What is Zinc Oxide? Formula, Structure, and Key Applications
Zinc oxide is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. It appears in medicines, sunscreen, paints, rubber, and electronics, making it a vital concept for students.
What is Zinc Oxide in Chemistry?
A zinc oxide is a white, inorganic compound with the chemical formula ZnO. It consists of zinc and oxygen ions. This concept appears in chapters related to oxides, metal compounds, and chemical reactions, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula of zinc oxide is ZnO. It consists of one zinc atom (Zn, atomic number 30) and one oxygen atom (O, atomic number 8) bonded together. It is categorized under inorganic, amphoteric metal oxides.
Preparation and Synthesis Methods
Zinc oxide can be prepared both in the laboratory and on an industrial scale. In labs, ZnO is commonly formed by heating zinc carbonate (ZnCO₃) or zinc hydroxide (Zn(OH)₂), which decomposes to ZnO and releases CO₂ or H₂O. In industry, zinc metal is heated in air:
2Zn(s) + O₂(g) → 2ZnO(s)
Alternatively, roasting zinc sulfide ores also gives ZnO after intermediate steps. The product appears as a white powder.
Physical Properties of Zinc Oxide
Zinc oxide is a white powder with no odor. It is insoluble in water but dissolves in acids and alkalis, showing amphoteric behavior. Its melting point is very high (about 1975°C), and it has hexagonal (wurtzite) and cubic (zinc blende) crystal forms. It is used as a pigment because of its brightness and opacity.
Chemical Properties and Reactions
Zinc oxide is amphoteric. It reacts with acids to form zinc salts and with strong bases to form zincates. For example:
ZnO + 2HCl → ZnCl₂ + H₂O
ZnO + 2NaOH + H₂O → Na₂[Zn(OH)₄]
It is also stable at high temperatures and can act as a mild oxidizing or reducing agent in some specialized conditions.
Frequent Related Errors
- Confusing ZnO with other metal oxides that are basic or entirely acidic.
- Thinking ZnO dissolves in water—it does not, but it reacts with acids/bases.
- Believing all white pigments are harmful—ZnO is non-toxic, unlike lead white.
- Mixing up “calamine” with natural minerals (calamine lotion contains ZnO, not the old mineral called calamine).
Uses of Zinc Oxide in Real Life
Zinc oxide is widely used in industries like cosmetics, medicine, paints, ceramics, glass, adhesives, and rubber. It appears in everyday life as a sunscreen ingredient (reflecting UV rays), in diaper rash creams, calamine lotion, anti-dandruff shampoos, first-aid ointments, and even in certain food fortification processes. It is also a pigment (zinc white) in paints.
Relation with Other Chemistry Concepts
Zinc oxide is closely related to topics such as amphoteric oxides and transition elements, helping students build a conceptual bridge between various chapters. Its chemical reactivity also links to acid-base reactions and the general study of chemical equations.
Step-by-Step Reaction Example
1. Start with the reaction setup.2. Write the balanced equation.
3. Explain each intermediate.
4. Final answer: Zinc oxide acts as a base here and dissolves in acid to give a salt and water.
Lab or Experimental Tips
Remember zinc oxide by its white, powdery appearance and its use as a sunscreen or ointment ingredient. Vedantu educators often remind students that ZnO’s amphoteric nature means “amphi = both”—it reacts with both acids and bases.
Try This Yourself
- Write the IUPAC name of ZnO.
- Decide if zinc oxide dissolves in water, acid, or base.
- Give two real-life examples of zinc oxide use.
Final Wrap-Up
We explored zinc oxide—its structure, properties, reactions, and real-life importance. For more in-depth explanations and exam-prep tips, explore live classes and notes on Vedantu. Zinc oxide is more than just a chemical formula; it is a bridge between theory and practical life in chemistry education.
| Zinc Oxide Quick Facts | Details |
|---|---|
| Molecular Formula | ZnO |
| Appearance | White powder |
| Solubility | Insoluble in water, soluble in acids & strong bases |
| Melting Point | ~1975°C |
| Amphoteric? | Yes |
| Main Uses | Medicines, sunscreen, ointments, rubber, paint pigment |
Want to explore more about related topics? Learn more on Amphoteric Oxides, and Chemical Reactions and Equations with Vedantu.
FAQs on Zinc Oxide: Properties, Structure, and Everyday Uses
1. What is the chemical formula and basic identity of zinc oxide?
The chemical formula for zinc oxide is ZnO. It is an inorganic compound composed of one zinc ion (Zn²⁺) and one oxide ion (O²⁻). In its pure form, it appears as a white, odourless, crystalline solid or powder that is nearly insoluble in water.
2. What are the key physical and chemical properties of zinc oxide?
Zinc oxide possesses several distinct properties that make it useful in various applications:
- Appearance: It is a white, odourless powder.
- Solubility: It is insoluble in water but dissolves in both acids and strong alkalis.
- Melting Point: It has a very high melting point of approximately 1975°C.
- Amphoteric Nature: It reacts with both acids and bases, a key chemical characteristic.
- Semiconductor Property: It has a wide band gap, making it an important n-type semiconductor.
- Thermochromism: It reversibly changes colour from white to yellow upon heating.
3. What is the significance of the wurtzite crystal structure for zinc oxide?
The most common crystal structure of zinc oxide is the hexagonal wurtzite structure. The significance of this specific arrangement of Zn²⁺ and O²⁻ ions is that it results in properties like piezoelectricity (the ability to generate an electric charge in response to applied mechanical stress) and makes it a direct bandgap semiconductor. These structural properties are fundamental to its use in sensors, transducers, and electronic devices.
4. Why is zinc oxide classified as an amphoteric oxide? Explain with chemical reactions.
Zinc oxide is classified as an amphoteric oxide because it exhibits dual behaviour, reacting with both acids and strong bases to form salt and water. This is a characteristic property of some metal oxides.
- Reaction with Acid (e.g., HCl): ZnO + 2HCl → ZnCl₂ + H₂O
- Reaction with Base (e.g., NaOH): ZnO + 2NaOH → Na₂ZnO₂ + H₂O (Sodium Zincate)
5. How does zinc oxide provide protection in sunscreens?
In sunscreens, zinc oxide functions as a physical blocker or mineral filter. Instead of being absorbed into the skin, it forms a protective barrier on the surface. This barrier works by reflecting and scattering harmful ultraviolet (UV) radiation, including both UVA and UVB rays, preventing them from penetrating the skin and causing damage.
6. What are some important everyday uses of zinc oxide?
Zinc oxide is a versatile compound found in many everyday products due to its unique properties. Key examples include:
- Skincare and Cosmetics: Used in sunscreens, calamine lotions, diaper rash creams, and anti-dandruff shampoos for its protective and soothing properties.
- Industrial Manufacturing: It is a crucial additive in rubber manufacturing (vulcanization activator), which improves heat resistance and durability.
- Paints and Pigments: Used as a white pigment called 'zinc white' in paints, valued for its brightness and opacity.
- Ceramics and Glass: Added to ceramic glazes and glass formulations to improve their thermal and optical properties.
7. Why does pure zinc oxide appear yellow when hot but white when cold?
This colour change is a classic example of thermochromism and is due to the formation of metal excess defects. When heated, zinc oxide loses a small amount of oxygen, creating anion vacancies and releasing free electrons (ZnO → Zn²⁺ + ½O₂ + 2e⁻). These free electrons get trapped in the crystal lattice, forming F-centres that absorb light in the violet-blue region of the spectrum, causing the compound to appear yellow. Upon cooling, the compound reabsorbs oxygen from the air, the defects are healed, and it reverts to its original white colour.
8. What are the main industrial methods for preparing zinc oxide?
The two primary industrial methods for preparing zinc oxide are:
- Indirect Process (French Process): High-purity zinc metal is vaporised at high temperatures and then reacted with oxygen in the air. The resulting zinc oxide is cooled and collected. This method produces high-purity ZnO.
- Direct Process (American Process): Zinc-containing ores or smelter by-products are heated with a carbon source like coal to produce zinc vapour, which is then oxidised to form zinc oxide. This process yields a lower purity product suitable for applications like rubber manufacturing.
9. Why is 'zinc white' (ZnO) a superior pigment compared to 'white lead'?
'Zinc white' is considered superior to the traditional 'white lead' (basic lead carbonate) pigment for two main reasons. Firstly, zinc oxide is non-toxic, whereas lead compounds are highly poisonous, making ZnO much safer for use. Secondly, zinc white does not tarnish or darken when exposed to sulphur compounds (like H₂S) present in polluted air, as it does not form a coloured sulphide. In contrast, white lead reacts with H₂S to form black lead sulphide (PbS), causing the paint to discolour over time.
10. What is the importance of zinc oxide's wide band gap in modern electronics?
Zinc oxide has a wide direct band gap of approximately 3.3 eV (electronvolts). This is highly significant because it makes ZnO an excellent n-type semiconductor. Its ability to be transparent to visible light while strongly absorbing UV radiation makes it ideal for creating transparent conducting films used in LCDs and solar cells. This property also enables its use in UV-light-emitting diodes (LEDs), photodetectors, and various types of chemical sensors.
