How does heating a solvent, crushing a solute, or stirring
a mixture aid the reaction of Alka-Seltzer?
What you need
A few packages of Alka-Seltzer
One hot plate or stove-top
Stove pan to heat water in
Two or three glass beakers or pots
Water (some hot using the hot plate and some cold, using ice cubes or cooling it down in a refrigerator)
Stopwatch or clock
What you do
Place some cold water in a beaker or pot. Add one tablet of
the Alka-Seltzer. Time how long it takes for the Alka-Seltzer
tablet to dissolve completely in the water. Now try the same experiement
using hot water. Compare the times. Finally, try crushing the
tablet and adding it to a new beaker of hot water. Is the time
any different now?
What's going on here
The tablet of Alka-Seltzer reacts in water by fizzing and foaming until the tablet is gone. Essentially, carbon dioxide gas is produced in this reaction. You might have noticed that the tablet reacted very slowly in the cold water, quite a bit faster in the hot water, and much, much faster when the tablet was crushed. Let's think about some reasons why this might happen. In hot water, the water molecules are moving around very fast compared to the cold water. Since they are moving around very fast, more molecules are able to bump into the tablet in hot water than in cold water. Every bump of a water molecule causes a reaction to occur. So, if the molecules are bumping into the tablet more frequently, the tablet will dissolve quicker. If you're fuzzy on this topic, read up a bit on temperature.
Why should the crushed tablet dissolve faster than a regular tablet? Well, think of it this way. If you were trying to catch a mouse in your basement, would you rather have ten people, lined up single file, walk straight up to the mouse, one after the other? Or, instead, would you rather form a circle around the mouse with those ten people? You probably would say form a circle. Why is this more effective? By surrounding the mouse, you are covering more areas where the mouse can escape. If you approach the mouse from only one direction, it can escape in many other directions. The same principle governs dissolving tablets. When you crush a tablet, you expose new surfaces that were originally on the inside of the tablet. These surfaces can react with water. With a greater number of surfaces, the water is able to surround more and more of the tiny pieces of the tablet, dissolving it faster. Check out this link on surface area.
Also, check out Alka-Seltzer's website at http://www.alkaseltzer.com/home/default.htm for more details, more science experiments, and information regarding the chemistry behind Alka-Seltzer.
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