ALKALINE EARTH METALS MCQ
IIT JEE

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1) The solubilities of carbonates decrease down the magnesium group (alkaline earth metals) due to a decrease in:

(AIEEE 2003 - EQUIVALENT TO IIT JEE MAIN)

1) lattice energies of solids 

2) hydration energies of cations 

3) inter-ionic attraction 

4) entropy of solution formation 

Logic:

Solubility of an ionic compound in water decreases with increase in lattice energy but increase with hydration energies. 

In alkaline earth metal group, the hydration energy of cation decreases from top to bottom with increase in the size of cation. However, the lattice energy remains almost unchanged.

Conclusion:

Option 2 is correct.

Related questions

2) The charge/size ratio of a cation determines its polarizing power. Which one of the following sequences represents the increasing order of the polarizing power of the cationic species, K⁺, Ca²⁺, Mg²⁺, Be²⁺? 

(AIEEE 2007) 

1) Ca²⁺ < Mg²⁺ < Be²⁺ < K⁺ 

2) Mg²⁺ < Be²⁺ < K⁺ < Ca²⁺ 

3) Be²⁺ < K⁺ < Ca²⁺ < Mg²⁺ 

4) K⁺ < Ca²⁺ < Mg²⁺ < Be²⁺

Explanation: 

* Polarizing power = charge on the ion / size of the ion

i.e. the polarizing power is directly proportional to charge and inversely related to size of the ion. 

* The decreasing order of size of cations is: K⁺ > Ca²⁺ > Mg²⁺ > Be²⁺ 

* Therefore the increasing correct order of polarizing power is: K⁺ < Ca²⁺ < Mg²⁺ < Be²⁺ 

Conclusion:

Correct option is: '4'.

3) What are the metal ion are present in carnalite?

(EAMCET 2006 ENGINEERING) 

1) Mg²⁺, K⁺ 

2) Al³⁺, Na⁺ 

3) Na⁺, Mg²⁺ 

4) Zn²⁺, Mg²⁺ 

Answer:

Carnallite is KCl.MgCl₂.6H₂O. It shows presence of K⁺ and Mg²⁺ ions in aqueous solutions.

4) Mortar is a mixture of:

(EAMCET 1998 ENGINEERING) 

1) Plaster of Paris + Silica 

2) Slaked lime + Plaster of Paris + H₂O 

3) CaCO₃ + Silica + H₂O 

4) Slaked lime + sand + H₂O

Answer:

Lime mortar is a mixture of one part of Slaked lime (Ca(OH)₂), three parts of Sand (SiO₂) and water. It is converted into calcium silicate with time and becomes hardened. Hence it is used as building material.

Ca(OH)₂ + SiO₂ --------> CaSiO₃ + H₂O

5) The correct order of thermal stability of following carbonates is:

(ADICHEMISTRY) 

1) BaCO₃ > CaCO₃ > SrCO₃ > MgCO₃ 

2) BaCO₃ > SrCO₃ > CaCO₃ > MgCO₃

3) MgCO₃ > CaCO₃ > SrCO₃ > BaCO₃

4) MgCO₃ > CaCO₃ > BaCO₃ > SrCO₃

Logic and Solution:

If the carbonate ion is polarized by the cation, it undergoes decomposition easily upon heating. The polarizing power of alkali metal cations decreases with increase in the size. 

i.e. the order of polarizing power of cations is:

Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺

Hence the correct order of thermal stability of carbonates will be:

BaCO₃ > SrCO₃ > CaCO₃ > MgCO₃

6) The substance not likely to contain CaCO₃ is:

(AIEEE 2003) 

1) a marble statue 

2) calcined gypsum 

3) sea shells 

4) dolomite 

Solution:

* Marble, sea shells and dolomite contain calcium carbonate.

* Dolomite is CaCO₃ + MgCO₃

* Calcined gypsum is dehydrated gypsum otherwise known as plaster of paris. It does not contain any calcium carbonate.

7) ‘Magnalium’ is an alloy of :

(EAMCET 1996 E) 

1) Mg + Zn 

2) Mg + Al 

3) Cu + Zn 

4) Mg + Cu 

Answer:

Magnalium is an alloy of magnesium (1.5 - 2%) and aluminium metals. Due to high strength, low density and ability to resist corrosion; it is used in amking  aircraft and automobile parts.

8) A burning strip of Magnesium in introduced into a jar containing a gas. After sometime the walls of the container are coated with carbon. The gas in the container is:

(EAMCET 1999 E) 

1) O₂ 

2) N₂ 

3) CO₂ 

4) H₂O

Explanation:

The gas in the container is carbon sicne magnesium can reduce carbon dioxide to carbon.

2Mg + CO₂ ---------> 2MgO + C

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