Important Questions for CBSE Class 11 Chemistry Chapter 10 - The s-Block Elements

Very Short Answer Questions (1 Mark)

1. Why are Group I elements known as the most electropositive element?

Ans: These elements have the most electropositive metals due to the loosely held s-electron in the outermost valence shell. They rapidly give up an electron, resulting in monovalent \[{{\text{M}}^{\text{+}}}\] ions.

2. Why are lithium salts mostly hydrated?

Ans: Among all alkali metals, lithium is recognised to have the lowest size. The capacity of the lithium-ion to polarise water molecules more easily than other alkali metals is due to this property. Hence,  $\text{L}{{\text{i}}^{\text{+}}}$ ions possess the highest degree of hydration, lithium salts, such as lithium chloride ($\text{LiCl}$) and $\text{2}{{\text{H}}_{\text{2}}}\text{O}$, are predominantly hydrated.

3. Why are melting and boiling points of alkali metals low?

Ans: As the atomic size of alkali metals is bigger and they have only one valence electron, their melting and boiling temperatures are low, indicating weak metallic bonding.

4. What do you mean by the diagonal relationship in the periodic table?

Ans: The diagonal link is owing to the elements' having similar ionic sizes and/or charge/radius ratio.

5. Why is lithium kept under kerosene oil?

Ans: Lithium is kept under kerosene oil because of its strong reactivity to oxygen and water.

6. Name the lightest metal.

Ans: With the density of $0.543\text{g/c}{{\text{m}}^{\text{3}}}$ , lithium is known as the lightest metal on earth. 

7. Why do alkali metal hydroxides make the strongest bases?

Ans: As the alkali metal hydroxides dissolve freely in water and generate a lot of heat due to high hydration, they are known as the most powerful of all bases.

8. Why are peroxides and superoxides stable in comparison to other oxides?

Ans: Peroxides and superoxides are stable because larger anions are stabilised by larger cations through lattice energy effects.

9. Name the anomalous properties of lithium.

Ans: The anomalous properties of lithium are as follows:

1. The lithium-ion ($\text{L}{{\text{i}}^{\text{+}}}$) is of exceptionally small size.

2. The charge by radius ratio, also called the polarizing power of lithium high.

10. Why are lithium compounds soluble in organic solvents?

Ans: Due to high polarizing power, there is an increased covalent character of lithium compounds which is responsible for their solubility in organic solvents.

11. How is sodium carbonate prepared?

Ans: Sodium carbonate is generally prepared by Solvay’s process. Solvay’s process is an industrial process for obtaining sodium carbonate from limestone, ammonia and brine.

12. What is sodium amalgam?

Ans: Sodium amalgam is formed when sodium metal discharged at the cathode reacts with mercury. 

13. Why is sodium hydrogen carbonate known as baking powder?

Ans: Sodium hydrogen carbonate is known as baking soda because it decomposes on heating and generates bubbles of carbon dioxide gas ($\text{C}{{\text{O}}_{\text{2}}}$) which leaves holes in cakes and bread.

14. Why does table salt get wet in the rainy season?

Ans: Table salts contain impurities such as $\text{CaC}{{\text{l}}_{\text{2}}}$ and $\text{MgC}{{\text{l}}_{\text{2}}}$ , both of which are deliquescent chemicals that absorb moisture from the air when it rains.

15. What is the formula of soda ash?

Ans: Soda ash also known as sodium carbonate is prepared in large quantities by Solvay process. Its formula is $\text{N}{{\text{a}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}$ . 

16. Why do alkaline earth metals have low ionization enthalpy?

Ans: Due to the huge size of their atoms, alkaline earth metals have low ionisation enthalpies.

17. State one reason for alkaline earth metals, in general, having a greater tendency to form complexes than alkali metals.

Ans: Alkaline earth metals have a tendency to form complexes due to their small size and high charge.

18. Compounds of alkaline earth metals are more extensively hydrated than those of alkali metals. Give a reason.

Ans: Because alkaline earth metals have a lower size than alkali metals, their hydration enthalpies will be higher. As a result, compounds made from alkaline earth metals are more hydrated than those made from alkali metals.

19. The melting and boiling points of alkaline metals are higher than alkali metals. Give a reason.

Ans: Because of their smaller sizes, alkaline metals have greater melting and boiling points than their alkali counterparts.

20. What is the nature of oxide formed by beryllium?

Ans: The oxide formed from beryllium is beryllium oxide ($\text{BeO}$) which is covalent and amphoteric in nature. Whereas, the oxides formed from other elements are ionic and basic in nature. 

21. Why does beryllium show similarities with aluminium?

Ans: The ratio of charge by radium is the same for both beryllium and aluminium, that’s why they both depict similarities.

The charge by radius ratio of beryllium ion is $\text{B}{{\text{e}}^{2+}}=\dfrac{2}{31}=0.064$ and that of aluminum ion is $\text{A}{{\text{l}}^{3+}}=\dfrac{3}{50}=0.66$.

22. Why is beryllium carbonate unusually unstable thermally as compared to the other carbonates of this group?

Ans: This is due to strong polarizing effect of small $\text{B}{{\text{e}}^{\text{2+}}}$ on the large $\text{C}{{\text{O}}_{\text{3}}}^{2-}$  anion and leading to the formation of more stable $\text{BeO}$ .

23. Why are sulphates of $\text{Mg}$ and $\text{Be}$ soluble in water?

Ans: The greater hydration enthalpies of $\text{B}{{\text{e}}^{\text{2+}}}$ and $\text{M}{{\text{g}}^{\text{2+}}}$ ions overcome the lattice enthalpy factor and therefore their sulphates are soluble in water.

24. Why is beryllium not attacked by an acid easily?

Ans: Due to the presence of an oxide film on the beryllium metal, acids are less likely to damage it.

25. Mention the main compounds which constitute Portland cement.

Ans: The main compounds present in Portland cement are- $26%$ of dicalcium silicate  $(\text{C}{{\text{a}}_{\text{2}}}\text{Si}{{\text{O}}_{4}})$ , $51%$  of tricalcium silicate $(\text{C}{{\text{a}}_{\text{3}}}\text{Si}{{\text{O}}_{5}})$ and $11%$ of tricalcium aluminate $(\text{C}{{\text{a}}_{\text{3}}}\text{A}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{5}}})$.

26. What happens when gypsum is heated to $390\text{K}$?

Ans: When gypsum is heated to $390\text{K}$, a compound called calcium sulphate hemihydrates also known as plaster of Paris is formed.

$\text{2CaS}{{\text{O}}_{\text{4}}}\text{.2}{{\text{H}}_{\text{2}}}\text{O}\xrightarrow{390K}{{\text{(CaS}{{\text{O}}_{\text{4}}}\text{)}}_{\text{2}}}{{\text{H}}_{\text{2}}}\text{O}+\text{3}{{\text{H}}_{\text{2}}}\text{O}$ 

27. Anhydrous calcium sulphate cannot be used as plaster of Paris. Give a reason.

Ans:  The anhydrous calcium sulphate is used as a drying agent by readily taking up water. It cannot replace the plaster of Paris because it does not have the same setting and hardening property.

28. Mention the natural sources of calcium carbonate.

Ans: Calcium carbonate can be found in a variety of forms in nature, including limestone, chalk, and marble.

29. What is lime milk of lime?

Ans: The term "milk of lime" refers to a slaked lime suspension in water.

30. What happens when $\text{CaC}{{\text{O}}_{\text{3}}}$ is subjected to heat?

Ans: Calcium carbonate $\text{(CaC}{{\text{O}}_{\text{3}}})$when heated produces calcium oxide also called quicklime with carbon dioxide gas. 

$\text{CaC}{{\text{O}}_{\text{3}}}\rightleftharpoons \text{CaO}+\text{C}{{\text{O}}_{\text{2}}}$ 

31. Show with an example that $\text{CaO}$ is a basic oxide?

Ans: When calcium oxide ($\text{CaO}$) reacts with an acidic oxide at high temperature, it yields salt. 

$\text{6CaO}+{{\text{P}}_{\text{4}}}{{\text{O}}_{\text{10}}}\to 2\text{C}{{\text{a}}_{\text{3}}}{{\text{(P}{{\text{O}}_{\text{4}}}\text{)}}_{\text{2}}}$

$\text{CaO}+\text{Si}{{\text{O}}_{2}}\to \text{CaSi}{{\text{O}}_{\text{3}}}$

Short Answer Questions (2 Marks)

1. Why are lithium halides covalent in nature?

Ans: Lithium halides are covalent in nature because of their high polarisation capability. The $\text{L}{{\text{i}}^{\text{+}}}$ ion is relatively tiny and has a significant tendency to deform the electron cloud surrounding the negative halide ion.

2. What makes lithium show properties different from the rest of the alkali metals?

Ans: Lithium is a small atom and it forms smaller $\text{L}{{\text{i}}^{\text{+}}}$. As a result, it has a very high charge to radius ratio. This is primarily responsible for the anomalous behaviour of lithium.

3. Why do alkali metals and salts impart colour to an oxidizing flame?

Ans: A colour is imparted to the oxidizing flame by alkali metals and salts because the heat from the flame excites the outer orbital electron to a higher energy level.

4. What type of oxide is made of sodium?

Ans: When sodium reacts with oxygen gas, an oxide known as sodium peroxide ($\text{N}{{\text{a}}_{\text{2}}}{{\text{O}}_{\text{2}}}$) is obtained.

$2\text{Na}+{{\text{O}}_{\text{2}}}\to \text{N}{{\text{a}}_{\text{2}}}{{\text{O}}_{\text{2}}}$ 

5. Why is potassium lighter than sodium?

Ans: Potassium is lighter than sodium due to an unusual increase in potassium's atomic size.

6. Name the alkali metals that form superoxides when heated in excess of air.

Ans: The alkali metals that form superoxides when heated with excess air are: potassium, rubidium and caesium.

7. Write a reaction to show that bigger cations stabilize bigger anions.

Ans: The reaction in which bigger cations stabilizes bigger anions is:

$\text{LiI}+\text{KF}\to \text{LiF}+\text{KI}$ 

In the above reaction the bigger cation is${{\text{K}}^{\text{+}}}$ which stabilizes the bigger anion${{\text{I}}^{-}}$. 

8. Lithium shows similarities with magnesium in its chemical behaviour. What is the cause of these similarities?

Ans: The cause of the similarities in the chemical behaviour of lithium and magnesium are:

1. The atomic size of both lithium and magnesium is the same.

2. The charge to size ratio of lithium and magnesium is also the same. 

9. Why metals like potassium and sodium cannot be extracted by reduction of their oxides by carbon?

Ans: Potassium and sodium are both strong electropositive metals with a much higher affinity for oxygen than carbon. As a result, carbon reduction cannot be used to remove them from their oxides.

10. Give the important uses of sodium carbonate.

Ans: The important uses of sodium carbonate are:

1. Sodium carbonate is used in softening, laundering and cleaning.

2. Sodium carbonate is also used in the industrial manufacturing of glass, soap, borax and caustic soda.

11. What is the difference between baking soda and baking powder?

Ans: Baking soda is sodium bicarbonate$\text{(NaHC}{{\text{O}}_{\text{3}}})$. While baking powder is a mixture of sodium bicarbonate and potassium hydrogen tartrate.

12. Discuss the various reactions that occur in the Solvay process.

Ans: Solvay’s process is an industrial process for the manufacturing of sodium carbonate from ammonia, limestone and brine. Following are the various steps that occur in Solvay process:

$2\text{N}{{\text{H}}_{3}}+{{\text{H}}_{2}}\text{O}+\text{C}{{\text{O}}_{2}}\to \left( \text{N}{{\text{H}}_{4}} \right)\text{C}{{\text{O}}_{3}}$

$\left( \text{N}{{\text{H}}_{4}} \right)\text{C}{{\text{O}}_{3}}+\text{C}{{\text{O}}_{2}}+{{\text{H}}_{2}}\text{O}\to 2\text{N}{{\text{H}}_{4}}\text{CH}{{\text{O}}_{3}}$

$\text{N}{{\text{H}}_{4}}\text{HC}{{\text{O}}_{3}}+\text{NaCl}\to \text{N}{{\text{H}}_{4}}\text{Cl}+\text{NaHC}{{\text{O}}_{3}}$

$2\text{NaHC}{{\text{O}}_{3}}\to \text{N}{{\text{a}}_{2}}\text{C}{{\text{O}}_{3}}+\text{C}{{\text{O}}_{2}}+{{\text{H}}_{2}}\text{O}$

13. Give two uses of sodium carbonate.

Ans: Sodium carbonate has two applications:  

1. It is used in the production of soap, glass, paper, borax, and caustic soda, among other things.

2. It is used in both the textile and petroleum refining industries.

14. Solution of sodium carbonate is alkaline. Give a reason.

Ans: The solution of sodium carbonate is alkaline in nature because when sodium carbonate is treated with water, it gets hydrolyzed to form an alkaline solution. 

$\text{N}{{\text{a}}_{2}}\text{C}{{\text{O}}_{3}}(~\text{s})+{{\text{H}}_{2}}\text{O}(\text{I})\to \underset{\text{ Strong base }}{\mathop{2\text{NaOH}(\text{aq})}}\,+\underset{\text{ Weak acid }}{\mathop{{{\text{H}}_{2}}\text{C}{{\text{O}}_{3}}(\text{aq})}}\,$

15. Name the elements present in Group 2.

Ans: The elements present in group 2 of the periodic table are: Beryllium, Magnesium, Calcium, Strontium, Barium and Radium.

16. The atomic radii of alkaline earth metals are smaller than those of the corresponding alkali metals. Explain why?

Ans: Due to an increase in the nuclear charge of the components, the atomic and ionic radii of the alkaline earth metals are smaller than those of the comparable alkali metals in the same period.

17. The second ionization enthalpy of calcium is more than the first. How does that calcium form$\text{CaC}{{\text{l}}_{\text{2}}}$and not$\text{CaCl}$give reasons.

Ans: The higher value of second ionization enthalpy is more than compensated by the higher enthalpy of hydration of$\text{C}{{\text{a}}^{\text{2+}}}$. Therefore the formation of$\text{CaC}{{\text{l}}_{\text{2}}}$becomes more favourable than$\text{CaCl}$energetically. 

18. Name the metal amongst alkaline earth metals whose salt does not impart colour to a non-luminous flame.

Ans: Amongst the elements present in the alkaline earth metals, the metal whose salt does not give colour to a non-luminous flame is beryllium.

19. Which member of the alkaline earth metals family has:

(i)  Least reactivity

(ii) Lowest density

(iii) Highest boiling point

(iv) Maximum reduction potential

Ans: The members of the alkaline earth metals family having the given properties

are:

(i) Least reactivity: Beryllium is the least reactive among the alkaline earth metals.

(ii) Lowest density: Amongst the alkaline earth metals calcium has the lowest density.

(iii) Highest boiling point: Beryllium is the only metal having the highest boiling point amongst the alkaline earth metals.

(iv) Maximum reduction potential: The only metal amongst the alkaline earth metals having the maximum reduction potential is beryllium.

20. The alkaline earth metals are called s – block elements. Give reasons.

Ans: As the last electron in their electrical configuration occupies the s –orbital of their valence shells, alkaline earth metals are known as s –block elements.

21. Why is Calcium preferred over sodium to remove the last traces of moisture from alcohol?

Ans: Both sodium and calcium form hydroxides when they react with water. Calcium, on the other hand, does not react with alcohol to generate sodium alkoxide.

22. Name the metal amongst alkaline earth metals whose salt do not impart colour to a non – luminous flame.

Ans: Amongst the elements present in the alkaline earth metals, the metal whose salt does not give colour to a non-luminous flame is beryllium.

23. Give the reaction of magnesium with air?

Ans: Magnesium reacts with oxygen present in the air and it produces a bright light. The production of bright light is because the reaction is an exothermic reaction and releases a lot of heat. As a result of an exothermic reaction, magnesium oxide is formed as two electrons are donated to the oxygen atom.

${\text{3Mg}} + {{\text{N}}_{\text{2}}} \to {\text{M}}{{\text{g}}_{\text{3}}}{{\text{N}}_{\text{2}}}$

$2{\text{Mg}} + {{\text{O}}_{\text{2}}} \to 2{\text{MgO}}$

24. Beryllium is reducing in nature. Why?

Ans: The significant hydration energy associated with the tiny size of the beryllium ion and the comparatively large value of the metal's atomization enthalpy contributes to the metal's reducing tendency.

25. Give two uses of:

(i) Caustic soda

Ans: Uses of Caustic Soda:

a. It is utilized in the production of soap, paper, synthetic silk, and a variety of chemicals.

b. It is utilized in petroleum refining and bauxite purification.

(ii) Quick Lime:

Ans: Uses of Quick Lime: 

a. It is utilized in the production of dyeing materials.

b. It aids in the production of sodium carbonate from caustic soda.

26. What is quicklime? What happens when we add water to it?

Ans: Calcium oxide, known as quicklime, is an oxide of calcium. Slaked lime is created when water is introduced to quick lime.

$\text{CaO}(s)+{{\text{H}}_{\text{2}}}\text{O}(l)\to \text{Ca(OH}{{\text{)}}_{\text{2}}}$ 

27. What is the formula of caustic potash?

Ans: Caustic potash also known as potassium hydroxide is an inorganic compound with a formula of $\text{KOH}$.

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