Academic journal article The American Biology Teacher

Using the Boiling Point of Water to Learn about Hydrogen Bonds

Academic journal article The American Biology Teacher

Using the Boiling Point of Water to Learn about Hydrogen Bonds

Article excerpt

The boiling point of water can be used to illustrate the importance of hydrogen bonds in living systems. The boiling point of a compound is the temperature at which a liquid becomes a gas. All other things being equal, the boiling point should be approximately proportional to molecular weight, since molecules are held together by weak forces that are roughly proportional to mass. When the temperature is high enough to separate the individual molecules from each other, they boil, or become a gas.

I give students the following chart:

Molecular Weight    Substance    Boiling Point

       2            [H.sub.2]
      18            [H.sub.2]O
      28            [N.sub.2]
      32            [O.sub.2]
      44            C[O.sub.2]

I then fill in the boiling points as follows. I round to the nearest whole number, but here I give the actual numbers for reference. Absolute zero is -273[degrees]C, or 0[degrees]Kelvin.

[H.sub.2] = -252.87[degrees]C

[N. …

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