Zinc hydroxide: amphoterism, preparation, applications

Zinc hydroxide – summary formula, properties

What is zinc hydroxide? The structural formula of this compound indicates that it is built of a positive ion in the form of a metal (zinc) and contains negative ions and hydroxyl groups. This composition also describes the formula of the hydroxide: Zn(OH)₂.

What are the characteristics of zinc hydroxide? The molecular weight of Zn(OH)₂ is 99.39 ± 0.02 g/mol. It is:

• an odourless, hygroscopic solid with a loose consistency,
• slightly soluble in water (when we combine zinc hydroxide with water, the precipitates at the bottom of the vessel will turn white and thicken).

Zinc hydroxide powder is white or off-white in colour (the colour of zinc hydroxide may also resemble a shade of off-white, or a light grey).

There is one more feature typical of zinc hydroxide – the structure of this compound resembles diamond-shaped crystals (rhombohedrons).

Zinc hydroxide: obtaining it

How is zinc hydroxide formed? Chemists call the reaction of obtaining Zn(OH)₂ a precipitation reaction, because thanks to the precipitation reaction the product obtained is in the form of a precipitate. What is needed to produce zinc hydroxide? How is this precipitate obtained? All one needs to do is to combine a small amount of sodium hydroxide solution (one can also use potassium hydroxide as a substitute) with a solution containing zinc salts.

Is zinc hydroxide amphoteric?

Amphoterism means that chemical compounds react as an acid or as a base depending on what substances they are combined with. This property is exhibited by zinc hydroxide. The chemical nature of Zn(OH)₂ can be described as amphoteric because it behaves like an acid or a base in various configurations.

How to check if zinc hydroxide is amphoteric? When we combine it with a strong base, it will behave like an acid – and vice versa: when combined with strong acids, it will react like an alkaline compound. No wonder that amphoteric zinc hydroxide has found various applications in industry and in everyday life.

Zinc hydroxide – applications

What is zinc hydroxide useful for in everyday life? A solution of this compound or a powdered form of Zn(OH)₂ can be used for the production of zinc salts, for example. These salts have a cleansing, antibacterial, and regenerating effect. Therefore, zinc hydroxide in cosmetics industry works indirectly as a raw material, thanks to which various types of body care products are made. These include, for example:

• face wash liquids,
• shower gels,
• intimate hygiene products,
• anti-dandruff shampoos and rinses, shampoos for daily hair care,
• soaps and washing foams,
• preparations and cosmetics for normal and acne skin (creams, ointments, serums).

The amphoteric and hygroscopic properties of zinc hydroxide are also highly valued in medicine and in the treatment of extensive injuries. It is a high-quality adsorbent, that is to say, a substance that perfectly absorbs and thickens other substances (e.g., human blood). Bandages containing a hydroxide filler work well, for example, after surgical procedures that result in heavy bleeding. Surgical adsorbents protect the wound, which can then heal quickly and without complications.