Question

Select the correct order of acidic nature of metal oxide:
(This question has multiple correct options.)
(A) $MnO(B) $CrO(C) $MnO(D) $CrO

Answer 1

Hint: If we are comparing the strength of acidity of metal oxides of the same metal, then we can say that higher the oxidation state of the metal in oxides, higher will be the acidity of the corresponding oxides.


Complete step by step solution:
Actually all metal oxides show basic nature. Here, we are being asked to compare the acidity of various oxides of the same metal. Let’s see how to compare its acidity.
- According to the definition of acids of Lewis, the acid is a compound which can accept an electron. Now, we are given various oxides of metals in which the oxidation state of metal is not the same. So, we can say that higher the oxidation state of the metal, higher will be its tendency to accept electrons and as a result it will be a more acidic compound.
- So, we will find the oxidation states of the metals in oxides and can say that oxides with metal having high oxidation state will be more acidic in nature.
- Oxidation state of Mn in MnO:
We can write that Overall charge on MnO= Oxidation state of Mn + Oxidation state of O
Therefore 0 = Oxidation state of Mn + (-2)
Oxidation state of Mn in MnO = 0+2 = +2
Oxidation state of Mn in $M{{n}_{2}}{{O}_{3}}$ :
Overall charge on $M{{n}_{2}}{{O}_{3}}$ = 2(Oxidation state of Mn) + 3(Oxidation state of O)
0 = 2(Oxidation state of Mn) + 3(-2)
Oxidation state of Mn in $M{{n}_{2}}{{O}_{3}}$ = $\dfrac{+6}{2}=+3$
Oxidation state of Mn in $M{{n}_{3}}{{O}_{4}}$ :
Overall charge on $M{{n}_{3}}{{O}_{4}}$ = 3(Oxidation state of Mn) + 4(Oxidation state of O)
Therefore 0 = 3(Oxidation state of Mn) + 4(-2)
Oxidation state of Mn in $M{{n}_{3}}{{O}_{4}}$ = $\dfrac{8}{3}=+2.66$
Oxidation state of Mn in $M{{n}_{2}}{{O}_{7}}$:
Overall charge on $M{{n}_{2}}{{O}_{7}}$ = 2(Oxidation state of Mn) + 7(Oxidation state of O)
Therefore 0 = 2(Oxidation state of Mn) + 7(-2)
Oxidation state of Mn in $M{{n}_{2}}{{O}_{7}}$ = $\dfrac{14}{2}=+7$
Thus, we can arrange the oxides of manganese in the increasing order of oxidation states of Mn in them and that will also be the order of acidity.
So, the order of acidity in Manganese oxides is $MnONow, we will do the same for Chromium oxides.
- Oxidation state of Cr in CrO:
We can write that Overall charge on CrO= Oxidation state of Cr + Oxidation state of O
Therefore 0 = Oxidation state of Cr + (-2)
Oxidation state of Cr in CrO = 0+2 = +2
Oxidation state of Cr in $C{{r}_{2}}{{O}_{3}}$ :
Overall charge on $C{{r}_{2}}{{O}_{3}}$ = 2(Oxidation state of Cr) + 3(Oxidation state of O)
0 = 2(Oxidation state of Cr) + 3(-2)
Oxidation state of Cr in $C{{r}_{2}}{{O}_{3}}$ = $\dfrac{+6}{2}=+3$
Oxidation state of Cr in $Cr{{O}_{2}}$ :
Overall charge on $Cr{{O}_{2}}$ = Oxidation state of Cr + 2(Oxidation state of O)
Therefore 0 = Oxidation state of Cr + 2(-2)
Oxidation state of Cr in $Cr{{O}_{2}}$ = $+4+0=+4$
Oxidation state of Cr in $Cr{{O}_{3}}$:
Overall charge on $Cr{{O}_{3}}$ = Oxidation state of Cr + 3(Oxidation state of O)
Therefore 0 = Oxidation state of Cr + 3(-2)
Oxidation state of Cr in $Cr{{O}_{3}}$ = $+6$
Thus, the correct order of acidity of chromium oxides is $CrO

So, we can say that both options (A) and (D) are correct.


Note: We can also say that in comparison of acidity of oxides of the same metal, the oxide which has a high number of oxygen per an atom of metal will have higher acidity. Do not forget that oxides of metal are basic in nature.