CrO3 and Mn2O7 are considered as acidic oxides although they are metallic oxides.Why?
Answers
Metallic oxides are basic in nature because they react with dilute acids to form salt and water. They also react with water to form metal hydroxides which are alkaline in nature, as these metal hydroxides release OH- ions in solution.
Therefore non metallic oxides are acidic in nature.
Answer:
Generally Group 1 and Group 2 elements form bases called base anhydrides or basic oxides.
Basic oxides are the oxides of metals. If soluble in water, they react with water to produce hydroxides (alkalies).
Amphoteric oxides are metallic oxides, which show both basic as well as acidic properties. When they react with an acid, they produce salt and water, showing basic properties. While reacting with alkalies they form salt and water showing acidic properties
The oxides of elements in a period become progressively more acidic as one goes from left to right in a period of the periodic table. For example, in third period, the behavior of oxides changes as follows:
Basic
Na
2
O,MgO
Amphoteric
Al
2
O
3
,SiO
2
Acidic
P
4
O
10
,SO
3
,Cl
2
O
7
Generally, for transition metal oxides, the lowest oxidation state is the most basic, since it can donate lone pairs of electrons and function as a Lewis base. Higher oxidation states are short of electrons, meaning they can accept lone pairs and function as Lewis acids.
MnO has the lowest oxidation state, so it is the most basic while Mn
2
O
7
is actually acidic.
Mn
2
O
7
+H
2
O→2HMnO
4