Chem 162 Lab 4

Intermolecular Forces

vapor pressure apparatusThere are two parts to this lab. The objective of Part I is to understand the effect of intermolecular and intramolecular forces on melting points and acid dissociation constants. In Part II, the objective is to measure the enthalpy of vaporization for four organic compounds and describe the intermolecular bonding energy of each compound in terms of the dispersion and polar components.

 

In Part I of this experiment, you will examine the potential for Hydrogen bonding for the cis and trans versions of HOOCCH=CHCOOH, also known as maleic acid and fumaric acid, respectively. Based on what you know about Hydrogen bonding, and from the three-dimensional model that you will build of each molecule, you will determine how Hydrogen bonding is expected to affect the melting point, solubility, and Ka values for these molecules. You will be asked to predict which of these two substances has a higher melting point and higher Ka1 value. Then you will be given the two substances, labeled "A" and "B," and asked to determine which substance is which based on your data from measuring the melting point and pH of each substance and your examination of the molecular models.

 

In Part II, you will use a vapor pressure apparatus to measure the change in vapor pressure as a function of temperature for each of four organic compounds provided. The "Vapor Pressure and Changes of State" section in the Zumdahl text explains the quantitative evaluation of the temperature dependence of vapor pressure. In short, a plot of ln Pvap vs 1/T, where T is the temperature in Kelvin, will yield a straight line with a slope related to the enthalpy of vaporization and y-intercept related to the entropy of vaporization. After solving for the enthalpy, you will be able to determine how much of the intermolecular bonding energy is due to polar forces versus dispersion forces.

 

  • Prelab
    • Intro (pdf 205 KB, rev 10/7/12)
    • Required Prelab Assignment in Canvas (due Tuesday 7/30 at 11:30 am)
    • Review Materials & Procedure
    • Review Demonstration

 

 

 

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