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Name:  Dustin
Status: other
Grade: other
Location:N/A
Country: N/A
Date: 12/14/2005


Question:
Hello, I am currently taking grade 11 chemistry and doing rather well in the class. I have ambitions to enter the field of chemistry when I am older and finished University. Now lets get down to business.

I have recently found out that adding a piece of Al to a solution of KOH causes a reaction in which hydrogen is produced. This particular reaction confuses me because I do not not know how an element with a reactivity such as Al is displacing hydrogen. What I am asking for is a simple chemical equation for this reaction because I am having trouble coming up with my own.


Replies:
Dustin,

The equation that you are looking for is:

2Al(solid) + 6H2O + 2KOH ---> 2K[Al(OH)4] + 3H2 (gas)

This is typically an intermediate step in the production of alum by further addition of sulfuric acid.

Hope this helps.

Bob Hartwell


This is a famous reaction. Aluminum is so reactive, so energetic, it is the most common metal added to rocket fuel. It would always react with water, if it did not tend to grow an oxide film that blocks off the surface and stops the reaction. Aluminum oxides are soluble in basic water solutions, so KOH enables the reaction to go continuously.

Basically, it is:

2 Al(0)+ 6 H2O --(KOH)--> 2 Al(+3) + 6 OH(-) + 3 H2

There are many slightly different ways to express it which more nearly describe the exact state of the stuff in water after the reaction. This is where the KOH gets involved a little, and where one might understand why precipitates form.

2 Al(0) + 6 H2O + 2 K(+) + 2 OH(-) --> --> K2Al2O4.3H20 + 3 H2 + OH(-)

or 2 K+ + 2 (Al(OH)4)- + 3 H2O + + 3 H2 + OH(-)

or a mix of these and similar things.

This reaction consumes some OH- as well as Al and water. I would not assume that K2Al2O4.3H20 is exactly what is there, but at least the equation is balanced.

The hydrogen evolved is flammable and explosive. Please only do this with supervision and use no glass containers. Use ventilation. The alkaline water-mist is bad for lungs eyes and skin, too.

Jim Swenson



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