The S-block Elements

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The element from group 2 is beryllium. Be (OH)₂ is amphoteric. It reacts with both acids and bases. It reacts with acid to form beryllium chloride and it reacts with base to form beryllate ion which is soluble in sodium hydroxide. The reaction is shown below.

Be (OH)₂+2OH−→ [Be (OH)₄]²⁻

Be (OH)₂+2HCl→BeCl₂+2H₂O

Beryllium sulfate are readily soluble in water.

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These two elements have similar properties because of their similar atomic and ionic radii.

(i) Both are lighter element and harder than the other metals in their respective groups.

(ii) The halides of both elements, LiCl and MgCl₂ are soluble in ethanol.

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(i) O₂²⁻+ 2H₂O → H₂O₂+2OH⁻

(ii) 2O₂⁻+2H₂O→2OH⁻+H₂O₂+O₂

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Alkali metals forms oxide when reacted with air. Lithium forms monoxide, sodium forms peroxide and potassium forms superoxide.

4Li+O₂→2Li₂O

Na+O₂→Na₂O₂

 K+O₂→KO₂

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Lithium has the highest negative reduction potential value. Due to the small size of lithium it has the highest ionization enthalpy. Due to this, the reducing power of lithium is the highest in an aqueous solution.

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The element imparts yellow colour to the flame in flame test which means the element of group 1 is sodium. Sodium is used in the transmission of nerve signals and transport of sugars and amino acids into cells. Reactions are shown below.

2Na+O₂→Na₂O₂

4Na+O₂→2Na₂O

2Na₂O+O₂→2Na₂O₂

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In group 2, only beryllium is amphoteric in nature which means it reacts with both acids and bases. Also, beryllium only forms covalent oxide due to the covalent nature. So, the element is beryllium.

It reacts with acid to form beryllium chloride and it reacts with base to form beryllate ion which is soluble in sodium hydroxide. The reaction is shown below.

Be (OH)₂+2OH⁻ → [Be (OH)₄]²⁻

Be (OH)₂+2HCl →BeCl₂+2H₂O

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Beryllium being least reactive does not form hydride by direct heating with dihydrogen. It is prepared by reacting it with lithium aluminum hydride. The reactions are shown below.

8LiH + Al₂Cl₆→2LiAlH₄+6LiCl

2BeCl₂+LiAlH₄→2BeH₂+LiCl+AlCl₃

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Compound A reacts with water to form compound B. So, the compound A is calcium oxide. When water is added to calcium oxide, calcium hydroxide is formed. It is lime water. The compound gives a milky appearance which is compound C. The compound C is calcium carbonate. On passing, excess carbon dioxide milkiness disappears due to the formation of compound D. The compound is calcium hydrogen carbonate. The reactions are as follows:

CaO+H₂O→Ca (OH)₂

Ca (OH)₂+CO2→CaCO₃

Ca (OH)₂+CO₂+H2O→Ca (HCO₃)₂

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As the size of metal ions increases, the stability of peroxides and superoxides increases. Peroxide and superoxide ions combine with a large size of alkali metals. Lithium forms monoxide, sodium forms peroxide and potassium, rubidium and caesium forms superoxide.

Li+O₂→Li₂O

Na+O₂→Na₂O₂

 K+O₂→KO₂