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Class 11th

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5 months ago

Class 11th The S-block Elements

Lithium hydride can be used to prepare other useful hydrides. Beryllium hydride is one of them. Suggest a route for the preparation of beryllium hydride starting from lithium hydride. Write chemical equations involved in the process.
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Payal Gupta

Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

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

New answer posted

5 months ago

Class 11th The S-block Elements

When water is added to compound (A) of calcium, solution of compound (B) is formed. When carbon dioxide is passed into the solution, it turns milky due to the formation of compound (C). If excess of carbon dioxide is passed into the solution milkiness disappears due to the formation of compound (D). Identify the compounds A, B, C and D. Explain why the milkiness disappears in the last step .?
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Payal Gupta

Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

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

New answer posted

5 months ago

Class 11th The S-block Elements

The stability of peroxide and superoxide of alkali metals increase as we go down the group. Explain giving reason.?
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Payal Gupta

Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

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

New answer posted

5 months ago

Class 11th The S-block Elements

When a metal of group 1 was dissolved in liquid ammonia, the following observations were obtained:

(i) Blue solution was obtained initially.

(ii) On concentrating the solution, blue colour changed to bronze colour. How do you account for the blue colour of the solution?.

Give the name of the product formed on keeping the solution for some time.
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Payal Gupta

Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

(i) The alkali metals dissolve in liquid ammonia and give a blue solution, which is conductive in nature. A solution of sodium in liquid ammonia at -30C conducts electricity. The ammoniated electrons are responsible for the blue color of the solution as they absorb energy in the visible region of light and impart blue color to the solution. Both the ammoniated cations and ammoniated electrons are responsible for the electrical conductivity of the solution.

Na + (x+y)NH3→ [Na (NH3)x]+ + [e (NH3)y]−

(ii) The blue color changes to bronze color in concentrated solution

...more

New question posted

5 months ago

Class 11th The S-block Elements

3. When a metal of group 1 was dissolved in liquid ammonia, the following observations were obtained:

(i) Blue solution was obtained initially.

(ii) On concentrating the solution, blue colour changed to bronze colour. How do you account for the blue colour of the solution?

Give the name of the product formed on keeping the solution for some time.
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New answer posted

5 months ago

Class 11th The S-block Elements

Present a comparative account of the alkali and alkaline earth metals with respect to the following characteristics:::

(i) Tendency to form ionic / covalent compounds

(ii) Nature of oxides and their solubility in water

(iii) Formation of oxosalts

(iv) Solubility of oxosalts

(v) Thermal stability of oxosalts
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Payal Gupta

Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

(i) Alkaline earth metal compounds are less ionic than alkali metals because of small size and more effective nuclear charge.

(ii) Oxides of alkali metals are more basic than alkaline earth metals. This are water soluble and highly exothermic. The hydroxides of alkaline earth metals are less basic than alkali metals.

(iii) Alkaline earth metals give oxosalts. The reactivity of alkali metals is faster than the reactivity of alkaline earth metal. The reactivity of alkaline earth metal is less due to small size and more effective nuclear charge.

(iv) The oxo salts of alka

...more

New answer posted

5 months ago

Class 11th Some Basic Principles and Techniques

54. Nucleophile is a species that should have 

(i)  A pair of electrons to donate 

(ii) Positive charge 

(iii) Negative charge 

(iv) Electron deficient species
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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

54. Options (i) and (iii) are correct since nucleophiles are negatively charged or electron rich (as contains lone pair of electrons) species. 

New answer posted

5 months ago

Class 11th The S-block Elements

The s-block elements are characterised by their larger atomic sizes, lower ionisation enthalpies, invariable +1 oxidation state and solubilities of their oxosalts.In the light of these features describe the nature of their oxides, halides and oxosalts.
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Payal Gupta

Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

Alkali metals are ionic in nature due to their larger size. They have +1 oxidation states. Alkali metals forms three types of oxides such as peroxides, superoxides and normal oxides. The basic character of normal oxides increases from lithium oxide to caesium oxide.

The halides of alkali metals are also ionic except lithium halide. Lithium halide is covalent in nature because of small size and high polarizing power.

Oxosalts of alkali metal are solid water-soluble ionic compounds. Oxosalts of lithium show different properties due to small size of lithium.

New answer posted

5 months ago

Class 11th Some Basic Principles and Techniques

55. Nucleophile is a species that should have 

(i) A pair of electrons to donate 

(ii) Positive charge 

(iii) Negative charge 

(iv) Electron deficient species
0 Follower 6 Views

A
alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

55. Options (i) and (iii) are correct since nucleophiles are negatively charged or electron rich (as contains lone pair of electrons) species. 

New answer posted

5 months ago

Class 11th Some Basic Principles and Techniques

53. Which of the following pairs are not functional group isomers?

(i) II and III 

(ii) II and IV 

(iii) I and IV 

(iv) I and II 
0 Follower 1 View

A
alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

53. Options (i) and (ii) are correct since two or more compounds with same molecular formula but different functional groups are known as functional isomers. In the given compounds- 

I. Aldehydic group. II. Ketonic group. III. Ketonic group. IV. Aldehydic group. So, II and III, I and IV are not functional isomers.

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