Conclusion

We spent several weeks creating reactions of Alkali Earth metals with water.  To see how we did this, visit our Methods page.  We determined several interesting conclusions from the experiments we did.  

After talking with Mr. Roser on the chemistry floor, we were able to get some valuable information about our observations of the reaction.  First, one may notice that the metals do not seem to go below the water's surface.  This is easily explained by the fact that all of the alkali metals are less dense than water and are therefore able to float.  Also, hydrogen produced in the reaction buoyed the metals at the water's surface, causing the metal to skid on the top of the water similarly to a puck on an air hockey table.

The second conclusion we reached was that the metal appears to be initially propelled by hydrogen gas, a product in each of the reactions.  We can not predict which direction the metal will go in initially because the atoms react in a completely random order therefore projecting it in a random direction.  After it has been propelled in one direction the area of low pressure created behind the metal, which becomes a place where the metal and the water can react more readily.  Because there is more of the reaction taking place in this one area, producing more hydrogen gas on one side of the metal it is continually propelled in the direction it initially started in until it hits the sides of the beaker.  We will still have some variability due to the changing mass of the water and friction caused by the water.

Finally,  the spherical shape observed in the sodium and potassium reactions is due to the melting of the metals.  During the reaction temperatures greater than the melting points of both sodium and potassium are reached.  Once the melting point of the metal has been reached it changes from its solid form to a liquid.  Because the liquid metal's most stable shape in water is that of a sphere it will change from it's original shape.  Although it may be seen changing shapes slightly from it's sphere shape to oblong it will always go back to it's most stable shape until the reaction is complete.  Lithium could also be observed to do this if a big enough piece was dropped in.  A bigger piece would allow the reaction to take place longer thus giving it more time to generate the heat needed to reach lithium's melting point.

Bibliography:

CRC Handbook of Chemistry and Physics.  Ed.  Robert C. Weast, Ph.D.  The Chemical Rubber Co. Cleveland, Ohio: 1962.

http://www.webelements.com/webelements/index.html

Special thanks to Dr. Winters, Mr. Roser, Dr. Sturgeon, Dr. Bennett, Tim Reibold, Brandon Winterling, and Dahl Clark.