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The s-Block Elements

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Question
CBSEENCH11008383
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In the case of alkali metals, the covalent character decreases in the order

  • MCl> MI>MBr>MF

  • MF> MCl> MBr>MI

  • MF > MCl> MI>MBr

  • MI>MBr>MCl>MF

Solution

D.

MI>MBr>MCl>MF

According to Fajan's rule
Covalent space character space proportional to fraction numerator 1 over denominator Size space of space cation end fraction proportional to space size space of space anion
In the given options, the cation is same but anions are different. Among halogens the order of size is 
F < Cl< Br< I
therefore, Order of covalent character is 
MI> MBr>MCl>MF

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Question
CBSEENCH11008293
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In the replacement reaction



The reaction will be most favourable if M happens to be

  • Na

  • K

  • Rb

  • Li

Solution

C.

Rb

For the reaction,

The reaction will be faster with Rb because lattice energy of RbF is less than LiF, NaF, KF.

Question
CBSEENCH11008429
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In which of the following the hydration energy is higher than the lattice energy? 

  • BaSO4

  • MgSO4

  • RaSO4

  • SrSO4

Solution

B.

MgSO4

Hydration energy of sulphate decreases from top to bottom in an IInd group. Mg2+ is smaller than other ions of that group so Mg2+ is readily hydrated. MgSO4 has higher hydration energy than lattice energy.

Question
CBSEENCH11008343
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Match (I) with list (II) for the  compositions of substances and select the correct answer using the code given below the lists.


 

List I (substance)

 

List II Composition

A.

Plaster of Paris

1.

CaSO4.2H2O

B.

Epsomite

2.

CaSO4. ½ H2O

C.

Kieserite

3.

MgSO4. 7H2O

D.

Gypsum

4.

5.

MgSO4.H2O

CaSO4

  • A

    B

    C

    D

    3

    4

    1

    2

  • A

    B

    C

    D

    2

    3

    4

    1

  • A

    B

    C

    D

    1

    2

    3

    5

  • A

    B

    C

    D

    4

    		 3 2

    1

Solution

B.

A

B

C

D

2

3

4

1

Plaster of paris = CaSO4.1/2 H2O
Epsomite =MgSO4.7H2O
Gypsum = CaSO4.2H2O
Kieserite = MgSO4.H2O

Question
CBSEENCH11008321
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On heating which of the following releases CO2 most easily?

  • K2CO3

  • Na2CO3

  • MgCO3

  • CaCO3

Solution

C.

MgCO3

Order of thermal stability is 
K2CO3 > Na2CO3 > CaCO3 > MgCO3
Thus, MgCO3 releases CO2 most easily
MgCO3 + heat ---> MgO + CO2

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