Figure 1-86. Reaction of aluminum metal with NaOH in water. Experiment 10. Reaction of Aluminum with NaOH.
If you decide not to do the experiments, still read this subsection.
For this experiment, you will need aluminum foil and sodium hydroxide, NaOH. Aluminum foil is available from food and other stores. Sodium hydroxide (lye) is the sole or main component of solid drain openers sold in hardware stores. Food grade NaOH is available from a number of online vendors. Buy the smallest possible quantity of NaOH.
Let us now refresh our memory on NaOH and the reaction (Figure 1-86) in order to come up with safety measures
for carrying out the experiment.
1. You should always remember that NaOH is a very caustic material that is hazardous to the skin and especially to the eyes. Therefore, direct contact with solid NaOH and its solutions must be avoided. Wear gloves and safety glasses when doing the experiment. If NaOH makes contact with your skin, immediately rinse the area with tap water until the slippery feel has subsided or gone altogether. Immediately after that rinse the affected area with a small amount of white vinegar and then water again. Why vinegar? Because vinegar is a weak solution of acetic acid that will neutralize the residual NaOH.
2. As NaOH dissolves in water, much heat is released. The reaction (Figure 1-86) is also exothermic. Consequently, the solution will get quite warm or even hot during the experiment. Be careful touching the reaction vessel.
3. The reaction produces H2
(Figure 1-86). Since hydrogen is flammable, there should be no open flame sources in the vicinity of the reaction. It is best to perform the experiment outdoors.
Place 5-10 aluminum foil strips at the bottom of a glass. The strips can be roughly a square inch in size. Pour tap water onto the strips until the glass is approximately one-quarter full. Using a teaspoon, pincer or forceps, add a few pellets of NaOH and gently swirl the contents of the glass. Observe the formation of bubbles of pure hydrogen formed in the reaction (Figure 1-86). After the hydrogen evolution has ceased, add vinegar to fill up the glass. Vinegar will neutralize the remaining NaOH (if any left) within the time of mixing, after which the mixture can be safely disposed of.
Watch this video
showing two guys having lots of fun with the reaction between aluminum and NaOH. I discourage you from running this reaction on a large scale. First, you do not want a spillover of a hot caustic solution that can ruin your countertop and household goods and, even worse, damage your skin. Second, you should avoid evolution of large quantities of flammable hydrogen. Third, if run on a large scale, the reaction generates a lot of heat, which poses the risk of thermal burns.
Now take another look at the chemical equation of the reaction of aluminum with sodium hydroxide (Figure 1-86). Like the previously presented formula of sodium zincate (Na2
), that of sodium aluminate (NaAlO2
) is simplified. An overly picky chemist might even blame me for teaching you incorrect formulas. However, I do this on purpose, in order to avoid oversaturating you with information that I believe is not only unnecessary for the learning process at this point, but could have a distracting and confusing effect. If you want to know the correct formulas right now anyway, here they are: Na2
] and Na[Al(OH)4
]. They might look strange to you. How can Zn and Al be tetravalent? What are these square brackets in the formulas and why do we use them? Well, these substances are so-called coordination compounds
, also known as metal complexes or "ate"
complexes. Chances are that at this point you do not have enough knowledge of basic chemistry to study coordination compounds. One step at a time, so let us first learn and understand simpler things in chemistry. 1.17.4. Exercises.
1. Both NaOH and KOH occur in nature in the form of crystalline minerals. True or false? Answer
2. Calcium hydroxide is called slacked lime, made by the reaction of quicklime (CaO) with water, and used in large quantities to make concrete. True or false? Answer
3. Finish and balance the following chemical equations.
(a) NaOH + HNO3
(b) KOH + CuCl2
+ HCl =
+ 3 NaOH =
+ NaOH (excess) =
+ KOH =
+ NaOH =
O + H2
O = Answer