1

### AIPMT 2011 Mains

Match List-I with List-II for the compositions of substances and select the correct answer using the code given above.

List-I
(Substances)
List-II
(Composition)
(A) Plaster of Pairs (i) CaSO4$\cdot$2H2O
(B) Epsomite (ii) CaSO4$\cdot$1/2 H2O
(C) Kieserite (iii) MgSO4$\cdot$7H2O
(D) Gypsum (iv) MgSO4$\cdot$H2O
(v) CaSO4
A
(A)-(iii),  (B)-(iv),  (C)-(i),  (D)-(ii)
B
(A)-(ii),  (B)-(iii),  (C)-(iv),  (D)-(i)
C
(A)-(i),  (B)-(ii),  (C)-(iii),  (D)-(iv)
D
(A)-(iv),  (B)-(iii),  (C)-(ii),  (D)-(i)

## Explanation

(A) Plaster of paris = CaSO4.${1 \over 2}$H2O

(B) Epsomite = MgSO4.7H2O

(C) Kieserite = MgSO4.H2O

(D) Gypsum = CaSO4.2H2O
2

### AIPMT 2010 Prelims

Which one of the following compounds is a peroxide?
A
KO2
B
BaO2
C
MnO2
D
NO2

## Explanation

3

### 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 :

4

### 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.

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