The s-Block Elements Important Question

Q1. Passing carbon dioxide through slaked lime gives:

  • 1) CaCO3
  • 2) CaO
  • 3) Ca(OH)2
  • 4) CaSO4

Solution

Passing Carbon dioxide through slaked lime gives CaCO3Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '.

Q2. Sodium reacts with water more vigorously than lithium because:

  • 1) It is more electropositive
  • 2) It is a metal
  • 3) It is more electronegative
  • 4) It has a higher atomic weight

Solution

This behaviour of lithium is attributed to its small size and very high hydration energy. Sodium is more electropositive than lithium.

Q3. How will you prepare sodium carbonate by Solvay Process?

Solution

Sodium carbonate is prepared by passing carbon dioxide through ammonia that gives ammonium carbonate. Subsequently ammonium carbonate is converted to ammonium hydrogen carbonate that reacts with sodium chloride to precipitate out sodium hydrogen carbonate.

Sodium hydrogen carbonate later forms sodium carbonate. 2NH3  + H2O + CO2  (NH4)2CO3 (NH4)2CO3  +  H2O + CO2 2NH4HCO3 2NH4HCO3   + NaCl    NH4Cl + NaHCO3  2NaHCO3 Na2CO3 + CO2 + H2O

Q4. We can get beryllium hydride by:

  • 1) Treating BeCl2 with LiAlH4.
  • 2) Treating BeCl2 with H2
  • 3) Treating Be with LiAlH4.
  • 4) Treating Be with H2

Solution

We can get beryllium hydride by treating beryllium chloride with LiAlH4.2BeCl2   +   LiAlH4    2BeH+ LiCl + AlCl3

Q5. Be can show coordination number four while other members show a value of six. This is because of:

  • 1) High ionization enthalpy of Be
  • 2) Non availability of d orbitals in Be
  • 3) Small size of Be
  • 4) Availability of d orbitals in Be

Solution

Due to non availability of d orbitals in Be, it can show coordination number four while other members show a value of six.

Q6. The salts of alkali metals are the most ionic salts known. Although lithium is an alkali yet its compounds, particularly halides, are slightly covalent in nature.

Solution

Li+ ion has small size and has maximum tendency to distort the electron cloud of the anion by withdrawing the electrons from the negative ion towards itself. This tendency to distort the electron cloud of the negative ion by the positive ion is known as polarization.

It causes the charges on the ions to become less since some of their charges get neutralized. This leads to the covalent character of the bond.

The larger the polarization, the larger will be the covalent character of the bond. Thus, Li+ being small in size polarizes the anion and results in a decrease of the positive charge on Li+ ion. Therefore, lithium halides are covalent in nature.

Q7. 

Solution

Q8. Solvay process cannot be used for preparing potassium carbonate. Why?

Solution

Solvay process cannot be used for preparing potassium carbonate because when ammonium hydrogen carbonate is added to a saturated solution of KCl, the potassium hydrogen carbonate formed is soluble and do not precipitate out like sodium hydrogen carbonate.

Q9. What are the features of lithium which separates it from other elements of Group 1?

Solution

The following features separate lithium from the other elements of Group I:

(i) Lithium is the hardest of all the alkali metals.

(ii) The melting and boiling points of lithium are much higher than those of other elements of Group 1.

(iii) Lithium is less reactive as compared to other metals and it does not get tarnished readily in air.

(iv) It forms only monoxide, Li2O with oxygen while sodium forms peroxide-Na2O2; other elements form superoxide, MO2.

(v) Because of high polarizing power of Li+ ion, the salts of lithium have lower ionic character than salts of other alkali metals.

(vi) While other alkali metals do not react with nitrogen, lithium does, forming nitride.

(vii) Only lithium combines with carbon and silicon forming the carbide and the silicide.

(viii) Lithium hydroxide and carbonate are unstable and decompose on heating while the corresponding compounds of the rest of the family members are stable and do not decompose:

(ix) When lithium nitrate is heated it gives nitrogen dioxide and oxygen

(x) Sodium nitrate and potassium nitrate upon strong heating form corresponding nitrites and evolve oxygen.

(xi) Lithium chloride and nitrate are soluble in alcohol, while the salts of sodium are insoluble in alcohol.

(xii) The hydride of lithium (LiH) is more stable as compared to the hydrides of other members of the family.

(xiii) The Li+ ion and its compounds are more heavily hydrated than those of sodium.

(xiv) Lithium hydroxide is much less basic than the hydroxides of other metals.

(xv) Lithium fluoride, carbonate, hydroxide, oxalate are sparingly soluble in water. The corresponding salts of sodium and potassium are readily soluble.

Q10. How will you obtain:

(i) BeCl2 from BeO

(ii) BeH2 from BeCl2 Give reactions only.

Solution

(i)      BeO + C + Cl2BeCl2 + CO

(ii)    2BeCl2 + LiAlH4 2BeH2 + AlCl3 + LiAlH4

Q11. Which of the following is kept under kerosene:

  • 1) Sodium
  • 2) Rubidium
  • 3) Lithium
  • 4) Cesium

Solution

Sodium metal is very reactive.

Q12. Li shows difference in properties than rest of the members of its group but shows similarities with:

  • 1) Mg
  • 2) Al
  • 3) Ca
  • 4) Be

Solution

Due to diagonal relationship, Li resembles Mg.

Q13. Why the hydroxides of alkali and alkaline earth metals are basic in nature? Explain the periodicity of these hydroxides.

Solution

The hydroxides are basic in nature and basic strength increases down the group. This is due to the low ionization energies of these metals where the M-O bond in MOH is weak and it can cleave to give OH ions in solution.

As the ionization energy decreases down the group, the basic strength of the hydroxides increases. For example, Be(OH)2 is amphoteric, Mg(OH)2 is mildly basic while others are strong bases.

Q14. Why are potassium and caesium, rather than lithium used in photoelectric cells?

Solution

Because of low ionization enthalpy of potassium and caesium as compared to lithium, they are able to lose their outermost electron when exposed or irradiated with light. This property makes caesium and potassium useful in photoelectric cells.

Q15. How calcium carbonate can be prepared?

Solution

Calcium carbonate can be prepared by passing carbon dioxide through slaked lime or by adding sodium carbonate to calcium chloride. Ca(OH)2  +  CO CaCO3  + H2O   CaCl2 + Na2CO3  CaCO3 +  2NaCl

Q16. Why is LiF almost insoluble in water whereas LiCl soluble not only in water but also in acetone?

Solution

Due to high lattice enthalpy of LiF as compared to LiCl, LiF is almost insoluble in water. LiCl is soluble in acetone also due to larger anion as compared to cation, polarization occur and thus LiCl posses some covalent character.

Q17. What is baking soda? How is it prepared?

Solution

Baking soda is sodium hydrogen carbonate i.e. NaHCO. When a saturated solution of sodium carbonate is treated with CO2, we get sodium hydrogen carbonate. Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '.

Q18. Why alkali metals are kept in kerosene oil?

Solution

Because of the high reactivity of alkali metals they are kept in kerosene oil.

Q19. 

Solution

Q20. Explain the following

(i) Alkaline earth metals are weaker reducing agent than alkali earth metals.

(ii) Alkaline earth metals have higher melting point than alkali earth metals.

Solution

(i)     The reducing nature is determined by the tendency of losing electron. Since this tendency is lower in alkaline earth metal than alkali metal, the former are weaker reducing agent.

(ii)   Due to the smaller size of alkaline earth metals as compared to alkali metals, alkaline earth metals have higher melting point than alkali earth metals.

Q21. How are magnesium and potassium biologically important?

Solution

Magnesium and potassium ions are found in biological fluids. These ions perform function like maintenance of ion balance and nerve impulse conduction. Enzymes that utilize ATP in phosphate require Mg as the cofactor.

Potassium ions are the most abundant cations within cell fluids. They even participate in the oxidation process of glucose to produce ATP. Sodium and potassium ions are responsible for the transmission of nerve signals. Also Na-K pump operates within the cell membrane.

Q22. When an alkali metal dissolves in liquid ammonia the solution can acquire different colors. Explain the reasons for this type of color change.

Solution

When alkali metals are dissolved in liquid ammonia they give blue colored conducting solution. This solution contains ammoniated electron which absorbs light in the visible region and imparts a blue color to the solution.

This solution is paramagnetic. In the concentrated solution, the blue color changes to bronze color, and the solution becomes diamagnetic.

Q23. Beryllium and magnesium do not give color to flame whereas other alkaline earth metals do so. Why?

Solution

Generally the colour of flame of alkaline metals are due to the  reason that electrons are excited to higher energy levels and when they drop back to the ground state, energy is emitted in the form of visible light.

Since the electrons in beryllium and magnesium are too strongly bound they cannot get excited by flame. Hence Beryllium and magnesium do not give color to a flame.

Q24. Why does lithium show anomalous behavior?

Solution

Lithium differs in many respects from the remaining characteristic properties of the metals of Group 1, due to the following reasons:

a) The size of lithium atom and ion is very small.

b) The polarizing power of Li+ ion is quite high and results in the covalent character of its compounds.

c) It has high ionization energy and least electropositive character.

d) It has no vacant d-orbitals in its valence shell.

Q25. Why Sr(OH)2 and Ba(OH)2 are soluble in water whereas Be(OH)2 and Mg(OH)2  are almost insoluble in water?

Solution

Be(OH)2 and Mg(OH)2 are almost insoluble, Ca(OH)2 is sparingly soluble while Sr(OH)2 and Ba(OH)2 are fairly soluble. This is due to increase in size of the cation and decrease in their lattice energies on moving down the group.

Hydration energies become more due to decrease in lattice energies and so the solubility of hydroxide in water increases. This explains the increasing solubility of alkaline Earth metal hydroxides on moving down the group.

Lattice energy decreases with an increase in the size of the cation and therefore, solubility increases from Be to Ba.

Q26. Discuss any four properties which show the anomalous behavior of Be and its similarity with Al.

Solution

The following points illustrate the anomalous behavior of Be and its resemblance with Al.

(i) Unlike groups – 2 elements but like aluminium, beryllium forms covalent compounds.

(ii) The hydroxides of Be, [Be(OH)2] and aluminium [Al(OH)3] are amphoteric in nature, whereas those of other elements of group – 2 are basic in nature.

(iii) The oxides of both Be and Al i.e. BeO and Al2O3 are high melting insoluble solids.

(iv) BeCl2 and AlCl3 have bridged chloride polymeric structure.

Q27. Why the Mg and Be reacts with air only in powdered state?

Solution

Due to formation of an oxide film on the surface of metal they are unable to react further. Hence powdered metal is used to react with air.

Q28. Give method to prepare beryllium chloride. Deduce the structure of the compound.

Solution

It is prepared by heating beryllium oxide with chlorine vapours in the presence of carbon. Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '. Beryllium chloride has a polymeric chain structure in the soilid state due to its electron deficient nature. It has only four electrons in the valence shell and can accept two electron pairs (from neighbouring Cl atom forming coordinate bonds) to complete its octet. 

Polymeric structure of BeCl2 Each Be atom is tetrahedrally surrounded by four Cl Atoms. Two of the chlorine atoms are bonded by covalent bonds while the other two by coordination bonds.

Q29. What happens when:

(i) Sodium metal is dropped in water.

(ii) Sodium metal is heated in free supply of air.

(iii) Sodium reacts with dihydrogen at 673K.

Solution

(i) Sodium reacts with water to give sodium hydroxide and dihydrogen.      Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '. 

(ii) Sodium form sodium peroxide when heated in free supply of air.      Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '. 

(iii) Sodium forms sodium hydride on reacting with dihydrogen at 673 K.       Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '.    

Q30. MgCl2 and CaCl2 exist as MgCl2.6H2O and CaCl2· 6H2O while NaCl and KCl do not form such hydrates. Why?

Solution

Because the hydration enthalpies of alkaline earth metal ions, they are larger than those of alkali metal ions. Hence, NaCl and KCl do not form such hydrates as MgCl2 and CaCl2.

Q31. What happens when water is added to lime?

Solution

When water is added to lime it forms calcium hydroxide. The process is termed as slaking of lime.   CaO  +   H2O Ca(OH)2

Q32. Why does the solution of alkali metals in ammonia is conducting in nature?

Solution

Alkali metals dissolve in liquid ammonia to give deep blue solutions that are conducting in nature. This happens because the alkali metal atom readily loses the valence electron in the ammonia solution. Both the cation and the electron combine with ammonia to form ammoniated cation and ammoniated electron. 

The ammoniated electron is responsible for the blue color of the solution. The solution is made conducting in nature by both ammoniated cation and ammoniated electron. On standing, the solution slowly liberates hydrogen as: 

Q33. State the common characteristic features of Li and Mg.

Solution

Lithium has a diagonal relationship with magnesium and both have similarities in some of their characteristics.

a) The atomic radius of both elements is close; lithium (152 pm) and magnesium (160 pm).

b) Both have almost similar electronegativities (Li = 1.0, Mg = 1.2)

c) Both Li and Mg are quite hard.

d) Both LiOH and Mg(OH)2 are weak bases.

e) Lithium reacts with N2 to form lithium nitride, while magnesium also reacts in a similar way. Other members of the group do not display this characteristic.

f) Both lithium and magnesium combine with oxygen to form monoxides. Other member form peroxides and superoxides.

g) On strong heating, the hydroxides of both metals decompose to form respective oxides.

h) When heated, the carbonates of both these metals evolve CO2.

i) The nitrates of both lithium and magnesium evolve nitrogen dioxide and oxygen on heating.

j) Lithium hydroxide, fluoride, phosphate, oxalate and carbonate are comparable to those of the corresponding magnesium compounds.

However, the solubilities are much less soluble than the corresponding sodium and potassium salts.