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What happens to alkali metals in water and why?
All alkali metals are combustible in water to a certain extent. Lithium (the least reactive) is burns quickly in water. The reaction is neither explosive or dangerous if done properly. As you move down the alkali metal column on the periodic table the elements have a much stronger reaction with water. So as we move down the list sodium is next. Sodium as a slightly more interesting reaction with water as it tends to spiral around the beaker of water as it burns a bright red. Potassium reacts more dangerously and usually burns with a light purple flame. Now rubidium and caesium have reactions that anyone can appreciate. Rb sinks in water whereas the three before it float along the top of the water. After it sinks it then explodes producing a shock wave which can shatter the container it is in. Cs has a similar reaction with water but on a larger scale, causing a much larger explosion. Information on francium is still hard to come by but I am sure it must have been tested in water many times given that the other alkali metal produced such interesting reactions. Answering why these chemicals react like this has been a bit harder but this is what I have found out so far. When an alkali metal reacts with water it produces an alkali hydroxide and hydrogen gas. During this reaction a massive amount of heat is released which combusts with the hydrogen gas causing the combustion of the entire alkali metal.
A knowledge of chemistry is important in the situation foremost because without it these reactions could be highly dangerous. Chemistry is also important with these chemicals because with a knowledge of chemistry these reactions could be put into great applications. Although after hours of searching I have not been able to find a direct application for alkali metal's highly explosive nature, the products of their reactions have numerous applications. For example, Lithium hydroxide is used as an air purifier, a lubricant, a catalyst and much more. Potassium hydroxide is used for a much wider variety of things than lithium hydroxide however not as many things as sodium hydroxide which is used in analytical chemistry, soap making, paper production, biodiesel fuels, cleaners, drugs, and that is just the beginning. These things could not have been made or discovered without a knowledge of chemistry. So I think the second reason chem is important here is for exploration and discovery...and we all know how chemists love that.
Mini Bibliography
"Group one: The Alkali Metals." Chemsoc. 28 Jan 2008 <http://www.chemsoc.org/viselements/pages/data/intro_groupi_data.html>.
"Sodium hydroxide." 2008. Wikipedia, The Free Encyclopedia. 28 Jan 2008 <http://en.wikipedia.org/w/index.php?title=Sodium_hydroxide&oldid=186158691>.
"Lithium." 2008. Wikipedia, The Free Encyclopedia. 28 Jan 2008 <http://en.wikipedia.org/w/index.php?title=Lithium&oldid=187460066>.
2 comments:
good article on combustion of alkali metals in water. i like how you organized your information so that it was presented like we were going down the periodic table. How cool would that be if we could combust rubidium in class?
Snazzy write up about the combustion of alkali metals in water; it all sounds very cool / fun. For not finding a reaction of francium: francium is one of the most rare elements in the world, with "as little as 30 g (one ounce) exist[ing] at any given time throughout the Earth's crust." (wikipedia). I assume that not much information exists on the subject because many experiments have been carried out, but it is still surprising that no information at all would be readily available. But based on your posts, it is not hard to guess the direction of the results of the experiment.
I agree with Zach; let's ask JV if we can combust alkali metals in chem class :D
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