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1

AIPMT 2010 Mains

The compound A on heating gives a colourless gas and a residue that is dissolved in water to obtain B. Excess of CO2 is bubbled through aqueous solution of B, C is formed which is recovered in the solid form. Solid C on gentle heating gives back A. The compound is
A
CaCO3
B
Na2CO3
C
K2CO3
D
CaSO4$$\cdot$$2H2O

Explanation

A $$\buildrel \Delta \over \longrightarrow$$ colourless gas + residue

Residue + H2O $$\to$$ B $$\buildrel {excess\,\,C{O_2}} \over \longrightarrow$$ C $$\buildrel \Delta \over \longrightarrow$$ A

This is possible only when ‘A’ is CaCO3. The reactions are as follow :

2

AIPMT 2010 Prelims

Which of the following alkaline earth metal sulphates has hydration enthalpy higher than the lattice enthalpy?
A
CaSO4
B
BeSO4
C
BaSO4
D
SrSO4

Explanation

The hydration enthalpy of BeSO4 is higher than its lattice energy. Within group 2, the hydration energy decreases down the group while lattice energy is almost the same.
3

AIPMT 2010 Prelims

Property of the alkaline earth metals that increases with their atomic number
A
solubility of their hydroxides in water
B
solubility of their sulphates in water
C
ionization energy
D
electronegativity

Explanation

On moving down the group, basic nature of these hydroxides increases due to low ionization enthalpies because M-O bond in MOH is weak and thus break to give OH ions in the solution.
4

AIPMT 2009

Which of the following oxides is not expected to react with sodium hydroxide?
A
CaO
B
SiO2
C
BeO
D
B2O3

Explanation

NaOH is a strong alkali. It combines with acidic and amphoteric oxides to form salts. Since CaO is a basic oxide hence does not reacts with NaOH.

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