12: LAB 12 - AN INVESTIGATION OF INTERMOLECULAR FORCES
- Page ID
- 506225
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The purpose of this experiment is to:
- Identify intermolecular forces present in the given liquids.
- Test the solubility of various liquids in water.
- Explore the evaporation of liquids and relate the results to the strengths of intermolecular forces.
INTRODUCTION
Intermolecular forces are attractive forces between atoms and molecules in a substance. The three most important intermolecular forces are London dispersion forces, dipole-dipole, and hydrogen bonding. We first look at the polarity to determine the primary intermolecular force present in a substance. Polar substances will have dipole-dipole or hydrogen bonding as the primary intermolecular force, and non-polar substances will have London dispersion forces.
Intermolecular forces play a pivotal role in determining the physical properties exhibited by substances. For instance, they can explain why certain substances form solutions with others. Understanding these forces also enables us to predict trends in boiling points and evaporation rates of liquids based on their strengths.
In this experiment, you will first identify the most important intermolecular force in various liquids by examining their structure and polarity. You will then be asked to perform a literature search to determine the boiling point of each liquid. Finally, you will explore how intermolecular forces influence solution formation and evaporation.
1) Always wear chemical splash goggles while working on this experiment.
2) Gloves are provided for you if you wish to wear them.
3) Work with all chemicals in a well-ventilated area or under a fume hood.
4) At the end of the experiment, dispose of all used chemicals in the appropriate waste container.
5) Wash and return all glassware to the appropriate place.
6) Thoroughly clean your work area before leaving the lab.
7) Wash your hands as soon as you leave the lab.
EQUIPMENT* AND CHEMICALS NEEDED
| EQUIPMENT | CHEMICALS | CHEMICALS |
|---|---|---|
| Well plate | Deionized water | Ethyl acetate |
| 600 mL beaker | Methanol | Butyl acetate |
| 7 small test tubes | Ethanol | Hexane |
| Test tube rack | Isopropyl alcohol | Non-halogenated organic waste container |
| Thermometer | 1-butanol | - |
* Images of equipment needed in this lab can be found in the appendix (the equipment may differ or be subject to changes; follow your instructor’s directions).
EXPERIMENTAL PROCEDURE
Part A: Properties of liquids
For each of the liquids used in this experiment, draw the appropriate Lewis structure, predict whether the substance is polar or non-polar, determine the molar mass, identify the most important intermolecular force present, and do a literature search to find the boiling point (in oC). Record all this information in the data table.
Part B: Solubility
Obtain seven small test tubes and a test tube rack. To each test tube, add 1 mL of deionized water. Then, add 1 mL of the given liquids to the following test tubes:
Test tube 1 = methanol
Test tube 2 = ethanol
Test tube 3 = isopropyl alcohol
Test tube 4 = 1-butanol
Test tube 5 = ethyl acetate
Test tube 6 = butyl acetate
Test tube 7 = hexane
Gently shake each test tube and determine whether each liquid is soluble in water. Record your observations in the data table. Dispose of the contents of each test tube in the non-halogenated organic waste container.
Part C: Evaporation
1) Half fill wells in a Well plate with each liquid (deionized water, methanol, ethanol, isopropyl alcohol, 1-butanol, ethyl acetate, butyl acetate, and hexane).
2) Determine the initial temperature of the deionized water using a Celsius thermometer or the temperature probe with LabQuest. Be sure to hold the thermometer in the liquid until the reading stabilizes.
3) Once the initial temperature has been recorded, remove the thermometer from the water and hold it in the air. Once the temperature stabilizes, record the final temperature.
4) Repeat this procedure for each liquid.
5) Once you have completed this procedure, pour the contents of the well plate into a 600 mL beaker and then transfer the beaker's contents into the non-halogenated organic waste container.
PRE-LAB QUESTIONS
Name ___________________
- Define the following terms:
Part A: Intermolecular forces
Part B: London dispersion forces
Part C: Dipole-dipole
Part D: Hydrogen bonding
- Match and write the correct intermolecular force (London dispersion force, dipole-dipole, or hydrogen bonding) to each description.
Part A: Intermolecular force that is present when hydrogen is directly bonded to oxygen, nitrogen, or fluorine:
Part B: The strongest of the intermolecular forces:
Part C: The weakest of the intermolecular forces:
Part D: The most important intermolecular force present in HCl:
Part E: Intermolecular force based on a temporary attractive force:
- What are three factors that affect the strength of intermolecular forces?
- Circle the best choice (indicated in the parenthesis) for each question:
Part A: Substances with stronger intermolecular forces tend to have (higher/lower) boiling points and evaporate (more readily/less readily) than substances with weaker intermolecular forces.
Part B: Substances with similar intermolecular forces tend to be (miscible/immiscible) with each other.
DATA AND OBSERVATIONS
Name _______________________ Lab Partner(s) __________________________
Part A: Properties of Liquids
*Substance |
Molar Mass |
Boiling Point |
Lewis Structure |
Polar or Nonpolar |
Primary Intermolecular Force |
|---|---|---|---|---|---|
|
Water [H2O] HOH
|
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Methanol [CH4O] CH3OH
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Ethanol [C2H5OH] CH3CH2OH
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Isopropyl Alcohol [C₃H₈O] CH₃CHOHCH₃
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1-butanol [C4H9-OH] (CH3(CH2)2CH2-OH)
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Ethyl Acetate [C₄H₈O₂] CH₃COOCH₂CH₃
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Butyl acetate [C₆H₁₂O₂] CH₃COO(CH₂)₃CH₃
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Hexane [C6H14] CH3(CH2)4CH3
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*Name, [Chemical Formula], and Condensed Formula (Showing Connectivity).
Part B: Solubility
Liquid |
Soluble or Insoluble in Water? |
|---|---|
|
1-butanol |
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Butyl acetate |
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Ethanol |
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Ethyl acetate |
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Hexane |
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Isopropyl alcohol |
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Methanol |
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Part C: Evaporation
Liquid |
Initial Temperature |
Final Thermometer Reading |
Change in Temperature |
|---|---|---|---|
|
Water |
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Methanol |
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Ethanol |
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Isopropyl alcohol |
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1-butanol |
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Ethyl acetate |
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Butyl acetate |
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Hexane |
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POST-LAB QUESTIONS
- Refer to the results from part A. What is the relationship (if any) between the molar masses and boiling points of the liquids?
- Refer to the results from part A. Do you notice a trend between the boiling points and primary intermolecular forces in the liquids?
- Refer to the results from part B. What type of substances were soluble in water? How can you use the concept of intermolecular forces to explain this?
- Refer to the results from part B. Explain why this was the case for each substance insoluble in water.
- Write a summary of the results from part C.
- Is there a connection between the observed evaporation results of the liquids in part C and the boiling points recorded in part A? Explain.
- Based on the results from part C, is evaporation an endothermic or exothermic process? Explain.
- Based on the results of this experiment, what can you conclude about the relationship between the strengths of intermolecular forces and the boiling points/evaporation of a liquid?
Please click here to access the Pre-Lab, Data Tables, and Post-Lab in Word or PDF format. Complete them and upload according to your instructor's instructions.