Zinc Hydroxide Formula: Definition, Preparation, Properties, Uses

Zinc Hydroxide Formula: Zinc hydroxide is an inorganic compound with the chemical formula \({\text{Zn}}{\left({{\text{OH}}} \right)_2}.\) It has the appearance of a white powder. Wulfingite, Ashoverite, and Sweetite are rare, naturally occurring zinc hydroxide minerals. Zinc hydroxide, like zinc oxide, is an amphoteric chemical. In this article, we are going to discuss more about zinc hydroxide in detail.

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Zinc Hydroxide Chemical Formula

The chemical formula of zinc hydroxide is \({\text{Zn}}{\left({{\text{OH}}} \right)_2}.\) It contains zinc \(\left({{\text{Z}}{{\text{n}}^{2 + }}} \right)\) and hydroxyl \(\left({{\text{O}}{{\text{H}}^ – }} \right)\) radicals. It is considered as an ionic compound.

Zinc hydroxide can be represented as,

The molar mass of zinc hydroxide is \(99.424\,{\text{g}}/{\text{mol}}.\)

Zinc Hydroxide Chemical Formula Derivation

The chemical formula of zinc hydroxide can be derived using the criss-cross method.

In criss-cross method, if we know the valency of the constituent elements of a compound, we can easily write its formula. The positive part’s symbol is written to the left-hand side and the negative part’s symbol to its right. The valency of each element is placed as a subscript on the side of the symbol of another element. Subscript \(1\) is not often written. Signs of the charges are discarded.

Using this, the chemical formula of zinc hydroxide can be found as,

Zinc hydroxide contains zinc \(\left({{\text{Z}}{{\text{n}}^{2 + }}} \right)\) and hydroxyl \(\left({{\text{O}}{{\text{H}}^ – }} \right)\) radicals. The valency of zinc radical is two and that of hydroxyl radical is one. By criss-crossing these valency numbers, the chemical formula of zinc hydroxide is \({\text{Zn}}{\left( {{\text{OH}}} \right)_2}.\) That is,

Study Hydrochloric Acid Formula

Preparation of Zinc Hydroxide

Zinc hydroxide can be prepared using the following methods:

Zinc hydroxide can be prepared by the reaction of zinc salts with sodium hydroxide (not in excess). That is,

1. Zinc hydroxide is precipitated when zinc sulphate is reacted with sodium hydroxide. The chemical equation for the reaction is,
\({\text{ZnS}}{{\text{O}}_4}\left({{\text{aq}}} \right) + 2{\text{NaOH}}\left({{\text{aq}}} \right) \to {\text{Zn}}{\left({{\text{OH}}} \right)_2}\left({\text{s}} \right) + {\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_4}\left({{\text{aq}}} \right)\)

2. A white colour precipitate of zinc hydroxide is formed when zinc chloride is reacted with sodium hydroxide. The chemical equation for the reaction can be given as,
\({\text{ZnC}}{{\text{l}}_2} + 2{\text{NaOH}} \to {\text{Zn}}{\left({{\text{OH}}} \right)_2} + 2{\text{NaCl}}\)

3. Zinc hydroxide is precipitated when zinc nitrate reacts with sodium hydroxide. The chemical equation for the reaction can be given as,
\(2{\text{NaOH}}\left({{\text{aq}}} \right) + {\text{Zn}}{\left( {{\text{N}}{{\text{O}}_3}} \right)_2}\left({{\text{aq}}} \right) \to {\text{Zn}}{\left({{\text{OH}}} \right)_2}\left({\text{s}} \right) + 2{\text{NaN}}{{\text{O}}_3}\left({{\text{aq}}} \right)\)

In the above reactions, if excess sodium hydroxide is added, the precipitate of zinc hydroxide formed here will dissolve in it.

Zinc hydroxide is also produced when ammonium hydroxide is added to a solution of zinc sulphate solution. The chemical equation for the reaction can be given as,
\({\text{ZnS}}{{\text{O}}_4} + 2{\text{N}}{{\text{H}}_4}{\text{OH}} \to{\text{Zn}}{\left( {{\text{OH}}} \right)_2} + {\left({{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}\)

Properties of Zinc Hydroxide  

Let us discuss the physical and chemical properties of zinc hydroxide.

Physical Properties of Zinc Hydroxide

1. Zinc hydroxide appears as a white powder.
2. Zinc hydroxide is slightly soluble in water. It is insoluble in alcohol.
3. Zinc hydroxide readily dissolves in dilute acid and alkali solutions.
4. The melting point of zinc hydroxide is approximately equal to \(398\,{\text{K}}.\) Above this temperature, it decomposes.
5. The density of solid zinc hydroxide is approximately equal to \(3.053\,{\text{g}}/{\text{c}}{{\text{m}}^3}.\)

Chemical Properties of Zinc Hydroxide

1. Zinc hydroxide is an amphoteric compound. Because of this nature, zinc hydroxide will dissolve readily in a dilute solution of a strong acid like hydrochloric acid and also in a solution of a base or alkali like sodium hydroxide.

2. Thermal Decomposition of Zinc Hydroxide

Above \(398\,{\text{K}},\) zinc hydroxide decomposes to give zinc oxide and water. The chemical equation for the reaction can be given as,

\({\text{Zn}}{\left({{\text{OH}}} \right)_2} \to {\text{ZnO}} + {{\text{H}}_2}{\text{O}}\)

3. Reactions of Zinc Hydroxide:

Different reactions of zinc hydroxide can be given as,

The reaction of Zinc Hydroxide with Hydrochloric Acid:

Zinc hydroxide reacts with hydrochloric acid to form zinc chloride and water. The chemical equation for the reaction can be given as,

\(2{\text{HCl}} + {\text{Zn}}{\left({{\text{OH}}} \right)_2} \to {\text{ZnC}}{{\text{l}}_2} + 2{{\text{H}}_2}{\text{O}}\)

The reaction of Zinc Hydroxide with Acetic Acid:

Zinc hydroxide reacts with acetic acid to form zinc acetate and water. The chemical equation for the reaction can be given as,

\({\text{Zn}}{({\text{OH}})_2} + 2{\text{C}}{{\text{H}}_3}{\text{COOH}} \to {\text{Zn}}{\left({{\text{C}}{{\text{H}}_3}{\text{COO}}} \right)_2} + 2{{\text{H}}_2}{\text{O}}\)

Reaction of Zinc Hydroxide with Phosphoric Acid:

Zinc hydroxide reacts with phosphoric acid to form zinc phosphate and water. The chemical equation for the reaction can be given as,

\(2{{\text{H}}_3}{\text{P}}{{\text{O}}_4} + 3{\text{Zn}}{\left({{\text{OH}}} \right)_2} \to 6{{\text{H}}_2}{\text{O}} + {\text{Z}}{{\text{n}}_3}{\left({{\text{P}}{{\text{O}}_4}}\right)_2}\)

In the above reactions, zinc hydroxide behaves as a base. Therefore, they are the examples of a neutralization reaction.

Reaction of Zinc Hydroxide with Sodium Hydroxide:

Zinc hydroxide reacts with sodium hydroxide to form sodium zincate (which will dissolve in it to form a coloulress solution) and water as the products. The chemical equation for the reaction can be given as,

\({\rm{Zn}}{\left( {{\rm{OH}}} \right)_2}\left( {\rm{s}} \right) + 2{\rm{NaOH}}\left( {{\rm{aq}}} \right) \to \mathop {{\rm{N}}{{\rm{a}}_2}{\rm{Zn}}{{\rm{O}}_2}\left( {{\rm{aq}}} \right)}\limits_{{\rm{Colourless}}\,\,{\mkern 1mu} {\rm{solution}}}  + {{\rm{H}}_2}{\rm{O}}\left( {\rm{l}} \right)\)

Uses of Zinc Hydroxide

1. In surgical dressings, zinc hydroxide is used as an adsorbent.
2. Zinc hydroxide is also used to find zinc salts by mixing sodium hydroxide with the suspect salt.
3. Zinc hydroxide is used as a filler for paints, textiles, plastics, etc.
4. It is used as an insulating material to protect from noise, cold, etc.
5. It is used for the production of cement or food, air or spacecraft machinery, electrical machinery, etc.
6. Zinc hydroxide is used for the manufacturing of plastics, plastic additives, etc.
7. Zinc hydroxide is used as an adsorbing agent in medicine.
8. Zinc hydroxide, in combination with zinc oxide is widely used in calamine creams, ointments, baby powder, skin lotions, and cosmetics.

FAQs on Zinc Hydroxide

Q.1. What is the formula of zinc hydroxide?
Ans: Zinc hydroxide is an inorganic compound with the chemical formula \({\text{Zn}}{\left({{\text{OH}}} \right)_2}.\) It is an ionic compound.

Q.2. What is zinc hydroxide used for?
Ans: Zinc hydroxide has several uses. In surgical dressings, zinc hydroxide is used as an adsorbent, used to find zinc salts by mixing sodium hydroxide with the suspect salt, used as a filler for paints, textiles, plastics, etc.

Q.3. What is the name of \({\text{Zn}}{\left({{\text{OH}}} \right)_2}\)?
Ans: The chemical name of \({\text{Zn}}{\left({{\text{OH}}} \right)_2}\) is zinc hydroxide. It is an amphoteric compound.

Q.4. Is zinc hydroxide poisonous?
Ans: Zinc hydroxide is not for its acute toxicity. However, its direct contact can cause skin and eye irritation. It is very toxic to aquatic life.

Q.5. Is zinc hydroxide an acidic salt?
Ans: No, zinc hydroxide is not an acidic salt. It is an amphoteric substance. That is, it can act either as an acid or a base.

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