Zinc hydroxide, chemically represented as Zn(OH)₂, is an inorganic compound that plays an essential role in chemistry, industry, and medicine. One of the fundamental properties of any compound is its molar mass, which is crucial for calculations in stoichiometry, chemical reactions, and industrial applications.
This topic explores the molar mass of Zn(OH)₂, how to calculate it, and its chemical properties, solubility, and uses.
Molar Mass of Zn(OH)₂
What is Molar Mass?
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is calculated by summing up the atomic masses of all the elements present in a compound.
Step-by-Step Calculation of Zn(OH)₂ Molar Mass
The molecular formula of zinc hydroxide is Zn(OH)₂, which contains:
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1 Zinc (Zn) atom
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2 Oxygen (O) atoms
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2 Hydrogen (H) atoms
Now, using the atomic masses of these elements:
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Zinc (Zn) = 65.38 g/mol
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Oxygen (O) = 16.00 g/mol
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Hydrogen (H) = 1.008 g/mol
The molar mass is calculated as:
Thus, the molar mass of Zn(OH)₂ is 99.39 g/mol.
Properties of Zinc Hydroxide
Zinc hydroxide exhibits both physical and chemical properties that make it useful in various fields.
Physical Properties
| Property | Description |
|---|---|
| Molecular Formula | Zn(OH)₂ |
| Molar Mass | 99.39 g/mol |
| Appearance | White, gelatinous or powdery solid |
| Density | 3.05 g/cm³ |
| Solubility in Water | Slightly soluble |
| Melting Point | Decomposes before melting |
Chemical Properties
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Amphoteric Nature: Zn(OH)₂ reacts with both acids and bases.
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Decomposition: When heated, it decomposes into zinc oxide (ZnO) and water.
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Precipitation: It forms as a white precipitate when a base is added to a zinc salt solution.
Solubility and Amphoteric Behavior of Zn(OH)₂
Is Zn(OH)₂ Soluble in Water?
Zinc hydroxide is sparingly soluble in water, meaning it does not dissolve easily. However, it dissolves in both acidic and basic solutions, showing its amphoteric nature.
Reaction with Acids
In an acidic solution, Zn(OH)₂ dissolves to form zinc salts:
This reaction produces zinc chloride (ZnCl₂), which is highly soluble in water.
Reaction with Bases
Zn(OH)₂ also dissolves in strong bases, forming soluble zincates:
This reaction results in sodium zincate (Na₂ZnO₂), a soluble complex ion.
How is Zinc Hydroxide Prepared?
Zinc hydroxide can be obtained through precipitation reactions from zinc salts and bases.
1. Precipitation from Zinc Salts
Adding a strong base (such as NaOH or NH₄OH) to a zinc salt solution results in the formation of Zn(OH)₂ as a white precipitate:
2. Formation from Zinc Oxide
Zn(OH)₂ can also form by reacting zinc oxide (ZnO) with water in a weak acid:
Industrial and Commercial Applications of Zn(OH)₂
1. Pharmaceuticals and Medicine
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Used in antiseptic creams and lotions for treating skin conditions.
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Found in calamine lotion, which relieves itching and rashes.
2. Chemical and Laboratory Uses
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Acts as a precursor for zinc oxide (ZnO).
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Used in chemical analysis to detect metal ions.
3. Paints and Coatings
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Used as an anti-corrosion coating for metals.
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Helps in the production of high-performance paints.
4. Polymer and Rubber Industry
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Enhances heat resistance in rubber products.
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Acts as a stabilizer in plastic manufacturing.
5. Environmental and Water Treatment
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Helps remove heavy metals from wastewater.
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Used in industrial effluent treatment.
Comparison of Zn(OH)₂ with Other Hydroxides
| Compound | Formula | Molar Mass (g/mol) | Solubility in Water | Amphoteric | Common Use |
|---|---|---|---|---|---|
| Zinc Hydroxide | Zn(OH)₂ | 99.39 | Slightly Soluble | Yes | Medicine, coatings, water treatment |
| Calcium Hydroxide | Ca(OH)₂ | 74.09 | Moderately Soluble | No | Cement, agriculture |
| Magnesium Hydroxide | Mg(OH)₂ | 58.32 | Slightly Soluble | No | Antacids, fire retardants |
| Aluminum Hydroxide | Al(OH)₃ | 78.00 | Insoluble | Yes | Antacids, water purification |
Among these, zinc hydroxide is unique because of its amphoteric nature, making it react with both acids and bases.
Safety and Handling of Zinc Hydroxide
Health Hazards
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Inhalation of Zn(OH)₂ dust can cause respiratory irritation.
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Direct skin contact may lead to mild irritation.
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Ingesting large amounts may result in stomach discomfort.
Storage and Disposal Guidelines
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Store in a cool, dry place away from acids and bases.
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Dispose of according to environmental safety regulations.
Zinc hydroxide (Zn(OH)₂) is a versatile chemical compound with a molar mass of 99.39 g/mol. Its unique amphoteric nature allows it to react with both acids and bases, making it useful in medicine, coatings, water treatment, and industrial applications.
With its important chemical and physical properties, Zn(OH)₂ plays a significant role in scientific and industrial fields.
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