MadSci Network: Chemistry

Re: Why does liquid collect together in 'puddles'?

Area: Chemistry
Posted By: Henry Boyter, Senior Scientist
Date: Sat Sep 27 23:27:02 1997
Area of science: Chemistry
ID: 874338217.Ch

There are two main factors that determine what a liquid will do when placed on a surface. The first is of course gravity which tends to make the liquid spread out. The second is the attraction of the molecules for each other. In water, these forces are given by the hydrogen bonding and the surface tension of and in the water droplets. These forces tend to make the water molecules stick together. When these forces are great as in water, they may be greater than the gravity component and thus droplets are formed.

Anything that can disrupt these forces will cause the water to spread out. These can be mechanical forces or chemical forces. Mechanical forces can be actions such as stirring the droplet or placing an object on the droplet. Also, mixing the water with other chemicals can disrupt these forces. Try this: mix water with salt, sugar, alcohol, cooking oil, or other household chemicals and see if the droplets differ. Try dilute and concentrated solutions. Then try the liquids themselves. Cooking oil which has little attractive forces will spread out more than water. Alcohol should be between water and cooking oil.

Remember!!!! All experiments must be done under adult supervision!!!!!

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