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37555A Chemistry Lesson (was) Re: Product Dilution Chart

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  • Harry
    Nov 6, 2006

      --- In Distillers@yahoogroups.com, "rodmacd2000" <rmacdoug@...> wrote:
      > Thanks Harry. This table (assuming it's correct) explains why I've
      > always ended with higher proof booze then desired when diluting in the
      > straightforward manner.
      > The table requires adding a fair bit more water than you'd expect. For
      > example if you want to dilute 100 units of 95% abv to 40% abv the
      > simple calculation requires mixing with 137.5 units of water. The
      > table says to add 144 units of water - a difference of almost 5%.
      > This is not at all trivial and no doubt reflects the infamous
      > "shrinkage" phenomena. I expect that the definite heating effect that
      > we see during dilution is also caused by this "shrinkage".
      > I'm curious about this thing, having slept thru most of the Chemistry
      > classes I attended about a century ago. I assume it is not a classical
      > chemical reaction. Maybe a kin to the equally curious phenommena of
      > Azeotrope formation?
      > Rod


      Hi Rod,

      Yes it is a classical chemical reaction.  It's called an "Exothermic Reaction", and you're right that it has to do with the "shrinkage".  It's all about "Hydrogen Bonding".  Rather than try to explain it myself, I've borrowed an experiment from a high school Chem class (source given).  It will explain things very nicely, and you can have a bit of fun in the process.


      Water and Alcohol Mixtures and "The Amazing Air Bubble"

      Chemical Topics or Concepts: -

      • Observation skills
      • Prediction and Problem Solving
      • Solutions and Solubility, miscibility
      • Density
      • Hydrogen Bonding
      • Vapor pressures

      Materials: -

      • Test tubes - classroom quantity
      • Corks to fit the holes in the test tubes.
      • Yellow and Blue food coloring
      • Ethanol or Methanol
      • 20-30 thin stem pipettes

      Set-up Procedure:

      1. Make about 1 liter of water solution by adding 10 –15 drops of yellow food coloring.
      2. Make about 1 liter of alcohol solution by adding 10-15 drops of blue food coloring.
      3. Place half of the pipettes into the water solution and the other half into the alcohol solution.
      4. Place the test tubes with corks in an easily accessible place for the students.

      Student Instructions:

      1. Goal:To place an equal amount of yellow and blue liquid into the same test tube, with no air bubbles in the test tube and keeping the liquids the same color. Place both the yellow and blue liquid into the test tubes. The only requirements are that you must fill the tube completely full so that when you put the cork into the test tube there is no air bubble, and that you use ½ blue liquid and ½ yellow liquid.
      2. Repeat the procedure as many times as you like and be ready to share your observations in about 15 minutes.


      1. When alcohol and water mix the resulting volume of the two solutions is less than the total of the individual volumes. In this case "one plus one" does not equal two. The reason for this decrease in volume can be attributed to the hydrogen bonds which develop between the alcohol molecules and the water molecules (See "Surface Tension of Water" to see a further explanation of hydrogen bonding). This hydrogen bond pulls the molecules really close to each other and the small water molecules will fit nicely in the spaces between the alcohol molecules.

      2. If students added the blue (alcohol) liquid to their test tube first and then added the yellow (water) to that test tube, they would find immediately that the color turns green as the heavier (more dense) yellow water sinks to the bottom and "dissolves" into the alcohol on the way down, making the solution green.

      3. If the students added the yellow (water) liquid first and then placed the blue (alcohol) liquid on second, they should observe that two distinct layers are formed. The more dense yellow water solution will stay on the bottom and the blue alcohol mixture will "float" on top of the water.

      4. If the students have the blue on bottom and the yellow on top, have them invert the test tube. What they will notice is that the color changes to green and that the test tube warms up and that an "air" bubble appears. This bubble is a result of the volume decrease when two liquids mix. What is the composition of that "air" bubble? The "air" bubble is probably very little "air". Initially, it is a vacuum, due to the liquid molecules coming closer together when they dissolved, but for the most part, once the liquids have mixed, the "air" bubble is water and alcohol vapor. (See "Boiling Water in a Syringe" for an explanation of vapor pressure). Every liquid "loses" some of its molecules to the vapor state, even at room temperature. Alcohol "loses" its liquid molecules to the vapor state much more quickly than water does. This "air" bubble is primarily alcohol and water molecules which have "escaped" to the vapor state.

      5. The warming of the test tube indicates that the process of mixing alcohol and water is an exothermic reaction. As the molecules come closer together and form hydrogen bonds, they release extra energy that is released in the form of heat energy.

      Reference: Woodrow Wilson Conference. Grandvalley State University. Allendale, MI: 1996.

      [Source: Covenant Christian High School.  http://www.iserv.net/~chargers/chem/seccwatalcohol.htm ]



      regards Harry

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