution, the intermolecular forces are stronger in the solution than in the pure solvent, thus, less of the solvent evaporates. This change in the vapor pressure can be calculated using Raoult's law
https://youtu.be/QEkFY3w80is
Freezing Point Depression
Freezing Point Depression
FlinnScientific - Lift an ice cube with a piece of string by sprinkling some salt on it!
This video is part of the Flinn Scientific Best Practices for Teaching Chemistry Video Series, a collection of over 125 hours of free professional development training for chemistry teachers - http://elearning.flinnsci.com
Vapor Pressure of Solutions III Computer Simulation
Vapor Pressure of Solutions III Computer Simulation
A computer simulation Determine how the physical properties of a solvent are dependent on the number of solute particles present. Measure the vapor pressure and osmotic pressure of pure water and a variety of solutions. Compare the effects of four solutes (sucrose, sodium chloride, calcium chloride, and potassium chloride) have the on the vapor pressure and osmotic pressure of a solution. Compare the solution's vapor pressure and osmotic pressure to the vapor pressure and osmotic pressure of pure water.
https://www.explorelearning.com/index.cfm?method=cResource.dspView&Resou...
©2017 Explore Learning. A Charlottesville, VA based company. Explore Learning is a Cambium Learning Company.
The phase diagram of the pure solvent and the resulting change to the vapor pressure when a solute can be seen in the figure.
The mathematical relationship of the freezing or boiling point colligative properties are determined from the same equation:
ΔT = k m,
where ΔT is the difference in the temperature of the pure solvent and the solution, k is the depression constant, either boiling point or freezing point, and m is the molality of the solution where
molality of solution, m = moles of solute mass of solvent in kg
where ΔT = |Tsolution - Tsolvent| (absolute value). The boiling point of the solution will be greater than the boiling point of the solvent (boiling point elevation) while the freezing point of the solution is less than the freezing point of solvent (freezing point depression).
Pre laboratory Writing
Pre laboratory Writing
Complete the pre laboratory writing assignment in your laboratory notebook. The prewriting must be completed before the laboratory session begins. The writing should include a purpose/hypothesis of the experiment, a discussion or theory, a detailed step by step summary of the procedure explaining what data will be collected and how you will collect it. Data Tables or space to collect the data should be included within the procedure discussion. Look up any SDS on chemicals that you are not familiar.
Pre laboratory assignments
Pre laboratory assignments
Attempt the pre laboratory problems either as the document provided in the experiment or as the laboratory quiz in canvas before coming to the class meeting.
Procedure
Procedure
A small amount of pure cyclohexane will be cooled in a salt water ice bath and the temperature will be measure until the liquid has completely frozen into the solid state. The cyclohexane will be weighed and a small amount of unknown will be dissolved in the cyclohexane and cooled in a salt water ice bath. The data will be collected using the MicroLab program and the 528 MicroLab Laboratory Data System. The Cooling curve graphs will be interpreted to determine the freezing point of both the pure and the mixture.
Use the MicroLab program which can be downloaded at https://microlabinfo.com/products-1/software.
Print and include your graphs in your report.
The experiment done by VladUlab for UH General II Chem Labs. There are 10 videos showing the steps to collecting the freezing point of cyclohexane and then the freezing point with naphthalene added.
Measuring 20 mL of cyclohexane
Weighing cyclohexane
Setup for freezing point
Frozen Cyclohexane
melting Cyclohexane
Weighing Naphthalene
Freezing point depression measurement
completed freezing point of mixture
Molar Mass by Freezing Point Depression Lab Video Explanation
Molar Mass by Freezing Point Depression Lab Video Explanation
nathanjones0117
This lab shows the explanation for a freezing point depression lab using different chemicals with the same results - determination of the molar mass of an unknown.
Another example of a Freezing Point Lab
https://youtu.be/06-o_t5qyio
Calculating Molar Mass from Freezing Point Depression
Calculating Molar Mass from Freezing Point Depression
webpage-http://www.kentchemistry.com/links/Ma...
This short video shows you how to calculate the molar mass of a nonelectrolyte (van't hoff=1) using freezing point depression.
Example Question:
The freezing point of a solution that contains 1.00 g of an unknown compound, dissolved in 10.0 g of benzene is found to be 2.07oC. The freezing point of pure benzene is 5.48 oC. The molal freezing point depression constant of benzene is 5.12 oC /molal. What is the molecular weight of the unknown compound?
Report and Conclusion Paragraph
Report and Conclusion Paragraph
Complete the data and result tables, graphs, calculations and answer all required questions.
Complete a conclusion paragraph using the RERUNS method. A discussion of how to write a conclusion paragraph is given in Appendix D: How to Write a Formal Laboratory Report
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