THE EFFECT OF COMPOSITION ON SEVERAL PHYSICAL PROPERTIES OF BINARY MIXTURES OF COMMON LIQUIDS
The effect of the composition of solutions on their physical properties has been an important focus of both experimental and theoretical investigations in physical chemistry for many years. This multipart project involves the determination of the effect of composition on the partial molar volume, viscosity and surface tension for a binary mixture. Appropriate selection of components for the mixtures insures interesting variations in these properties with composition. Comparison of the whole range of properties invites a consistent interpretation of the observed composition dependence of these properties at the molecular level.
The entire project can be completed in two or three 3-hour laboratory periods with students working in groups. An additional period is allocated to complete workup of the data and preparation of a formal report. Coming early in the first semester of the course, the workup of the data provides a good introduction to (or review of) the use of spreadsheet software and computer graphing of data. A powder-point presentation will be made for comparison of results among the groups and to provide opportunities for students to give oral reports on their investigations.
Preparation of Mixture Solution
- Two binary mixture solutions will be studied in this project and each group will be assigned to study one mixture. A series of such binary solutions of 100 ml need to be prepared at the beginning of the project. Please follow the instruction below to make corresponding solutions.
- Prepare a series of ethanol-water mixture (for mixture 2, different liquids should be used) according to the following steps:
- Weigh a clean and dry 100-mL volumetric flask on the analytical balance.
- Use a graduated cylinder to obtain 20 mL of ethanol and add it to the flask. Record the actual mass. (You may use stopper if reading is not stable due to evaporation.)
- Fill the volumetric flask with deionized water until the liquid level reaches 100-ml mark. Shake the mixture gently. Reweigh the flask and record the actual mass. You have the first ethanol-water mixture. Using the data collected here, you should be able to calculate the mole fraction of ethanol in the mixture and thus the mole fraction of water accordingly.
- Repeat step (a) through step (c) with a combination of 40 mL ethanol / 60 mL water, 60 mL ethanol / 40 mL water, 80 mL ethanol / 20 mL water, and 95 mL ethanol / 5 mL water. Record the masses you actually added in each mixing. Now you have four more ethanol-water mixtures.
- Save each of mixtures in a clean plastic bottle and tighten the cap to avoid evaporation. Label all five bottles to make sure you are able to identify their compositions. You are going to measure the physical properties of these mixtures in the next several experiments.
- You must wear your safety glasses.
- Avoid inhalation of gas vapor.