Reaction between Metallic Oxide and Acid: An Introduction
The uses and applications of Metal oxide nanoparticles are increasing day by day. They found applications in various fields like chemistry, medicine, agriculture, etc. Titanium dioxide is the widely used metal oxide in paints. What are these metal oxides? Metal oxides are ionic crystals having metal cations and oxygen anions. They can react with acids just like the. bases do. In this article, we will discuss metallic oxide reactions with acids in detail.
Metal Oxides
Metal oxides contain a metal cation and an oxygen anion. They are crystalline solids that react with water to give a basic solution of metal hydroxide, and their reaction with acids produces salts. Metal oxides are ionic crystals.
In the periodic table, group 1 and group 2 elements are metals, namely alkaline and earth metals, respectively. Alkali metals form metal oxides M2O, peroxide M2O2 and superoxide MO2.
In general, metal oxides can react with water and form metal hydroxide solutions. The reaction of metal oxide with water can generally be represented as:
M2O + H2O → 2MOH
MO + H2O → M(OH)2
Since the product of reactions of metal oxide with water is basic hydroxide, the metal oxide is also known as basic oxide. Hence their reaction with acid is like a typical acid-base reaction and forms salt and water. Hence the reaction between an acid and metal oxide is a neutralisation reaction.
Reaction of Metal Oxide With Acids
Metal oxide can react with acid and produce salt and water. The reaction is a neutralisation reaction. Generally, the reaction of metal oxide with acid can be represented as
M2O + 2HCl → 2MCl + H2O
One of the important metal oxides is calcium oxide. It is also known as quick lime. It found applications in the steel industry and water purification. CaO can react with HCl and form CaCl2 and water.
CaO + 2HCl → CaCl2 + H2O
Magnesium oxide MgO can be used as a thermal conductor, and its reaction with the acid HCl produces Magnesium chloride and water.
MgO + 2 HCl → MgCl2 + H2O
Periodic Trends in the Reaction of Metal Oxides with Acids
Periodic trends in the acidity or basicity of metal oxides are thoroughly studied, thereby we can predict their reactivity with acids
The basicity of metal oxide increases down the group.
Hence in alkaline earth metals, the order of basicity is BeO<MgO<CaO<SrO. So SrO will react faster with HCl than BeO because BeO is more basic.
SrO + 2HCl → SrCl2 + H2O
During the period of moving from left to right acidity increases or basicity decreases. Hence CaO is more acidic or less basic than Na2O. So Na2O will react faster than MgO in an acidic medium because Na2O is more basic than MgO.
Na2O + 2HCl → 2NaCl + H2O
In transition metals, since they can show a variable oxidation state, the order of acidity will depend on the oxidation state of the metal. As the oxidation state increases acidity increases or basicity decreases. Hence the oxide of manganese MnO (in which the oxidation state of Mn is +2) is basic and will react faster in an acidic medium compared to the oxide Mn2O7 (in which the oxidation state of Mn is,+7 hence more acidic than MnO).
As a general rule transition metals having oxidation states +1, +2, +3 are ionic oxides and are more basic than metals having an oxidation state of +4, +5, +6, and +7. Hence transition metals having oxidation state below +4 will react faster in aqueous acidic medium than the metals having oxidation state greater than four.
CoO + 2HCl → CoCl2 + 2H2O
Transition metal oxides with oxidation state of metal is +4 is amphoteric. Which means that they can react with both acid and water. For example vanadium oxide VO2, is amphoteric and can react with both acid and base.
VO2 + 2HCl → VOCl2 +H2O
VO2 + 2NaOH → Na2VO3 + H2O
Key Features
Metal oxides are ionic crystals with metal cations and oxygen anions.
Metal oxides have properties of bases.
Metal oxides can react with acids.
The reaction of metal oxide with acid is a neutralization reaction.
FAQs on Reaction of Metallic Oxide with Acid
1. What happens when a metallic oxide reacts with an acid?
When a metallic oxide reacts with an acid, it produces a salt and water. This reaction demonstrates the characteristic basic nature of metallic oxides. The general chemical equation for this process is: Metallic Oxide + Acid → Salt + Water. For instance, when magnesium oxide reacts with hydrochloric acid, it forms magnesium chloride (a salt) and water.
2. What is the nature of most metallic oxides, and how can it be demonstrated?
Most metallic oxides are basic in nature. This can be demonstrated through their reaction with acids to form salt and water, which is a classic neutralization reaction. Additionally, when soluble metallic oxides like sodium oxide or calcium oxide dissolve in water, they form metal hydroxides (bases), which turn red litmus paper blue, confirming their basicity.
3. Can you provide some examples of reactions between metallic oxides and acids?
Certainly. Here are a few common examples of reactions between metallic oxides and acids, relevant for the 2025-26 syllabus:
- Copper(II) Oxide with Hydrochloric Acid: CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l)
- Calcium Oxide with Sulphuric Acid: CaO(s) + H₂SO₄(aq) → CaSO₄(aq) + H₂O(l)
- Zinc Oxide with Hydrochloric Acid: ZnO(s) + 2HCl(aq) → ZnCl₂(aq) + H₂O(l)
4. Why does the solution turn blue-green when black Copper(II) Oxide reacts with Hydrochloric Acid?
Copper(II) Oxide (CuO) is a black solid. During the reaction with Hydrochloric Acid (HCl), a new substance, Copper(II) Chloride (CuCl₂), is formed. Copper(II) Chloride is soluble in water and imparts a distinct blue-green colour to the resulting solution. The original black solid is consumed in the reaction, causing it to disappear and be replaced by the coloured aqueous solution.
5. Are all metallic oxides basic? Explain the concept of amphoteric oxides.
No, not all metallic oxides are exclusively basic. Certain metallic oxides are known as amphoteric oxides, which means they can exhibit both acidic and basic properties. They react with both acids and strong bases to produce salt and water. Two primary examples are:
- Zinc Oxide (ZnO): It reacts with an acid like HCl and also with a base like NaOH.
- Aluminium Oxide (Al₂O₃): It reacts with acids like H₂SO₄ and also with strong bases like NaOH.
6. What type of reaction is the reaction between a metallic oxide and an acid?
The reaction between a metallic oxide and an acid is primarily classified as a neutralization reaction. This is because it involves a basic substance (the metallic oxide) reacting with an acidic substance (the acid) to form neutral products, salt and water. It can also be viewed as a double displacement reaction, where the metal cation and hydrogen ion exchange places.
7. How does the reaction of a metallic oxide with an acid differ from the reaction of a non-metallic oxide with a base?
These two reactions are chemical opposites that illustrate a fundamental principle in chemistry:
- Metallic Oxide + Acid: Metallic oxides are typically basic. They neutralize acids. Example: MgO (basic) + 2HCl (acid) → MgCl₂ + H₂O.
- Non-metallic Oxide + Base: Non-metallic oxides (like CO₂, SO₃) are typically acidic. They neutralize bases. Example: CO₂ (acidic) + 2NaOH (base) → Na₂CO₃ + H₂O.
In essence, both are neutralization reactions, but one confirms the basic nature of metallic oxides, while the other confirms the acidic nature of non-metallic oxides.
8. What is some practical importance of metallic oxides in daily life?
Metallic oxides are crucial in many applications. For example, Iron(III) oxide is used as a red pigment and in producing magnetic tapes. Titanium dioxide is a key ingredient in sunscreen and white paint because it is highly opaque and non-toxic. Zinc oxide has mild antiseptic properties and is used in skin ointments and creams.
