You have been given five vials, labeled #1-5. These vials contain methanol, 2-propanol, acetone, hex — Intermolecular Forces and Liquids Chemistry Question
Problem Context
You have been given five vials, labeled #1-5. These vials contain methanol, 2-propanol, acetone, hexane and water (though not necessarily in this order). You have also been given a container of table sugar (C12H22O11).
Design and carry out an experiment to determine which liquid is in each labeled vial. You have access to a clock or timer.
Model Answer
This problem asks students to distinguish 5 different liquids.
Observations and data can be used to identify each liquid by observing:
1. Relative viscosity 2. Miscibility 3. Evaporation rates 4. Solubility with the provided sucrose sample 5. Rates of solubility with sucrose 6. Odor 7. Densities
Excellent answers for this problem included at least three of these observations in chart or table form as part of their plan. In the data/observations, we looked for quantitative data (time for evaporation, time for completely dissolved sugar samples using set volumes of each liquid and set masses of sugar samples, etc.). Credit was given for multiple trials with quantitative data and for complete observations with all five samples. Conclusions included correct identification of each of the five liquids using more than one observation for each as evidence for student results. The best student answers were organized, provided observations in chart or tabulated form, and had a high degree of specificity with units were included for quantitative data.
Sample data:
A single drop of each liquid was placed on a watch glass and the time was recorded it took for that drop to completely evaporate:
Vial liquid evaporation time (one drop) in min. (at room temp.)
#1 2-propanol 2:15
#2 Water still there
#3 Methanol 1:05
#4 Hexane 0:30
#5 acetone 0:20
These data correspond nicely to predictions based on the degree of hydrogen bonding and relative intermolecular forces of attractions between molecules of each of the samples present.
Solubility with sucrose:
Vial #2 dissolved the sugar easiest and quickest and in the greatest amount, evidence that #2 was water; #1 and #3 slightly; #4 and #5 less so. Excellent student answers showed experiments with consistent amounts of sugar and volumes of each vial used with recorded times for completely dissolved sugar observed.
Miscibility:
Vial #4 was immiscible with #2, forming two distinct layers, conclusive evidence that #4 was hexane on the top layer, water on the bottom layer. Vials #1, 2, 3 were miscible with one another; #4 slightly with #5.
Odors:
For excellent data, students might have noted that #2 had no apparent odor, #1, 3 had an ‘alcohol-like’ smell, or even ‘smells like rubbing alcohol (#1), that #4 smelled like ‘gasoline’, or that #5 had a ‘nail polish-like’ smell.