Aluminum Hydroxide: Formula & Side Effects

Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

Have you ever had really bad heartburn or a sour stomach? If so, aluminum hydroxide can be used to treat it. Continue reading to learn about aluminum hydroxide and its formula. Understand the side effects from taking medications containing this compound.

Aluminum Hydroxide: An Overview

I'm sure we've all been there. You decide to eat that spicy burrito only to feel the effects of heartburn shortly after. Rather than fighting through the pain, you run to the pharmacy and grab a bottle of antacid. But do you know the ingredients in that bottle that work to help relieve your heartburn? One is called aluminum hydroxide.

Aluminum hydroxide is a chemical compound with the molecular formula Al(OH)3. As a mineral, it is naturally found as the ore called gibbsite. The molecular weight of aluminum hydroxide is 78.0 g/mol. The color of aluminum hydroxide, as a solid substance, is white. Its density is 2.42 g/cm3. In addition to these properties, there are two unique properties of this compound: amphoterism and polymorphism.

The mineral ore gibbsite where aluminum hydroxide is naturally found

Amphoterism relates to a substance that can react as either an acid or base. For example, the hydroxide (OH) in aluminum hydroxide can act as weak base when reacting with the strong acid, hydrochloric acid (HCl). A weak base is a base that partially dissociates or breaks apart in solution. On the flip side, the hydroxide in aluminum hydroxide can also act as a weak acid when reacting with the strong base, sodium hydroxide (NaOH). A weak acid is an acid that partially dissociates or breaks apart in solution. The ability to act and take on the properties of either a weak acid or base classifies aluminum hydroxide as amphoteric.

Examples of aluminum hydroxide as an amphoteric substance: (a) with HCl and (b) NaOH

Besides amphoterism, aluminum hydroxide is also polymorphic. Derived from the Greek meaning, 'having multiple forms,' polymorphism refers to the ability for a solid material to have multiple forms or crystal structures. Aluminum hydroxide has four different forms: gibbsite, bayerite, nordstrandite, and doyleite.

Uses of Aluminum Hydroxide

Aluminum hydroxide has medicinal purposes. As we briefly discussed at the beginning of this lesson, aluminum hydroxide is an added ingredient in antacid medication. Hence, it is effective at treating illnesses such as acid indigestion, upset stomachs, and heartburn.

Aluminum hydroxide can also be used in the manufacturing industry for several purposes, such as the waterproofing of fabrics and the production of pottery. Did you know your favorite antiperspirant might contain a derivative of aluminum hydroxide? It most certainly does. In fact, that derivative is a close cousin of aluminum hydroxide called aluminum hydroxychloride. When used in antiperspirants it can act as an astringent, clogging pores to prevent sweat or perspiration from occurring.

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