NCERT Class 11 Chemistry Chapter 10 S Block Elements Short Answer Questions

NCERT Solutions For Class 11 Chemistry Chapter 10 S Block Elements Short Question And Answers

Question 1. Li⁺ ion is the smallest one among the ions of group- 1 elements. It would, therefore, be expected to have much higher ionic mobility, and hence the solutions of lithium salts would be expected to have higher conductivity than the solutions of cesium salts. However, in reality, the reverse is observed. Explain
Answer: 

Due to high charge density, very small Li⁺ ion gets much more hydrated compared to the large Cs⁺ ion. Thus, the size of the hydrated lithium-ion is much larger than that of the hydrated cesium ion. For this reason, the mobility of Li⁺ ion is much lower than that of Cs⁺ ion and consequently, the solutions of lithium salts have much lower conductivity than the solutions of cesium salts.

Question 2. The E° value for Cl₂/Cl^– is +1.36, for I₂/I^– is + 0.53V, for Ag⁺/Ag is + 0.79 V, for Na⁺/Na is -2.71V and for Li⁺/Li is -3.04V. Arrange the following atoms and ions in decreasing order of their reducing strength: I^–, Ag, Cl^–, Li, Na
Answer:

The lower the value of standard reduction potential, the greater the tendency of the reduced form to be oxidized, i.e., the reduced form will serve as a stronger reductant. Therefore, the decreasing order of reducing strength of the given atoms and ions is

Li > Na > I^–> Ag > Cl^–

Question 3. The alkali metals are obtained not by the electrolysis of the aqueous solutions of their salts but by the electrolysis of their molten salts. Explain.
Answer:

The solutions of alkali metal salts contain metal cations, anions, H⁺ ions, and OH^– ions. The discharge potential of H⁺ ions is lower than that of metal cations. So, on electrolysis of tire solutions of alkali metal salts, hydrogen is discharged at the cathode rather than the metal. However, when the molten salts of alkali metals are electrolysed, the metal cation being the only cation present, gets discharged at the cathode.

Question 4. The alkali metals are paramagnetic but their salts are diamagnetic—why?
Answer:

Due to the presence of an unpaired valence electron the alkali metals are paramagnetic. During salt formation, this unpaired electron of the outermost shell leaves the metal atom and becomes attached to a non-metal atom. As a result, the cation and the anion thus obtained contain no unpaired electron. Hence, the alkali metal salts are diamagnetic.

Question 5. Beryllium & magnesium do not give color to flame whereas other alkaline earth metals do so. Why?
Answer: 

Due to their smaller size, valence electrons of Be and Mg are more tightly held by the nucleus. Therefore, they need a large amount of energy for the excitation of their valence electrons to higher energy levels. Since such a large amount of energy is not available from Hansen flame, these two metals do not impart any color to the flame.

Question 6. E° for M²⁺(aq) + e →M(s) (where, M = Ca, Sr or Ba) Is nearly constant. Comment.
Answer:

The value of standard electrode potential (E°) of any M²⁺/M electrode depends upon three factors.

1. Enthalpy of vaporisation
2. Ionization enthalpy, and
3. Enthalpy of hydration.

Since the combined effect of these factors is approximately the same for Ca, Sr, and Ba, their standard electrode potential (E°) values are nearly constant.

Question 7. Both alkaline earth metals and their salts are diamagnetic. Explain.
Answer:

The alkaline earth metals are diamagnetic as all the orbitals are filled with paired electrons. The ions of alkaline earth metals, M²⁺ have stable noble gas configurations in which all the orbitals are doubly occupied. Also, there are no unpaired electrons in the anions. Hence, the salts of alkaline earth metals are also diamagnetic.

Question 8. Beryllium salts can never have more than 4 molecules of water of crystallization, i.e., they can never achieve a coordination number > 4 while other metal ions tend to have a coordination number of 6, for example: [Ca(H₂O₆)²⁺. Explain.
Answer: 

Beryllium does not exhibit coordination numbers more than 4 because, in its valence shell of Be²⁺ ion, there are only four available orbitals (one s and three p) present. The remaining members of the group can have a coordination number of six by using their d -d-orbitals along with s -and p -orbitals.

Question 9. Anhydrous is used as a drying agent — why?
Answer:

Anhydrone or magnesium perchlorate, Mg(ClO₄)₂ is  used as a drying agent because, due to its smaller size and higher charge, Mg has a greater tendency to complexation with water molecules by forming Mg(ClO₄)₂ -6H₂O

Question 10. Li salts are commonly hydrated while other alkali metal salts are usually anhydrous. Explain.
Answer:

Due to the smallest size among all alkali metal ions, the Li⁺ ion can interact with water molecules more easily than the other alkali metal ions. Hence the salts of lithium are commonly hydrated. On the other hand, other alkali metal ions being larger have little tendency to get hydrated. Therefore, their salts are generally anhydrous. For example, lithium chloride crystallizes as LiCl. 2H₂O₂ but sodium chloride crystallizes as NaCl.

Question 11. Although the abundance of Na and K in the earth’s crust are comparable, sodium is nearly 30 times more abundant than potassium in seawater—why?
Answer:

These metals were leached from the aluminosilicate rocks by weathering. The potassium salts having large anions are less soluble than the sodium salts because of higher lattice energy. Moreover, potassium is preferentially absorbed by the plants. For this reason, sodium is more abundant than potassium in seawater.

Question 12. When caustic soda solution is kept in a glass bottle, the inner surface of the bottle becomes opaque. Explain
Answer:

Caustic soda (NaOH) being strongly basic reacts with acidic silica (SiO₂) present in glass to form sodium silicate (Na₂SiO₃)

SiO₂ + 2NaOH → Na₂SiO₃ + H₂O

As a result, the inner surface of the bottle becomes opaque.

Question 13. Why are alkali metals stored in kerosene?
Answer:

When the highly reactive alkali metals are exposed to air,  they readily react with oxygen, moisture, and carbon dioxide of air to form oxides, hydroxides, and carbonates respectively. To prevent these reactions, alkali metals are normally stored in kerosene, an inert liquid.

Question 14. The second ionization enthalpies of alkaline earth metals are much lower than those of the corresponding alkali metals. Explain.
Answer:

The loss of a second electron from an alkali metal cation (M⁺) causes a loss of stable noble gas configuration while the loss of a second electron from an alkaline earth metal cation leads to the attainment of a very stable noble gas configuration. This explains why the second ionization enthalpies of alkaline earth metals are much lower than those of the corresponding alkali metals.

Question 15. MgO is used as a refractory material— Explain why
Answer:

Due to greater charge on both the cation (Mg²⁺) and die anion (O^2-), MgO possesses higher lattice energy and for tills, it has a very high melting point and does not decompose on heating. For this reason, it is used as a refractory material

Question 16. BaSO₄ is insoluble in water whereas BeSO₄ is soluble in water—1-explain with reason._
Answer: 

The lattice enthalpy of BaSO₄ is much higher than its hydration enthalpy and hence it is insoluble in water. On the other hand, the hydration enthalpy of BeSO₄ is much higher than its lattice enthalpy because of the loose packing of the small Be²⁺ ion with the relatively large sulfate ion. Hence, it becomes soluble in water.

Question 17. BeCl₂ fumes in moist air but BaCl₂ does not. Explain
Answer:

BeCl₂ being a salt of a weak base, Be(OH)_2, and a strong acid, HCl undergoes hydrolysis in moist air to form HCl; which fumes in air. BaCl₂ on the other hand, being a salt of a strong base, Ba(OH)_2, and a strong acid, HCl does not undergo hydrolysis to form HCl and hence does not fume in moist air

BeCl₂ + 2H₂O→Be(OH)₂ + 2HCl↑

BaCl₂ +H₂O→ Ba(0H)₂ + 2HCl

Question 18. Mg₃N₂ when reacts with water, gives off NH₂ but HCl is not evolved when MgCl₂ reacts with water at room temperature. Give reasons.
Answer:

Mg₃N₂ is a salt of the strong base, Mg(OH)₂ and the weak acid, NH₃

Hence it gets hydrolyzed to give NH₃.

Mg₃N₂ + 6H₂O→ 3Mg(OH)₂ + 2NH₃T↑

MgCl₂,  On the other hand, is a salt of the strong base, Mg(OH)_2, and the strong acid, HCl. Hence, it does not undergo hydrolysis.

Question 19. A piece of burning magnesium ribbon continues to bum in sulfur dioxide.
Answer:

A piece of magnesium ribbon continues to bum in SO₂ since it reacts to form MgO and S. This reaction is such exothermic that heat evolved keeps the magnesium ribbon burning.

This reaction is such exothermic that heat evolved keeps the magnesium ribbon burning.

Question 20. Ba²⁺ ions are poisonous, still, they are provided to patients before taking stomach X-rays. Explain
Answer:

A barium meal (suspension of BaSO₄ in water) is generally given to patients when X-ray photographs of the alimentary canal are required. The salt provides a coating of the alimentary canal and hence X-ray photograph can be taken since it is quite transparent to the X-ray otherwise. BaSO₄ is almost insoluble in water and hence it does not pass from the digestive system to the circulatory system and can therefore be safely used for the purpose.

Question 21. Can sodium hydride be dissolved in water? Justify.
Answer:

Sodium hydride cannot be dissolved in water because it gets hydrolyzed with brisk effervescence of hydrogen gas.

NaH + H₂ O→  H₂ + NaOH

Question 22. Why does sodium impart a yellow color in the flame?
Answer:

The ionization enthalpy of Na is relatively low. Therefore when this metal or its salt is heated in Bunsen flame, its valence shell electron is excited to higher energies by absorption of energy. When the excited electron returns to its initial position in the ground state, it liberates energy in the form of light in the yellow region of the electromagnetic spectrum. That’s why sodium imparts a yellow color to the flame.

Question 23. Wind makes lithium exhibit uncommon properties compared to the rest of the alkali metals.
Answer:

The unusual properties of lithium as compared to other alkali metals are since

• Li – atom and L⁺  ion are exceptionally small in size and
• Li⁺ ion has the highest polarising power (i.e.„ charge/size ratio).

Question 24. What is the common oxidation state exhibited by the alkali metals and why?
Answer:

The alkali metals easily lose their valence electrons (ns¹) to acquire a stable octet, (i.e., the stable electronic configuration of the nearest noble gas) and because of this, the common oxidation state exhibited by the alkali metals is +1.

Question 25. What is the difference between baking soda and baking powder?
Answer:

Both baking soda and baking powder are leavening agents. Baking soda is pure sodium bicarbonate. When baking soda is combined with moisture and an acidic ingredient (for example,  Yoghurt, buttermilk) the resulting chemical reaction produces CO₂ gas bubbles that cause baked goods to rise. Baking powder contains NaHCO₃, but it includes an acidifying agent (cream of tartar) already, and also a drying agent (usually starch).

Baking powder is available as single-acting baking powder and as double-acting baking powder. Single-acting baking powders are activated by moisture, so we must bake recipes that include this product immediately after mixing. Double-acting powder reacts in two phases and can stand for a while before baking.

Question 26. Though table salt is not deliquescent it gets wet ! in the rainy season— Explain.
Answer:

Pure NaCl is not deliquescent but table salt contains impurities like MgCl₂ and CaCl₂ These impurities being deliquescent absorb moisture from air in the rainy season. As a result, table salt gets wet.

Question 27. What precautions should be taken while handling beryllium compounds and why?
Answer:

Contact of Be compounds with skin dermatitis, and inhaling dust or smoke of Be-compounds causes a disease called berylliosis which is rather similar to success- Therefore, beryllium compounds should be handled with care.

Question 28. Explain why the elements of group 2 form M²⁺ Ions, but not M3+ ions.
Answer:

Loss of third electron from group-2 metal atoms causes loss of stable noble gas configuration and for this reason group- 2 elements form M²⁺ ions but not M³⁺ ions. fifl Arrange Be(OH)₂, Ba(OH)₂ & Ca(OH)₂in order of increasing solubility in water and explain the order. Answer: Among the alkaline earth metal hydroxides having a common anion, the cationic radius influences the lattice enthalpy. Since the lattice enthalpy decreases much more than the hydration enthalpy with increasing cationic size, the solubility increases on moving down the group.

Question 29. The reaction between marble and dilute H₂SO₄ is not used to prepare CO₂ gas—why?
Answer:

Marble (CaCO₃) reacts with dilute H₂SO₄ to form insoluble CaSO₄ which deposits on the surface of marble and prevents further reaction. So, the evolution of CO₂ ceases after some time. Thus the reaction between marble and dilute H₂SO₄ prepares CO₂ gas.

Question 30. Name the important compound of Li used in organic synthesis. How the compound is prepared?
Answer:

The compound is lithium aluminum hydride (LiAlH₄). It is a useful reducing agent and is used in organic synthesis. It is prepared by the reaction of lithium hydride and aluminum chloride in a dry ether solution.

4LiH + AlCl₃ → LiAlH₄ + 3LiCl

Question 31. What is the oxidation state of K in KO₂ and why is this compound paramagnetic?
Answer:

The superoxide ion is represented as O^–₂. It has one unit of negative charge. Since the compound is neutral, therefore, the oxidation state of K is +1. The structure of Or is 6J0 O^–₂ Since it has one unpaired electron in π∗_2p MO, therefore, the compound is paramagnetic.

Question 32. The crystalline salts of alkaline earth metals contain more water for crystallization than the corresponding alkali metals. Explain.
Answer:

In the salts of alkaline earth metals, the metal ions have a smaller size and higher charge compared to the corresponding metal ions of the alkali metals of the same period. Thus, alkaline earth metals have a greater tendency to get hydrated & form crystalline salts compared to alkali metals. Thus, NaCl is completely anhydrous whereas MgCl₂ exists as MgCl₂-6H₂O.

Question 33. Lithium salts are more stable if the anion present in the salt is small. Explain.
Answer:

Small anions have more ionic character and hence the salts of lithium containing those ions have more lattice enthalpy. Large anions, on the other hand, are highly polarisable, and hence they impart covalent character to the salt. Thus, lithium salts are more stable with small anions than that with large anions.

Question 34. Alkali metals become opaque when they are kept open in the air Why?
Answer:

As the alkali metals are highly reactive, they readily react 20; with oxygen to form oxides. These oxides undergo a reaction with the water vapor present in the air to produce hydroxides. The formed hydroxides immediately react with CO₂ of air to produce carbonate compounds. These carbonate compounds form layers on the surface of alkali metals. Consequently, they become opaque.

Question 35. BaSO₄ is insoluble in water, but BcSO₄ is soluble in water-Explain.
Answer:

The lattice enthalpy of BaSO₄ is much higher than its hydration enthalpy and hence, it is insoluble in water. On the other hand, the hydration enthalpy of BeSO₄ is much higher than its lattice enthalpy because of the loose packing of the small Be²⁺ ion with the relatively large sulfate ion. Hence, it becomes soluble in water.

Question 36. An aqueous solution of Be(NO₃)₂ is strongly acidic. Explain.
Answer:

In the hydrated ion, [Be(H₂O)₄]²⁺, water molecules are extensively polarised, ultimately leading to the weakening of the O —H bond.

Hydrolysis takes place and the solution becomes distinctly acidic:

(H₂O)₃Be₂ +—OH₂ + H₂O→(H₂O)₃ 3 Be⁺ —OH + H₃O⁺

Question 37. The hydroxides and carbonates of Na and K are readily soluble in water while the corresponding salts of Mg and Ca are sparingly soluble. Explain.
Answer:

Due to smaller size and higher ionic charge, the lattice enthalpies of alkaline earth metals are much higher than those of alkali metals and hence the solubility of alkali metal hydroxides and carbonates is much higher than those of alkaline earth metal hydroxides and carbonates;

Question 38. BeO is insoluble but BeSO₄ is soluble in water. Explain.
Answer:

The higher lattice enthalpy of BeO formed by the combination of a small cation and small anion is more than its hydration enthalpy but the lattice enthalpy of BeSO₄ formed by the combination of a small cation and large anion is less than its hydration enthalpy;

Question 39. BaO is soluble but BaSO₄ is insoluble in water — why?
Answer:

The lattice enthalpy of BaO formed by the combination of a large cation and a small anion is less than its hydration enthalpy but the lattice enthalpy of BaSO₄ formed by the combination of a large cation and a large anion is more than its hydration enthalpy;

Question 40. Lil is more soluble than KIin ethanol. Explain.
Answer:

Due to the much higher polarising power of very small Li⁺ ion, Lil is predominantly covalent but due to the low polarising power of relatively large K⁺ ion, KI is predominantly ionic and for this reason, Lil is more soluble in the organic solvent ethanol;

Question 41. How can fused calcium chloride be prepared? Give two important uses of it.
Answer:

When CaCl₂ 2H₂O is heated above 533K, anhydrous CaCl₂ forms. This melts at 1046K. When the molten salt is cooled, it solidifies as white lumps of crystalline mass which is known as fused calcium chloride;

Question 42. Hydrated magnesium chloride is heated in the presence of ammonium chloride (NH₄Cl).
Answer:

Magnesium chloride when heated with NH₄Cl forms an additional compound (MgCl₂-NH₄Cl₆H₂O) which on heating forms anhydrous MgCl₂

Question 43. Why are alkali metals not found in nature?
Answer:

Alkali metals are highly electropositive and extremely reactive elements. Thus, they easily react with atmospheric oxygen and carbon dioxide. These metals have a high tendency to lose electrons to form cations because of their low ionization potential. For this reason, they readily react with highly electronegative elements or radicals to form compounds. So, alkali metals are not found in a free state in nature.

Question 44. Explain why is sodium less reactive than potassium.
Answer:

Due to its small size, the ionization enthalpy of sodium (496kL-mol^-1) is greater than potassium (419kJ. mol^-1) and the standard electrode potential value of potassium (-2.925V) is more negative than that of sodium (-2.714V). Thus, sodium is less reactive than potassium.

Question 45. Basicity of oxides
Answer:.

Basicity of oxides: The ionization enthalpy of alkali metals is less than that of the corresponding alkaline earth metals, i.e., the electropositive character of alkali metals is greater than that of alkaline earth metals. Thus, the basicity of oxides of alkali metals is more than the oxides of alkaline earth.

NCERT Solutions For Class 11 Chemistry Chapter 10 S Block Elements Warm-Up Exercise Question And Answers

Question 1. Name the lightest and the heaviest metal.
Answer:   Lithium is the lightest (density: 0.53g-cm^-3) and osmium is the heaviest (density: 22.6g-cm^-3 ) metal.

Question 2. Which one between water and pyrene (CCl₄), can be used to extinguish fire caused by metallic sodium?
Answer:  Pyrene (CCl₄) can be used.

Question 3. Which among the alkali metal ions has the lowest mobility In aqueous solution?
Answer: Li⁺ ions have the lowest mobility because they remain highly hydrated in aqueous solution.

Question 4. Which of the alkali metal cations has the highest polarising power?
Answer: Due to its very small size, Li⁺ ion has the highest polarising power among the alkali metal ions

Question 5. The density of alkali metals is very low Why?
Answer: Due to large atomic size and weak metallic bonding, the densities of alkali metals are very low.

Question 6. Name a radioactive alkali metal and write its atomic number.
Answer:  Francium, atomic number =87

Question 7. Mention the similarity shown in the electronic configurations of the alkali metals.
Answer: All alkali metals have similar valence shell electronic configuration of ns¹

Question 8. Why alkali metals are called s -s-block elements?
Answer: Alkali metals are called s -s-block elements because the last electron enters the ns-orbital

Question 9. What is trona?
Answer:

Trona ( Na₂ CO₃ , NaHCO₃  .  2H₂O) is an important mineral of sodium

Question 10. Arrange lithium, sodium, and potassium according to their abundance in the earth’s crust.
Answer:

According to their abundance in nature, the elements are arranged as lithium < potassium < sodium.

Question 11. Give an example of a double salt formed by an alkali metal and alkaline earth metal.
Answer:

The double salt formed by an alkali metal and an alkaline earth metal is carnallite (KCl-MgCl₂-6H₂O)

Question 12. Arrange LiF, NaF, KF, RbF, and CsF in increasing order of their lattice energies.
Answer:

The increasing order of lattice energies of the given compounds is CsF < RbF < KF < NaF < LiF.

Question 13. Why are alkali metals paramagnetic?
Answer: Due to the presence of unpaired electrons in the valence shell of alkali metals, they are paramagnetic.

Question 14. Which alkali metal is generally used in photoelectric cells?
Answer: Cesium is generally used in photoelectric cells

Question 15. Which alkali metals form superoxides when heated in excess air?
Answer: The alkali metals that form superoxides when they are heated in excess air are potassium (K), rubidium (Rb), and cesium (Cs).

Question 16. Differentiate between Na₂CO₃ and NaHCO₃
Answer:

When NaHCO₃ is heated, it liberates CO₂ which turns lime-water milky. On the other hand, when Na₂CO₃ is heated, it does not undergo decomposition

Question 17. Arrange MCI, MBr, MF, and MI (where M= alkali metal) according to increasing covalent character.
Answer:

The covalent character of metallic chlorides increases with an increase in the size of the anion. Therefore, the order of the metallic chlorides according to increasing covalent character is MF < MCI < MBr < MI.

Question 18. Explain why the peroxides and superoxides of the alkali metals act as strong oxidizing agents.
Answer:

In reaction with water, peroxides produce MOH along with H₂O₂ and superoxides produce MOH and O, along with H₂O₂. H₂O₂ is a strong oxidizing agent. Thus, peroxides and superoxides of the alkali metals act as strong oxidizing agents.

M₂O₂ + 2H₂O → 2MOH + H₂O₂

2MO₂ + 2H₂O→ 2MOH + H₂O₂ + O

Question 19. Give a simple test to distinguish between KNO₃ & LiNO₃.
Answer:

Colourless O₂ gas evolves on heating KNO₃. But heating, LiNO₃ dissociates into colorless gas and brown NO₂ gas.

Question 20. Explain why a solution of Na₂CO₃ is alkaline in nature whereas a solution of Na₂SO₄ is neutral.
Answer:

For Na₂CO₃, Na₂SO₄ is a salt of strong base (NaOH) and strong acid (H₂SO₄). So, the nature of the solution of Na₂SO₄ is neutral.

Question 21. Among the sulfate salts of lithium, sodium, potassium, and rubidium, which salt does not form double salt?
Answer: Lithium sulfate (Li₂, SO₄) does not form any double salt

Question 22. What happens when sodium sulfate is fused with charcoal? Give equation.
Answer:

When sodium sulfate is fused with charcoal, it reduces to sodium sulfide, and carbonÿis oxidized to carbon monoxide:

Na₂SO₄ + 4→ Na₂S + 4CO↑

Question 23. Which alkali metal bicarbonate has no existence in the solid state?
Answer:

The alkali metal bicarbonate which has no existence in a solid state is lithium bicarbonate (LiHCO₃)

Question 24. Mention the property for which lithium is used to separate N2 gas from a gas mixture.
Answer:

The alkali metal bicarbonate which has no existence in a solid state is lithium bicarbonate (LiHCO₃)

Question 25. Give a simple test to distinguish between Li₂CO₃ & Na₂CO₃. 
Answer:

On heating, Li₂CO₃ decomposes to CO₂ which turns lime water milky. On the other hand, Na₂ CO₃ does not decompose on heating

Question 26. Write down the name of the alkali metal compound which i

1. Effective in the treatment of manic depressive psychosis
2. Used in baking powder

Answer:

1. Li₂CO₃
2. NaHCO₃

Question 27. Why a standard solution of sodium hydroxide (NaOH) cannot be prepared?
Answer:

Sodium hydroxide, being a hygroscopic substance absorbs moisture from the atmosphere. It also absorbs CO₂ from the air and forms Na₂CO₃. Thus, sodium hydroxide cannot be accurately weighed and so a standard solution of NaOH cannot be prepared.

Question 28. How the group-2 elements are commonly known? Why are they so called?
Answer:

Group-2 elements are commonly known as ‘alkaline earth metals’. These are so-called because their oxides are basic and are found in the earth’s crust.

Question 29. Why group-2 elements are called s -s-block elements?
Answer: Group-2 elements are called s -s-block elements because the last electron enters the s -s-orbital

Question 30. Which group-2 element has a slightly different electronic configuration than the rest of the elements?
Answer:  Beryllium has 2 electrons in its penultimate shell while the rest have 8 electrons in their penultimate shells.

Question 31. Explain why the atomic and ionic radii of Mg are less than those of Na and Ca.
Answer:

The electrons of Mg having a higher nuclear charge are more strongly attracted towards the nucleus. Thus, the atomic and ionic radii of Mg are less than Na. Again on moving down the group (from Mg to Ca), the atomic and ionic radii increase due to the addition of new shells, and the increasing screening effect of joindy overcomes the effect of increasing nuclear charge. Thus, the atomic and ionic radii of Mg are less than Ca.

Question 32. Arrange Mg²⁺, Ba²⁺, Sr²⁺, Be²^+, and Cav according to decreasing order of their hydration enthalpies. Explain your answer.
Answer: The correct order is  → Be²⁺ > Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺

Question 33. Alkaline earth metals predominantly form ionic compounds. However, the first member of the group forms covalent compounds—Explain why.
Answer:

Due to relatively high electronegativity, the first member of each of these groups tends to form covalent compounds.

Question 34. A white residue is obtained when metallic Mg is burnt in air. This residue when heated with water emits an ammoniacal smell. Explain these observations.
Answer:

On burning metallic magnesium in the air, magnesium oxide (MgO) and magnesium nitride (Mg₃N₂) are formed. So, the white residue obtained is a mixture of MgO & Mg₃N₂.

This residue when heated with water, results in the hydrolysis of Mg₃N₂ which emits an ammoniacal smell.

Question 35. Why calcium is better than sodium in eliminating a small amount of water from alcohol?
Answer:

Both Na and Ca react with water to form the corresponding hydroxide. However, sodium rapidly reacts with alcohol to form sodium ethoxide (NaOC₂H₅) but calcium reacts quite slowly with alcohol

2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑

Thus, for eliminating a small amount of water from alcohol, calcium is better than sodium.

Question 36. Why Mg-ribbon continues to burn in the presence of SO₂ gas
Answer:

During the combustion of Mg-ribbon, the amount of heat generated leads to the decomposition of sulfur dioxide into sulfur and oxygen. This oxygen is responsible for the continued burning of Mg-ribbon.

2Mg + SO₂→ 2MgO + S

Question 37. Except Be(OH)₂, all other alkaline earth metal hydroxides are basic and their basic strength increases down the group.
Answer:

Be has high ionization enthalpy, for which Be(OH)₂ is amphoteric.

Question 38. Why is Mg(OH)₂ less basic than NaOH?
Answer:

Due to the larger ionic size and lower ionization enthalpy of Na, the Na — OH bond in NaOH is weaker than the Mg — OH bondin Mg(OH)₂. Thus, NaOH is more basic than Mg(OH)₂

Question 39. Sparingly soluble carbonate salts of alkaline earth metals become easily soluble in water in the presence of CO₂. Why?
Answer:

Sparingly soluble carbonate salts of alkaline earth metals are converted into soluble bicarbonate salts in the presence of CO₂ So, these salts become easily soluble in water.

CaCO₃(s) + CO₂(g) + H₂O(l)→ Ca(HCO₃)₂ (aq)

Question 40. The anhydrous chloride salt of which alkaline earth metal is used as a drying agent in the laboratory?
Answer:

Anhydrous chloride salt of calcium metal, i.e., calcium chloride (CaCl₂) is used as a drying agent in the laboratory.

Question 41. Why BeCO₃ is kept in an atmosphere of CO₂?
Answer:

BeCO₃ being highly unstable easily decomposes to give off CO₂ when kept in an open atmosphere.

Question 42. Write down some important points of difference between beryllium and magnesium.
Answer:

• Beryllium is harder than magnesium,
• Compounds of Be are largely covalent, whereas most of the compounds of Mg are ionic,
• Be does not exhibit a coordination number of more than 4, while Mg exhibits a coordination number of 6

Question 43. Be usually forms covalent compounds but other elements of group ionic compounds. Why?
Answer:

Be usually forms covalent compounds due to its high ionisation enthalpy and small size. However, due to comparatively low ionization enthalpy and large size, other elements of group-2 form ionic compounds

Question 44. Which compounds of the alkaline earth metals are used as refractory substances?
Answer:

The oxides of alkaline earth metals (MO) have high melting points and so are used as refractory substances.

Question 45. Carbonaceous impurities in gypsum and any fuel are avoided during the preparation of Plaster of Paris. Explain.
Answer:

Carbonaceous impurities in gypsum and any fuel are avoided during the preparation of Plaster of Paris because carbon will reduce CaSO₄ to CaS.

CaSO₄ + 4C →  CaS + 4CO ↑

Question 46. The fire caused by sodium in the laboratory cannot be extinguished by spraying water Why?
Answer:

Sodium reacts vigorously with water producing H₂ gas which catches fire by the heat evolved in the reaction. So water cannot be used for extinguishing sodium-fire

Question 47. Why does Li not exist with Na or K in their minerals?
Answer:

Lithium forms independent minerals and does not exist with Na or K because the Li⁺ ion is too small to replace the more abundant Na+ or K⁺ ions in their minerals.

Question 48. How can you prepare propyne from magnesium carbide?
Answer:

When magnesium carbide (MgC₂) is heated, Mg₂C₃ (magnesium allylide) is obtained. This on hydrolysis, produces propyne (CH₃C=CH)

Question 49. Why do halides of Be dissolve in organic solvents while those of Ba do not?
Answer:

Halides of Be are covalent. Hence, they dissolve in organic solvents while Ba is ionic. Hence, they do not dissolve in organic solvents.

Question 50. Write with a balanced equation the reaction for the manufacture of sodium bicarbonate from sodium carbonate.
Answer:

Sodium bicarbonate (NaHCO₃) Is manufactured by passing CO2 through a saturated solution of sodium carbonate (Na₂CO₃).

Na₂CO₃ + CO₂ + H₂O ⇌ 2NaHCO₃↓

Question 51. Write the balanced equation(s) for the reaction when excess carbon dioxide is passed through brine saturated with ammonia
Answer:

When carbon dioxide is passed through an aqueous solution of NaCI (brine, 28% NaCl solution) saturated with ammonia, sodium bicarbonate is formed.

Question 52. Why is LiCl soluble in organic solvents?
Answer:

As the polarising power of Li⁺ is very high, LiCl is covalent. Hence, it is soluble in an organic solvent.

Question 53. Explain why can alkali and alkaline earth metals not be obtained by chemical reduction methods.
Answer:

Alkali and alkaline earth metals are strong, reducing agents and it is difficult to reduce their oxides or chlorides by any other reducing agent.

Question 54. With the help of a drop of an indicator solution, how would you know whether a solution consists of Na₂CO₃ or NaHCO₃?
Answer:

A drop of phenolphthalein will change the colorless solution of Na₂CO₃ to purple but the colorless solution of NaHCO₃ will remain unchanged;

Question 55. The crystalline salts of alkaline earth metals contain more water of crystallization than the corresponding alkali metal salts—why?
Answer:

Due to their smaller size and higher charge, the alkaline earth metal ions have a greater tendency to coordinate with water molecules as compared to alkali metal ions.

Question 56. Beryllium chloride hydrate loses no water over P₄O₁₀ — why?
Answer:

Due to very small size and stronger hydrating tendency of Be²⁺ ion, it is not possible for P₄O₁₀ to abstract water molecules from beryllium chloride hydrate, [Be(H₂O)4]Cl₂;

Question 57. Why are fumes seen when barium halides are kepi In open air?
Answer:

In the open air, barium halide undergoes hydrolysis by water vapor (moisture), and fumes of halogen acid (except HF) evolve.

Question 58. Explain why the compounds of beryllium are much more covalent than the other Gr-2 metal compounds.
Answer:

Due to the very small size and high charge of Be²⁺ ion, it has much higher polarising power and because of this, the compounds of Be are much more covalent than the other group-2 metal compounds.

Question 59. Beryllium compounds are extremely toxic why?
Answer:

Beryllium compounds are extremely toxic because of their very high solubility and their ability to form complexes with enzymes in the body.  Also, beryllium displaces magnesium from some enzymes.

Question 60. Which calcium salt causes the formation of the kidney? Stones?
Answer:

Calcium oxalate, \(\mathrm{Ca}^2+\stackrel{\ominus}{\mathrm{O}}_2 \mathrm{C}-\mathrm{C} \stackrel{\ominus}{\mathrm{O}}_2\) causes formation of kidney stones

Question 61. Alkali metals are good reducing agents—Why?
Answer: 

The smaller the ionization enthalpy, the greater the reducing strength. Since alkali metals have lower ionization enthalpies, they are good reducing agents.

Question 62. Explain why the alkali metals cannot be obtained by the reduction method.
Answer: Alkali metals are strong reducing agents and it is difficult to reduce their oxide with any other reducing agent

Question 63. Which alkali metal ion has the maximum polarising j power and why?
Answer:  Li⁺ ion has the highest polarising power among all the alkali metal ions as the value of charge to size ratio of the smallest Li+ ion is the highest.