Unit 10

The S-Block Elements

I. Multiple Choice Questions (Type-I)

1. The alkali metals are low melting. Which of the following alkali metal is expected to melt if the room temperature rises to $30^{\circ} C$ ?

(i) $Na$

(ii) $K$

(iii) $Rb$

(iv) $Cs$

2. Alkali metals react with water vigorously to form hydroxides and dihydrogen.

Which of the following alkali metals reacts with water least vigorously?

(i) $Li$

(ii) $Na$

(iii) $K$

(iv) $Cs$

3. The reducing power of a metal depends on various factors. Suggest the factor which makes $Li$, the strongest reducing agent in aqueous solution.

(i) Sublimation enthalpy

(ii) Ionisation enthalpy

(iii) Hydration enthalpy

(iv) Electron-gain enthalpy

4. Metal carbonates decompose on heating to give metal oxide and carbon dioxide. Which of the metal carbonates is most stable thermally?

(i) $MgCO_3$

(ii) $CaCO_3$

(iii) $SrCO_3$

(iv) $BaCO_3$

5. Which of the carbonates given below is unstable in air and is kept in $CO_2$ atmosphere to avoid decomposition.

(i) $BeCO_3$

(ii) $MgCO_3$

(iii) $CaCO_3$

(iv) $BaCO_3$

6. Metals form basic hydroxides. Which of the following metal hydroxide is the least basic?

(i) $Mg(OH)_2$

(ii) $Ca(OH)_2$

(iii) $Sr(OH)_2$

(iv) $Ba(OH)_2$

7. Some of the Group 2 metal halides are covalent and soluble in organic solvents. Among the following metal halides, the one which is soluble in ethanol is

(i) $BeCl_2$

(ii) $MgCl_2$

(iii) $CaCl_2$

(iv) $SrCl_2$

8. The order of decreasing ionisation enthalpy in alkali metals is

(i) $Na>Li>K>Rb$

(ii) $Rb<Na<K<Li$

(iii) $Li>Na>K>Rb$

(iv) $K<Li<Na<Rb$

9. The solubility of metal halides depends on their nature, lattice enthalpy and hydration enthalpy of the individual ions. Amongst fluorides of alkali metals, the lowest solubility of $LiF$ in water is due to

(i) Ionic nature of lithium fluoride

(ii) High lattice enthalpy

(iii) High hydration enthalpy for lithium ion.

(iv) Low ionisation enthalpy of lithium atom

10. Amphoteric hydroxides react with both alkalies and acids. Which of the following Group 2 metal hydroxides is soluble in sodium hydroxide?

(i) $Be(OH)_2$

(ii) $Mg(OH)_2$

(iii) $Ca(OH)_2$

(iv) $Ba(OH)_2$

11. In the synthesis of sodium carbonate, the recovery of ammonia is done by treating $NH_4 Cl$ with $Ca(OH)_2$. The by-product obtained in this process is

(i) $CaCl_2$

(ii) $NaCl$

(iii) $NaOH$

(iv) $NaHCO_3$

12. When sodium is dissolved in liquid ammonia, a solution of deep blue colour is obtained. The colour of the solution is due to

(i) ammoniated electron

(ii) sodium ion

(iii) sodium amide

(iv) ammoniated sodium ion

13. By adding gypsum to cement

(i) setting time of cement becomes less.

(ii) setting time of cement increases.

(iii) colour of cement becomes light.

(iv) shining surface is obtained.

14. Dead burnt plaster is

(i) $CaSO_4$

(ii) $CaSO_4 \cdot \frac{1}{2} H_2 O$

(iii) $CaSO_4 \cdot H_2 O$

(iv) $CaSO_4 \cdot 2 H_2 O$

15. Suspension of slaked lime in water is known as

(i) lime water

(ii) quick lime

(iii) milk of lime

(iv) aqueous solution of slaked lime

16. Which of the following elements does not form hydride by direct heating with dihydrogen?

(i) $Be$

(ii) $Mg$

(iii) $Sr$

(iv) $Ba$

17. The formula of soda ash is

(i) $Na_2 CO_3 \cdot 10 H_2 O$

(ii) $Na_2 CO_3 \cdot 2 H_2 O$

(iii) $Na_2 CO_3 \cdot H_2 O$

(iv) $Na_2 CO_3$

18. A substance which gives brick red flame and breaks down on heating to give oxygen and a brown gas is

(i) Magnesium nitrate

(ii) Calcium nitrate

(iii) Barium nitrate

(iv) Strontium nitrate

19. Which of the following statements is true about $Ca(OH)_2$ ?

(i) It is used in the preparation of bleaching powder

(ii) It is a light blue solid

(iii) It does not possess disinfectant property.

(iv) It is used in the manufacture of cement.

20. A chemical $\mathbf{A}$ is used for the preparation of washing soda to recover ammonia. When $CO_2$ is bubbled through an aqueous solution of $\mathbf{A}$, the solution turns milky. It is used in white washing due to disinfectant nature. What is the chemical formula of $\mathbf{A}$ ?

(i) $Ca(HCO_3)_2$

(ii) $CaO$

(iii) $Ca(OH)_2$

(iv) $CaCO_3$

21. Dehydration of hydrates of halides of calcium, barium and strontium i.e., $CaCl_2 6 H_2 O, BaCl_2 \cdot 2 H_2 O, SrCl_2 \cdot 2 H_2 O$, can be achieved by heating. These become wet on keeping in air. Which of the following statements is correct about these halides?

(i) act as dehydrating agent

(ii) can absorb moisture from air

(iii) Tendency to form hydrate decreases from calcium to barium

(iv) All of the above

II. Multiple Choice Questions (Type-II)

In the following questions two or more options may be correct.

22. Metallic elements are described by their standard electrode potential, fusion enthalpy, atomic size, etc. The alkali metals are characterised by which of the following properties?

(i) High boiling point

(ii) High negative standard electrode potential

(iii) High density

(iv) Large atomic size

23. Several sodium compounds find use in industries. Which of the following compounds are used for textile industry?

(i) $Na_2 CO_3$

(ii) $NaHCO_3$

(iii) $NaOH$

(iv) $NaCl$

24. Which of the following compounds are readily soluble in water?

(i) $BeSO_4$

(ii) $MgSO_4$

(iii) $BaSO_4$

(iv) $SrSO_4$

25. When Zeolite, which is hydrated sodium aluminium silicate is treated with hard water, the sodium ions are exchanged with which of the following ion(s)?

(i) $H^{+}$ions

(ii) $Mg^{2+}$ ions

(iii) $Ca^{2+}$ ions

(iv) $SO_4^{2-}$ ions

26. Identify the correct formula of halides of alkaline earth metals from the following.

(i) $BaCl_2 \cdot 2 H_2 O$

(ii) $BaCl_2 \cdot 4 H_2 O$

(iii) $CaCl_2 \cdot 6 H_2 O$

(iv) $SrCl_2 \cdot 4 H_2 O$

27. Choose the correct statements from the following.

(i) Beryllium is not readily attacked by acids because of the presence of an oxide film on the surface of the metal.

(ii) Beryllium sulphate is readily soluble in water as the greater hydration enthalpy of $Be^{2+}$ overcomes the lattice enthalpy factor.

(iii) Beryllium exhibits coordination number more than four.

(iv) Beryllium oxide is purely acidic in nature.

28. Which of the following are the correct reasons for anomalous behaviour of lithium?

(i) Exceptionally small size of its atom

(ii) Its high polarising power

(iii) It has high degree of hydration

(iv) Exceptionally low ionisation enthalpy

III. Short Answer Type

29. How do you account for the strong reducing power of lithium in aqueous solution?

30. When heated in air, the alkali metals form various oxides. Mention the oxides formed by $Li$, $Na$ and $K$.

31. Complete the following reactions

(i) $O_2^{2-}+H_2 O \longrightarrow$

(ii) $O_2^{-}+H_2 O \longrightarrow$

32. Lithium resembles magnesium in some of its properties. Mention two such properties and give reasons for this resemblance.

33. Name an element from Group 2 which forms an amphoteric oxide and a water soluble sulphate.

34. Discuss the trend of the following:

(i) Thermal stability of carbonates of Group 2 elements.

(ii) The solubility and the nature of oxides of Group 2 elements.

35. Why are $BeSO_4$ and $MgSO_4$ readily soluble in water while $CaSO_4, SrSO_4$ and $BaSO_4$ are insoluble?

36. All compounds of alkali metals are easily soluble in water but lithium compounds are more soluble in organic solvents. Explain.

37. In the Solvay process, can we obtain sodium carbonate directly by treating the solution containing $(NH_4)_2 CO_3$ with sodium chloride? Explain.

38. Write Lewis strucure of $O_2^{-}$ion and find out oxidation state of each oxygen atom? What is the average oxidation state of oxygen in this ion?

39. Why do beryllium and magnesium not impart colour to the flame in the flame test?

40. What is the structure of $BeCl_2$ molecule in gaseous and solid state?

IV. Matching Type

In the following questions more than one option of column I and II may be correlated.

41. Match the elements given in Column I with the properties mentioned in Column II.

42. Match the compounds given in Column I with their uses mentioned in Column II.

43. Match the elements given in Column I with the colour they impart to the flame given in Column II.

V. Assertion and Reason Type

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

44. Assertion (A): The carbonate of lithium decomposes easily on heating to form lithium oxide and $CO_2$.

Reason (R) : Lithium being very small in size polarises large carbonate ion leading to the formation of more stable $Li_2 O$ and $CO_2$.

(i) Both $A$ and $R$ are correct and $R$ is the correct explanation of $A$.

(ii) Both $A$ and $R$ are correct but $R$ is not the correct explanation of $A$.

(iii) Both $A$ and $R$ are not correct

(iv) $A$ is not correct but $R$ is correct.

45. Assertion (A): Beryllium carbonate is kept in the atmosphere of carbon dioxide.

Reason (R) : Beryllium carbonate is unstable and decomposes to give beryllium oxide and carbon dioxide.

(i) Both $A$ and $R$ are correct and $R$ is the correct explanation of $A$.

(ii) Both $A$ and $R$ are correct but $R$ is not the correct explanation of $A$.

(iii) Both $A$ and $R$ are not correct.

(iv) $A$ is not correct but $R$ is correct.

VI. Long Answer Type

46. 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.

47. 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

48. 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.

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

50. 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.

51. 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.

52. An element of group 2 forms covalent oxide which is amphoteric in nature and dissolves in water to give an amphoteric hydroxide. Identify the element and write chemical reactions of the hydroxide of the element with an alkali and an acid.

53. Ions of an element of group 1 participate in the transmission of nerve signals and transport of sugars and aminoacids into cells. This element imparts yellow colour to the flame in flame test and forms an oxide and a peroxide with oxygen. Identify the element and write chemical reaction to show the formation of its peroxide. Why does the element impart colour to the flame?

I. Multiple Choice Guestions (Type-I)

1. (iv)

2. (i)

3. (iii)

4. (iv)

5. (i)

6. (i)

7. (i)

8. (iii)

9. (ii)

10. (i)

11. (i)

12. (i)

13. (ii)

14. (i)

15. (iii)

16. (i)

17. (iv)

18. (ii)

19. (i)

20. (iii)

21. (iv)

II. Multiple Choice Questions (Type-II)

22. (ii), (iv)

23. (i), (iii)

24. (i), (ii)

25. (ii), (iii)

26. (i), (iii)

27. (i), (ii)

28. (i), (ii)

III. Short Answer Type

31. (i) $O_2^{2-}+2 H_2 O \longrightarrow 2 OH^{-}+H_2 O_2$

(ii) $2 O_2^{-}+2 H_2 O \longrightarrow 2 OH^{-}+H_2 O_2+O_2$

IV. Matching Type

41. (i) $\to$ (c), $\quad$ (ii) $\to$ (b), $\quad$ (iii) $\to$ (d), $\quad$ (iv) $\to$ (a), (e)

42. (i) $\to$ (c), $\quad$ (ii) $\to$ (d), $\quad$ (iii) $\to$ (b), $\quad$ (iv) $\to$ (a)

43. (i) $\to$ (f), $\quad$ (ii) $\to$ (d), $\quad$ (iii) $\to$ (b), $\quad$ (iv) $\to$ (c) $\quad$ (v) $\to$ (e), $\quad$ (vi) $\to$ (a)

V. Assertion and Reason Type

44. (i)

45. (i)

V. Long Answer Type

50. Compound: $A: CaO ; B: Ca(OH)_2 ; C: CaCO_3 ; D: Ca(HCO_3)_2$

$Ca(HCO_3)_2$ is soluble in water. Hence, milkiness of solution disappears on passing excess carbon dioxide into the solution of compound B.

51. $8 LiH+Al_2 Cl_6 \longrightarrow 2 Li Al H_4+6 LiCl$

$LiAl H_4+2 BeCl_2 \longrightarrow 2 BeH_2+LiCl+AlCl_3$

52. The element is beryllium

53. The element is sodium.

Unnit 11

The p-Block Elements

I. Multiple Choice Questions (Type-I)

1. The element which exists in liquid state for a wide range of temperature and can be used for measuring high temperature is

(i) $B$

(ii) $Al$

(iii) Ga

(iv) In

2. Which of the following is a Lewis acid?

(i) $AlCl_3$

(ii) $MgCl_2$

(iii) $CaCl_2$

(iv) $BaCl_2$

3. The geometry of a complex species can be understood from the knowledge of type of hybridisation of orbitals of central atom. The hybridisation of orbitals of central atom in $[Be(OH)_4]^{-}$and the geometry of the complex are respectively

(i) $s p^{3}$, tetrahedral

(ii) $s p^{3}$, square planar

(iii) $s p^{3} d^{2}$, octahedral

(iv) $d s p^{2}$, square planar

4. Which of the following oxides is acidic in nature?

(i) $B_2 O_3$

(ii) $Al_2 O_3$

(iii) $Ga_2 O_3$

(iv) $In_2 O_3$

5. The exhibition of highest co-ordination number depends on the availability of vacant orbitals in the central atom. Which of the following elements is not likely to act as central atom in $MF_6^{3-}$ ?

(i) $B$

(ii) $Al$

(iii) $Ga$

(iv) In

6. Boric acid is an acid because its molecule

(i) contains replaceable $H^{+}$ion

(ii) gives up a proton

(iii) accepts $OH^{-}$from water releasing proton

(iv) combines with proton from water molecule

7. Catenation i.e., linking of similar atoms depends on size and electronic configuration of atoms. The tendency of catenation in Group 14 elements follows the order:

(i) $C>Si>Ge>Sn$

(ii) $C»Si>Ge \approx Sn$

(iii) $Si>C>Sn>Ge$

(iv) $Ge>Sn>Si>C$

8. Silicon has a strong tendency to form polymers like silicones. The chain length of silicone polymer can be controlled by adding

(i) $MeSiCl_3$

(ii) $Me_2 SiCl_2$

(iii) $Me_3 SiCl$

(iv) $Me_4 Si$

9. Ionisation enthalpy $(\Delta_i H_1 kJ mol^{-1})$ for the elements of Group 13 follows the order.

(i) $B>Al>Ga>$ In $>Tl$

(ii) $B<Al<Ga<$ In $<Tl$

(iii) $B < Al > Ga < In > Tl$

(iv) $ B > Al < Ga >$ In $<Tl$

10. In the structure of diborane

(i) All hydrogen atoms lie in one plane and boron atoms lie in a plane perpendicular to this plane.

(ii) 2 boron atoms and 4 terminal hydrogen atoms lie in the same plane and 2 bridging hydrogen atoms lie in the perpendicular plane.

(iii) 4 bridging hydrogen atoms and boron atoms lie in one plane and two terminal hydrogen atoms lie in a plane perpendicular to this plane.

(iv) All the atoms are in the same plane.

11. A compound $X$, of boron reacts with $NH_3$ on heating to give another compound $Y$ which is called inorganic benzene. The compound $X$ can be prepared by treating $BF_3$ with Lithium aluminium hydride. The compounds $X$ and $Y$ are represented by the formulas.

(i) $B_2 H_6, B_3 N_3 H_6$

(ii) $B_2 O_3, B_3 N_3 H_6$

(iii) $BF_3, B_3 N_3 H_6$

(iv) $B_3 N_3 H_6, B_2 H_6$

12. Quartz is extensively used as a piezoelectric material, it contains

(i) $Pb$

(ii) $Si$

(iii) $Ti$

(iv) Sn

13. The most commonly used reducing agent is

(i) $AlCl_3$

(ii) $PbCl_2$

(iii) $SnCl_4$

(iv) $SnCl_2$

14. Dry ice is

(i) Solid $NH_3$

(ii) Solid $SO_2$

(iii) Solid $CO_2$

(iv) Solid $N_2$

15. Cement, the important building material is a mixture of oxides of several elements. Besides calcium, iron and sulphur, oxides of elements of which of the group (s) are present in the mixture?

(i) group 2

(ii) groups 2, 13 and 14

(iii) groups 2 and 13

(iv) groups 2 and 14

II. Multiple Choice Questions (Type-II)

In the following questions two or more options may be correct.

16. The reason for small radius of Ga compared to $Al$ is ———.

(i) poor screening effect of $d$ and $f$ orbitals

(ii) increase in nuclear charge

(iii) presence of higher orbitals

(iv) higher atomic number

17. The linear shape of $CO_2$ is due to ———.

(i) $s p^{3}$ hybridisation of carbon

(ii) $s p$ hybridisation of carbon

(iii) $\quad p \pi-p \pi$ bonding between carbon and oxygen

(iv) $s p^{2}$ hybridisation of carbon

18. $Me_3 SiCl$ is used during polymerisation of organo silicones because

(i) the chain length of organo silicone polymers can be controlled by adding $Me_3 SiCl$

(ii) $Me_3 SiCl$ blocks the end terminal of silicone polymer

(iii) $Me_3 SiCl$ improves the quality and yield of the polymer

(iv) $Me_3 SiCl$ acts as a catalyst during polymerisation

19. Which of the following statements are correct?

(i) Fullerenes have dangling bonds

(ii) Fullerenes are cage-like molecules

(iii) Graphite is thermodynamically most stable allotrope of carbon

(iv) Graphite is slippery and hard and therefore used as a dry lubricant in machines

20. Which of the following statements are correct. Answer on the basis of Fig.11.1.

(i) The two birdged hydrogen atoms and the two boron atoms lie in one plane;

(ii) Out of six $B-H$ bonds two bonds can be described in terms of 3 centre 2 -electron bonds.

(iii) Out of six B-H bonds four B-H bonds can be described in terms of 3 centre 2 electron bonds;

Fig. 11.1

(iv) The four terminal B-H bonds are two centre-two electron regular bonds.

21. Identify the correct resonance structures of carbon dioxide from the ones given below :

(i) $O-C \equiv O$

(ii) $O=C=O$

(iii) ${ }^{-} O \equiv C-O^{+}$

(iv) ${ }^{-} O-C \equiv O^{+}$

III. Short Answer Type

22. Draw the structures of $BCl_3 \cdot NH_3$ and $AlCl_3$ (dimer).

23. Explain the nature of boric acid as a Lewis acid in water.

24. Draw the structure of boric acid showing hydrogen bonding. Which species is present in water? What is the hybridisation of boron in this species?

25. Explain why the following compounds behave as Lewis acids?

(i) $BCl_3$

(ii) $AlCl_3$

26. Give reasons for the following:

(i) $CCl_4$ is immiscible in water, whereas $SiCl_4$ is easily hydrolysed.

(ii) Carbon has a strong tendency for catenation compared to silicon.

27. Explain the following:

(i) $CO_2$ is a gas whereas $SiO_2$ is a solid.

(ii) Silicon forms $SiF_6 _6^{2-}$ ion whereas corresponding fluoro compound of carbon is not known.

28. The +1 oxidation state in group 13 and +2 oxidation state in group 14 becomes more and more stable with increasing atomic number. Explain.

29. Carbon and silicon both belong to the group 14, but inspite of the stoichiometric similarity, the dioxides, (i.e., carbon dioxide and silicon dioxide), differ in their structures. Comment.

30. If a trivalent atom replaces a few silicon atoms in three dimensional network of silicon dioxide, what would be the type of charge on overall structure?

31. When $BCl_3$ is treated with water, it hydrolyses and forms $[B[OH]_4]^{-}$only whereas $AlCl_3$ in acidified aqueous solution forms $[Al(H_2 O)_6]^{3+}$ ion. Explain what is the hybridisation of boron and aluminium in these species?

32. Aluminium dissolves in mineral acids and aqueous alkalies and thus shows amphoteric character. A piece of aluminium foil is treated with dilute hydrochloric acid or dilute sodium hydroxide solution in a test tube and on bringing a burning matchstick near the mouth of the test tube, a pop sound indicates the evolution of hydrogen gas. The same activity when performed with concentrated nitric acid, reaction doesn’t proceed. Explain the reason.

33. Explain the following :

(i) Gallium has higher ionisation enthalpy than aluminium.

(ii) Boron does not exist as $B^{3+}$ ion.

(iii) Aluminium forms $[AlF_6]^{3-}$ ion but boron does not form $[BF_6]^{3-}$ ion.

(iv) $PbX_2$ is more stable than $PbX_4$.

(v) $Pb^{4+}$ acts as an oxidising agent but $Sn^{2+}$ acts as a reducing agent.

(vi) Electron gain enthalpy of chlorine is more negative as compared to fluorine.

(vii) $Tl(NO_3)_3$ acts as an oxidising agent. (viii) Carbon shows catenation property but lead does not.

(ix) $BF_3$ does not hydrolyse.

(x) Why does the element silicon, not form a graphite like structure whereas carbon does.

34. Identify the compounds $A, X$ and $Z$ in the following reactions :

(i)

$ \begin{gathered} A+2 HCl+5 H_2 O \longrightarrow 2 NaCl+X \\ X \xrightarrow[370 K]{\Delta} HBO_2 \xrightarrow[>370 K]{ } Z \end{gathered} $

35. Complete the following chemical equations :

$Z+3 LiAlH_4 \longrightarrow X+3 LiF+3 AlF_3$

$X+6 H_2 O \longrightarrow Y+6 H_2$

$3 X+3 O_2 \xrightarrow{\Delta} B_2 O_3+3 H_2 O$

IV. Matching Type

In the following questions more than one correlation is possible between options of Column I and Column II. Make as many correlations as you can.

36. Match the species given in Column I with the properties mentioned in Column II.

37. Match the species given in Column I with properties given in Column II.

38. Match the species given in Column I with the hybridisation given in Column II.

V. Assertion and Reason Type

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

39. Assertion (A): If aluminium atoms replace a few silicon atoms in three dimensional network of silicon dioxide, the overall structure acquires a negative charge.

Reason (R) : Aluminium is trivalent while silicon is tetravalent.

(i) Both $A$ and $R$ are correct and $R$ is the correct explanation of $A$.

(ii) Both $A$ and $R$ are correct but $R$ is not the correct explanation of $A$.

(iii) Both $A$ and $R$ are not correct

(iv) $A$ is not correct but $R$ is correct.

40. Assertion (A): Silicons are water repelling in nature.

Reason (R) : Silicons are organosilicon polymers, which have $(-R_2 SiO-)$ as repeating unit.

(i) $A$ and $R$ both are correct and $R$ is the correct explanation of $A$.

(ii) Both $A$ and $R$ are correct but $R$ is not the correct explanation of $A$.

(iii) $A$ and $R$ both are not true.

(iv) $A$ is not true but $R$ is true.

VI. Long Answer Type

41. Describe the general trends in the following properties of the elements in Groups 13 and 14.

(i) Atomic size $\quad$ (ii) Ionisation enthalpy

(iii) Metallic character $\quad$ (iv) Oxidation states

(v) Nature of halides

42. Account for the following observations:

(i) $AlCl_3$ is a Lewis acid

(ii) Though fluorine is more electronegative than chlorine yet $BF_3$ is a weaker Lewis acid than $BCl_3$

(iii) $PbO_2$ is a stronger oxidising agent than $SnO_2$

(iv) The +1 oxidation state of thallium is more stable than its +3 state.

43. When aqueous solution of borax is acidified with hydrochloric acid, a white crystalline solid is formed which is soapy to touch. Is this solid acidic or basic in nature? Explain.

44. Three pairs of compounds are given below. Identify that compound in each of the pairs which has group 13 element in more stable oxidation state. Give reason for your choice. State the nature of bonding also.

(i) $TlCl_3, TlCl$

(ii) $AlCl_3, AlCl$

(iii) $InCl_3, InCl$

45. $BCl_3$ exists as monomer whereas $AlCl_3$ is dimerised through halogen bridging. Give reason. Explain the structure of the dimer of $AlCl_3$ also.

46. Boron fluoride exists as $BF_3$ but boron hydride doesn’t exist as $BH_3$. Give reason. In which form does it exist? Explain its structure.

47. (i) What are silicones? State the uses of silicones.

(ii) What are boranes? Give chemical equation for the preparation of diborane.

48. A compound (A) of boron reacts with $NMe_3$ to give an adduct (B) which on hydrolysis gives a compound (C) and hydrogen gas. Compound (C) is an acid. Identify the compounds A, B and C. Give the reactions involved.

49. A nonmetallic element of group 13, used in making bullet proof vests is extremely hard solid of black colour. It can exist in many allotropic forms and has unusually high melting point. Its trifluoride acts as Lewis acid towards ammonia. The element exihibits maximum covalency of four. Identify the element and write the reaction of its trifluoride with ammonia. Explain why does the trifluoride act as a Lewis acid.

50. A tetravalent element forms monoxide and dioxide with oxygen. When air is passed over heated element (1273 K), producer gas is obtained. Monoxide of the element is a powerful reducing agent and reduces ferric oxide to iron. Identify the element and write formulas of its monoxide and dioxide. Write chemical equations for the formation of producer gas and reduction of ferric oxide with the monoxide.

ANSWERS

I. Multiple Choice Questions (Type-I)

1. (iii)

2. (i)

3. (i)

4. (i)

5. (i)

6. (iii)

7. (ii)

8. (iii)

9. (iv)

10. (ii)

11. (i)

12. (ii)

13. (iv)

14. (iii)

15. (ii)

II. Multiple Choice Questions (Type-II)

16. (i), (ii)

17. (ii), (iii)

18. (i), (ii)

19. (ii), (iii)

20. (i), (ii), (iv)

21. (ii), (iv)

III. Short Answer Type

23. Boric acid acts as Lewis acid in water by accepting a pair of electrons from a hydroxyl ion :

$B(OH)_3+2 HOH \longrightarrow[B(OH)_4]^{-}+H_3 O^{+}$

24. Species present in water is $[B(OH)_4]^{-}$. Boron is $s p^{3}$ hybridised.

25. $BCl_3$ and $AlCl_3$ being electron deficient due to incomplete octet of central metal atom behave as Lewis acids.

26. $CCl_4$ is a covalent compound. Hence, insoluble in water whereas $SiCl_4$ is soluble because $Si$ atom in $SiCl_4$ can accomodate the lone pair of electrons obtained from oxygen atom of water molecule in $d$-orbitals.

27. (i) Very high $Si-O$ bond enthalpy and ionic character of $Si-O$ bond.

(ii) Vacant $3 d$ orbitals are available on $Si$ atom to accomodate electrons and expand coordination number upto 6.

29. [Hint : In $CO_2$, carbon is $s p$ hybridised and it is a linear molecule. In $SiO_2$, $Si$ is tetrahedrally bonded to four oxygen atoms.]

30. Negative

32. [Hint : Conc. $HNO_3$ renders aluminium passive by forming a protective oxide layer on the surface.]

34. A : $Na_2 B_4 O_7$ (Borax)

$X: H_3 BO_3$

$Z \quad: \quad B_2 O_3$

35. | $A$ | $:$ | $BF_3$ | | :— | :— | :— | | $X$ | $:$ | $B_2 H_6$ | | $Y$ | $;$ | $H_3 BO_3$ |

IV. Matching Type

36. (i) $\to$ (e) $\quad$ (ii) $\to$ (c) $\quad$ (iii) $\to$ (d) $\quad$ (iv) $\to$ (a), (b)

37. (i) $\to$ (c) $\quad$ (ii) $\to$ (d) $\quad$ (iii) $\to$ (a) $\quad$ (iv) $\to$ (e) $\quad$ (v) $\to$ (b)

38. (i) $\to$ (b), $\quad$ (ii) $\to$ (c), $\quad$ (iii) $\to$ (b), $\quad$ (iv) $\to$ (a), $\quad$(v) $\to$ (b), $\quad$ (vi)$\to$ (c)

V. Assertion and Reason Type

39. (i)

40. (ii)

V. Long Answer Type

45. [Hint : Absence of $d$-orbitals in boron.]

46. $A=B_2 H_6, \quad B=BH_3 \cdot NMe_3, \quad C=B(OH)_3$ i.e. $H_3 BO_3$.