Period 3

Question 1

pH of period 3 oxides

Answer 1

13 9 7 7 3 2 1

Question 2

pH of period 3 chlorides

Answer 2

7 6.5 3 2 2

Question 3

Reaction of Sodium oxide with water

Answer 3

Na2O + H2O -> 2NaOH

Question 4

Reaction of magnesium oxide with water

Answer 4

MgO + H2O -> Mg(OH)2
Reversible arrow

Question 5

Why does Na2O and MgO dissolve

Answer 5

Hydration energy evolved from ion-dipole interactions between Na+ and water and O2- and water are
able to overcome the strong ionic bonds between Na+ and O2-

Question 6

Aluminium and silicon oxide with water

Answer 6

Insoluble since
Al: hydration energy evolved from ion dipole interactions…not strong enough to overcome strong ionic bonds between
Si: weak id-id forces with water molecules not strong enough to break strong covalent bonds between Si and O atoms

Question 7

Phosphorous oxide and water

Answer 7

P4O6 + H2O -> 4H3PO3
P4O10 + H2O -> 4H3PO4

Question 8

Sulfur oxides with water

Answer 8

SO2 + H2O -> H2SO3
SO3 + H2O -> H2SO4 (strongly acidic)

Question 9

Sodium oxides and hydroxides with acids, bases

Answer 9

Na2O + 2HCl -> 2NaCl + H2O
NaOH + HCl -> NaCl + H2O

Question 10

Magnesium oxides and hydroxides with acids and bases

Answer 10

MgO + 2HCl -> Mg(Cl)2 + H2O
Mg(OH)2 + 2HCl -> Mg(Cl)2 + 2H2O

Question 11

Aluminium oxides and hydroxides with acids and base

Answer 11

Al2O3 + 6HCl -> 2Al(Cl)3 + 3H2O
Al2O3 + 2NaOH + 3H2O -> 2NaAl(OH)4

Al(OH)3 + 3HCl -> Al(Cl)3 + 3H2O
Al(OH)3 + OH- -> Al(OH)4-

Question 12

Silicon oxides and hydroxides with acids and bases

Answer 12

SiO2 + 2NaOH -> NaSiO3 + H2O
Silicon hydroxides do not react

Question 13

Phosphorus oxides and hydroxides with bases

Answer 13

P4O6 + 8NaOH -> 4Na2HPO3 + 2H2O
P4O10 + 12NaOH -> 4Na3PO4 + 6H2O

H3PO3 + NaOH -> NaHPO3 + H2O
H3PO4 + NaOH -> NaPO4 + H2O

Question 14

Sulfur oxides and hydroxides with acids and bases

Answer 14

SO2 + NaOH -> Na2SO3 + H2O
SO3 + 2NaOH -> Na2SO4 + H2O

H2SO3 + 2NaOH -> Na2SO3 + 2H2O
H2SO4 + 2NaOH -> Na2SO4 + 2H2O

Question 15

Sodium chloride and water

Answer 15

NaCl + aq -> Na+ + Cl-
Na+ has high charge density so it doesn’t undergo hydrolysis

Question 16

Magnesium chloride and water

Answer 16

MgCl2 + 6H2O -> [Mg(H2O)6]2+ + Cl2
[Mg(H2O)6]2+ + H2O -> [Mg(H2O)5(OH)] + H3O+

Question 17

Aluminium chloride and water
(1) Readily dissolves to form hydrated Al3+ ion which undergoes hydrolysis in large amts of water
(2) White solid and white fumes of HCl formed with limited amt of water

Answer 17

(1)
AlCl3 + 6H2O -> [Al(H2O)6]3+ + 3Cl-
[Al(H2O)6]3+ + H2O -> [Al(H2O)5(OH)] + H3O+

(2)
AlCl3 + 3H2O -> Al(OH)3 + HCl
2AlCl3 + 3H2O -> Al2O3 + 6HCl

Al3+ has high charge density, hence able to polarise the water molecules, breaking the O-H bond to form H3O+ ion which is acidic

Question 18

Silicon chloride and water

Answer 18

SiCl4 + 2H2O -> SiO2 + 4HCl

When sicl4 dissolves, slightly positive Si atom attract the slightly negative O atom from water -> break OH bond and release H+

Question 19

Phosphorous chloride and water

Answer 19

PCl3 + 3H2O -> H3PO3 + 3HCl
PCl5 + 4H2O -> H3PO4 + 5HCl

Limited amount of water or cold:
PCl5 + H2O -> POCl3 + 2HCl
POCl3 + 3H2O -> H3PO4 + 3HCl