1
MCQ (Single Correct Answer)

AIPMT 2008

Equimolar solutions of the following were prepared in water separately. Which one of the solutions will record the highest pH?
A
MgCl2
B
CaCl2
C
SrCl2
D
BaCl2

Explanation

Equimolar solutions of the given chlorides when prepared in water forms their respective hydroxides.

SrCl2 + 2H2O $$ \to $$ Sr(OH)2 + 2HCl

BaCl2 + 2H2O $$ \to $$ Ba(OH)2 + 2HCl

MgCl2 + 2H2O $$ \to $$ Mg(OH)2 + 2HCl

CaCl2 + 2H2O $$ \to $$ Ca(OH)2 + 2HCl

Be(OH)2 is amphoteric, but the hydroxides of other alkaline earth metals are basic. The basic strength increases down the group. Hence higher the basic character higher will be the pH.
2
MCQ (Single Correct Answer)

AIPMT 2007

In which of the following the hydration energy is higher than the lattice energy?
A
MgSO4
B
RaSO4
C
SrSO4
D
BaSO4

Explanation

Hydration energy of sulphate decreases on moving down the group-II. Mg2+ is smaller than other ions of group II, so Mg2+ is readily hydrated and hence MgSO4 has higher hydration energy than the lattice energy.
3
MCQ (Single Correct Answer)

AIPMT 2007

The correct order of increasing thermal stability of K2CO3, MgCO3, CaCO3 and BeCO3 is
A
BeCO3 < MgCO3 < CaCO3 < K2CO3
B
MgCO3 < BeCO3 < CaCO3 < K2CO3
C
K2CO3 < MgCO3 < CaCO3 < BeCO3
D
BeCO3 < MgCO3 < K2CO3 < CaCO3

Explanation

As the basicity of metal hydroxides increases down the group from Be to Ba, the thermal stability of their carbonates also increases in the same order. Further group 1 compounds are more thermally stable than group 2 because their hydroxide are much basic than group 2 hydroxides therefore, the order of thermal stability is

BeCO3 < MgCO3 < CaCO3 < K2CO3
4
MCQ (Single Correct Answer)

AIPMT 2006

The correct order of the mobility of the alkali metal ions in aqueous solution is
A
Rb+ > K+ > Na+ > Li+
B
Li+ > Na+ > K+ > Rb+
C
Na+ > K+ > Rb+ > Li+
D
K+ > Rb+ > Na+ > Li+

Explanation

Ionic radii of alkali metals in water follows the order
Li+ > Na+ > K+ > Rb+ > Cs+

Thus in aqueous solution due to larger ionic radius Li+ has lowest mobility and hence the correct order of ionic mobility is

Rb+ > K+ > Na+ > Li+

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