Period 3 and their oxides

Question 1

State the observations with sodium + water and write the equation

Answer 1

• fizzing, melts to form a ball and floats
• 2Na +2H2O → 2NaOH +H2

Question 2

State the observations with Magnesium + cold water and write the equation

Answer 2

• very slow, small bubbles of gas after a few days
• forms a weak alkaline solution
• Mg + 2H2O → Mg(OH)2 +H2

Question 3

Explain why sodium is more reactive than magnesium

Answer 3

• ∵ it takes less energy to lose 1 electron than to lose 2
• ∴ more energy (usually heat) is needed for magnesium to react

Question 4

State the observations with Magnesium + steam and write the equation

Answer 4

• bright light
• Mg + H2O → MgO + H2

Question 5

Why is magnesium hydroxide not produced in Magnesium + steam

Answer 5

because Mg(OH)2 decomposes at high temperature

Question 6

State the observations with chlorine + cold water and write the equation?

Answer 6

• forms a pale green solution (pale green is due to the presence of chlorine)
• equilibrium is established
• Cl2 + H2O = HCl + HCLO

Question 7

State the observations with chlorine + cold water in the presence of SUNLIGHT and write the equation.

Answer 7

• a colourless gas is formed and the pale green colour fades

Cl2 + 2H2O → 4HCL +O2

Question 8

Describe the trend across period 3 in the reaction with oxygen

Answer 8

• metal oxides are formed
• all the metals are oxidised to their greatest oxidation state which is the same as their group number
• Na and Mg are both ionic lattices
• Aluminium is ionic but has some covalent character
• Si is macro-molecular and P, S are all molecular

Question 9

Why is there a degree of covalent bonding with aluminium oxide?

Answer 9

aluminium ion is very small and positively charged and can distort the oxygen’s electron cloud.

Question 10

State the observations with Sodium + oxygen and write the equation

Answer 10

• 4Na + O2 → 2Na2O
• yellow flame and yellow solid

Question 11

State the observations with Magnesium + oxygen and write the equation

Answer 11

• 2Mg + O2 → 2MgO
• bright white light and crumbly whitle solid formed

Question 12

State the observations with Aluminium + oxygen and write the equation

Answer 12

• Bright white light and white flaky powder
• 4Al + 3O2 → 2Al2O3

Question 13

State the observations with Silicon + oxygen and write the equation

Answer 13

• Si + O2 → SiO2
• reaction gives off light

Question 14

State the observations with Phosphorus + oxygen and write the equation

Answer 14

• bright white light and white solid
• P4 + 5O2 (g) → P4O10

Question 15

State the observations with Sulfur + oxygen and write the equation

Answer 15

• blue flame and smelly gas
• S+ O2 → SO2

Question 16

Describe the trend in melting point of the period 3 oxides and describe how their bonding and structure affects this

Answer 16

• Na2 O, MgO and Al2O3 are metal oxides. They have high melting points because they form giant ionic lattices = strong forces of attraction between oppositely charged ions - a lot of heat energy to break the bonds
• MgO has a higher melting point than Na2O because Mg forms 2+ ions, so bonds more strongly than the 1+ Na ions in Na2O.
• Al2O3 has a lower melting point than you might expect because the highly charged Al3+ ions distort the oxygen’s electron cloud making the bonds partially covalent.
• SiO, has a higher melting point than the other non-metal oxides because it has a giant macromolecular structure = the strong covalent bonds between atoms need to be broken
• P4O10 and SO2 have relatively low melting points because they form simple molecular structures. The molecules are bound by weak intermolecular forces (dipole-dipole and van der Waals), which take little energy to break.

Question 17

How does sodium oxide and magnesium oxide react with water? Write the equations

Answer 17

• both of these oxides are basic as the oxide ions react with water and accept a proton to from hydroxide ions (O^{2 -} +H₂O -> 2OH^-)
• Sodium reacts to give a strongly alkaline solution
• Magnesium reacts to give a somewhat alkaline solution

Question 18

What are the insoluble oxides formed in period 3. Why are they insoluble?

Answer 18

aluminium oxide = very high lattice enthalpy

silicon dioxide = giant covalent so strong covalent bonds would have to be broken

Question 19

What are the oxides in period 3 that act as acids in the reaction with water? Explain the chemistry behind this and write the equations

Answer 19

phosphorus pentoxide, sulfur dioxide and sulfur trioxide

H2O molecules attack d+ P/S atoms, leading to the release of H+ from the water molecules

Question 20

What are the conditions for silicon dioxide + alkali? Write the equation

Answer 20

hot concentrated NaOH

Question 21

Write the equations for how basic oxides neutralise acids

Answer 21

Question 22

Write the equation for how P4O neutralise base

Answer 22

Question 23

Write the equations for how S^4+ and S^6+ neutralise bases

Answer 23

Question 24

Explain why sodium oxide forms an alkaline solution when it reacts with water.

Answer 24

• Sodium oxide contains $O^{2–}$ ions
• These $O^{2–}$ ions react with water forming OH– ions

Question 25

Explain why sodium oxide forms a solution with a higher pH than the solution formed from magnesium oxide

Answer 25

**Magnesium oxide is less soluble than sodium oxide**, - the reaction of magnesium oxide with water will only partially dissociate into its ions, a less alkaline solution than with sodium oxide is formed.

Question 26

What is the aluminium oxide reaction with acid and bases?

Answer 26

Question 27

Suggest why silicon dioxide is described as an acidic oxide even though it is insoluble in water.

Answer 27

SiO2 reacts with bases / NaOH / CaO / CaCO3