Volume Reduction During Mixing of Ethanol and Water

A well known experiment on volume reduction of ethanol mixed with water is microscaled.  Using a capillary the volume change can clearly be observed or even measured when only 2 mL of each two liquids are mixed.

Materials
Three test tubes (12 mm x 75 mm), test tube stand, small piece of glass or a glass grain, rubber stopper that fits on the test tube, capillary, three plastic pipettes, latex glove.

Chemicals
Ethanol, paraffin oil, distilled water, food dye.

Experimental

• Transfer 2 mL water into one test tube and 2 mL ethanol into the other one.
• Add some food dye and mix.
• With a pipette put appoximately 2 mL of the coloured water in a third test tube,
• Add a piece of glass.
• With another pipette add few drops of paraffin oil. It will separate the water from the ethanol.
• Than, carefully add about 2 mL of coloured ethanol with a dry pipette. Try to preserve the layers.

Fig. 1 Volume reduction in a capillary during mixing ethanol and water 
a) Ethanol and water before mixing    b) Height of ethanol in the capillary
c) Mixing ethanol and water                d) Height in the capillary after mixing.

• Hold the test tube with two fingers at the upper part and close it with a rubber stopper that has a capillary as shown on Fig. 1a.
• By pressing the stopper provide the capillary with a high level of coloured ethanol.
• Cut a glove and put a piece on the forefinger.
• Invite the students to watch and before mixing mark the level of ethanol (Fig. 1b).
• Close the upper hole of the capillary with the forefinger and mix the water and the ethanol by tilting twice the test tube for more than 90º (Fig. 1c).
• After that ask for attention on the capillary and remove your finger.
• Mark the new level (Fig. 1d). For quantitative evaluation measure the inner diameter of the capillary and calculate the difference of the two volumes.

Observation and discussion
 Due to the small diameter of the capillary a spectacular volume reduction is visualized with a small quantity of the two liquids. 
The volume reduction is a result of a re-arrangement of the two different kinds of molecules and their hydrogen bonding. In other words, molecules of water and of ethanol are packed in a certain way, and upon mixing they are repacked and the experiment shows that these molecules are much better packed when they are together in mixture.
Notes                                                 
The glass piece is used to provide better mixing and the food colours are applied to make this phenomenon more vivid. Do not hold the test tube at the lower part. That will result in heating the system and changes in the hight of liquid in the capilary.