Structure of Vodka

Vodka is a colourless, tasteless solution sold as an 80-proof beverage, which means it is a solution of 40% ethanol (ethyl alcohol) and 60% water. There are many different brands of Vodka at different prices, and people claim to be able to "taste" the difference. Scientists at the University of Cincinnati and the Moscow State University have been studying this phenomenon.

Dmitri Mendeleev, a Russian Chemist famous for his work on the Periodic Table, believed that a solution of 40% ethanol and 60% water would form peculiar clusters of molecules called hydrates.

Linus Pauling, a Nobel Prize winning Chemist, thought the hydrate clusters might consist of an ethanol molecule surrounded by a framework of hydrogen-bonded water molecules.

The scientists from the the Universities of Cincinnati and Moscow State analyzed the composition of 5 popular Vodka brands and found that they differed in their concentrations of ethanol hydrates. When people express a preference for one Vodka brand over another, it is not a question of "tasting" different, they appear to be perceiving the internal structure of the Vodka. Vodkas with a low concentration of ethanol hydrates might be perceived by drinkers as watery.

Reference:
Naiping Hu, Dan Wu, Kelly Cross, Sergey Burikov, Tatiana Dolenko, Svetlana Patsaeva, Dale W. Schaefer. Structurability: A Collective Measure of the Structural Differences in Vodkas. Journal of Agricultural and Food Chemistry, 2010; DOI: 10.1021/jf100609c

Study Questions:

• The concentration of beverages containing ethanol, such as spirits, are often labelled as "proof", eg, 100 proof, 80 proof. What other ways are there to express the concentration of solutions?

• Convert 80 proof to its equivalent for each of the different concentration measures you listed above.

• For the ethanol molecule, write

1. the structural formala
2. the condensed structural formula
3. molecular formula
4. empirical formula

• What is hydrogen bonding?
• Draw a diagram showing how water molecules can hydrogen bond to each other.
  

• Draw a diagram to represent an ethanol molecule surrounded by 5 hydrogen-bonded water molecules.
• At high alcohol concentration, clusters of ethanol molecules appear. What could hold these ethanol molecules together in a cage-like structure?