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 is the importance of metal oxides?
With the advancement of nanochemistry, the uses and application of metal oxides are also progressing. Metal oxides are basically ionic crystals and found many uses in chemistry, agriculture, medicine, etc. Titanium dioxide is the widely used metal oxide in paint. Also, metal oxides are used as sensors and biosensors nowadays. The integration of the target molecule is easy when we use metal surfaces. The sensitive properties of metal oxide can be improved by tailoring the surface of metal oxide.
2. Can metal oxides react with bases?
Some metal oxides, like aluminum oxide and zinc oxide, show both acidic and basic behaviour. Such metal oxides which react with both acids and bases to produce salts and water are known as amphoteric oxides.
Al2O3 + 2NaOH → 2NaAlO2 + H2O
3. Why does a blue color appear when copper(II) oxide reacts with sulphuric acid?
Copper(II) oxide is a metal oxide which is seen as a black-colored solid. Since it has a basic property it does react with sulfuric acid and can produce copper sulphate and water. In copper, sulfate copper is in +2 oxidation state. Also, copper sulphate is a salt that can produce copper ions in the solution. During the formation of copper sulpate, the splitting of t2g and eg levels of copper changes, and it absorbs a reddish-orange light. Due to this absorption, the solution is seen as blue-colored.
