Boron family

Question 1

Protective influence of fluoride ions against tooth decay:

Answer 1

Ca5(PO4)3OH(s) + F–(aq) → Ca5(PO4)3F(s) + OH–(aq) Ca5(PO4)3OH(t) + NaF → Ca5(PO4)3F + NaOH

Question 2

Production of boron:

Answer 2

B2O3(s) + 3 Mg(s) →2 B(s) + 3 MgO(s)

Question 3

Production of very pure boron:

Answer 3

2 BBr3(g) + 3 H2(g) → 2 B(s) + 6 HBr(g)

Question 4

Production of aluminum by electrolysis:

Answer 4

On cathode Al3+(melt) + 3e– → Al(l)
On anode 2 O2–(melt) + C(t, gr) → CO2(g) + 4e– In summary:
4 Al3+(melt) + 6 O2–(melt) + 3 C(t, gr) → 4 Al(l) + 3
CO2(g)
2Al2O3 +3 C ⎯⎯⎯⎯⎯⎯⎯⎯ 4 Al + 3 CO2

Question 5

Reaction of aluminum with acids:

Answer 5

2 Al(s) + 6 H+(aq) → 2 Al3+(aq) + 3 H2(g)
2 Al + 3H2SO4 → Al2(SO4)3 + 3 H2

Question 6

Reaction of aluminum with hot alkali:

Answer 6

2 Al(s) + 2 OH–(aq) + 6 H2O(l) → 2 Al(OH)4–(aq) + 3
H2(g)
2 Al + 2 NaOH + 6 H2O → 2 Na[Al(OH)4] + 3 H2

Question 7

Acidic nature of B(OH)3:

Answer 7

(OH)3B + :OH2 → (OH)3B–OH2
B(OH)3OH2(aq) + H2O(l) ⇌ H3O+(aq) + B(OH)4−(aq)

Question 8

Reaction of γ-Al2O3 with acids and alkali:

Answer 8

Al2O3(s) + 2 OH−(aq) + 3 H2O(l) → 2 Al(OH)4−(aq)
Al2O3 + 6 HCl → 2 AlCl3
Al2O3(s) + 6 H3O+(aq) + 3 H2O(l) → 2 Al(H2O)63+(aq)
Al2O3 + 2 NaOH + 3 H2O → 2 Na[Al(OH)4]

Question 9

Acidic nature of hydrated Al3+-ions:

Answer 9

Al(H2O)63+(aq) + H2O(l) ⇌ H3O+(aq) + Al(OH)(H2O)52+(aq)

Question 10

Production of Al2(SO4)3:

Answer 10

Al2O3(s) + 3 H2SO4(aq) → Al2(SO4)3(aq) + 3 H2O(l)

Question 11

Use of sodium aluminate and aluminum sulfate for water purification:

Answer 11

Al3+(aq) + 3 Al(OH)4−(aq) → 4 Al(OH)3(s)
Al2(SO4)3 + 6 Na[Al(OH)4] → 8 Al(OH)3 + 3 Na2SO4

Question 12

Production of boron nitride:

Answer 12

2 B(s) + 2 NH3(g) →2 BN(s) + 3 H2(g)

Question 13

Production of boron trifluoride:

Answer 13

B2O3(s) + 3 CaF2(s) + 3 H2SO4(l) →2 BF3(g) + 3 CaSO4(s) + 3 H2O(l)

Question 14

Production of boron trichloride:

Answer 14

B2O3(s) + 3 C(s) + 3 Cl2(g) → 2 BCl3(g) + 3 CO(g)

Question 15

Production of aluminum chloride:

Answer 15

2 Al(s) + 3 Cl2(g) → 2 AlCl3(s)
Al2O3(s) + 3 C(s) + 3 Cl2(g) → 2 AlCl3(s) + 3 CO(g)

Question 16

Production of sodium borohydride:

Answer 16

4 NaH + BCl3 → NaBH4 + 3 NaCl

Question 17

Production of diborane:

Answer 17

4 BF3 + 3 BH4– → 3 BF4– + 2 B2H6
4 BF3 + 3 NaBH4 → 3 NaBF4 + 2 B2H6

Question 18

Reaction of diborane with water:

Answer 18

B2H6(g) + 6 H2O(l) → 2 B(OH)3 + 6 H2(g)

Question 19

Decomposition of diborane:

Answer 19

B2H6(g) →2 B(s) + 3 H2(g)