4. Properties of Period 3 elements and their oxides Flashcards
Which metal elements in period 3 react with cold water?
Sodium and magnesium
Which elements in period 3 react with steam under certain conditions?
Aluminium and silicon
Which elements in period 3 do not react with water?
Phosphorous, sulphur and argon
Which elements in period 3 react with cold water?
Sodium, magnesium and chlorine
What happens when sodium is added to water?
- reacts vigorously to form alkaline solution
- floats on surface, fizzes and becomes molten
- may also catch fire and burn with a yellow flame
Symbol equation for reaction of sodium with cold water?
2Na + 2H₂O → 2NaOH + H₂
What happens when magnesium is added to cold water?
- reacts very slowly
* forms a less alkaline solution than sodium
Symbol equation for reaction of magnesium with cold water?
Mg + 2H₂O → Mg(OH)₂ + H₂
What happens when magnesium is added to steam?
- reacts vigorously
* produces a different product to Mg + water
Symbol equation for reaction of magnesium with steam?
Mg + H₂O → MgO + H₂
What types of reaction are sodium and magnesium with water?
Redox
In the redox reactions of Mg and Na with H₂O, which is oxidised and which is reduced?
Metal is oxidised, water is reduced
Why does sodium react more vigorously than magnesium with water?
- Na has 1+ ions whereas Mg has 2+
* stronger electrostatic forces of attraction between Mg ions and delocalised electrons
What type of reaction is that of chlorine with water?
Disproportionation
Symbol equation for reaction of chlorine with water?
Cl₂ + H₂O ⇌ HClO + HCl
What happens when chlorine is added to H₂O?
- disproportionation reaction
* gives acidic solution
How do all period 3 elements react with oxygen?
Redox reaction - except chlorine and argon
Which P3 elements do not react with oxygen in a redox reaction?
Chlorine and argon
Which oxides are formed when P3 elements react with oxygen?
- Na₂O
- MgO
- Al₂O₃
- SiO₂
- P₄O₁₀
- SO₂
- SO₃
Observations for when Na reacts with oxygen?
- yellow flame
- produce white solid
- reacts vigorously
Observations for when Mg reacts with oxygen?
- bright white flame
* produce white solid
Observations for when Al reacts with oxygen?
- not as vigorous as Mg or Na
- bright white flame
- white solid produced
Observations for when Si reacts with oxygen?
- bright white flame
* forms white solid - silicon dioxide
Observations for when P₄ reacts with oxygen?
- spontaneously ignites in air
- white flame
- white smoke produced - phosphorous oxide
In limited oxygen, what can P₄ produce?
P₄O₆ (as oppose to P₄O₁₀)
Observations for when S₈ reacts with oxygen?
- blue flame
- produce colourless gas - sulphur dioxide
- sometimes small amounts of sulphur trioxide produced
Equation for Na with oxygen?
4Na + O₂ → 2Na₂O
Equation for Mg with oxygen?
2Mg + O₂ → 2MgO
Equation for Al with oxygen?
4Al + 3O₂ → 2Al₂O₃
Equation for Si with oxygen?
Si + O₂ → SiO₂
Equation for P₄ with oxygen?
4P + 5O₂ → P₄O₁₀
Equation for S₈ with oxygen?
S + O₂ → SO₂
S₈ + 8O₂ → 8SO₂
What is the structure of Na₂O?
Ionic
What is the structure of MgO?
Ionic
What is the structure of Al₂O₃?
Ionic with covalent character
What is the structure of SiO₂?
Giant covalent
What is the structure of P₄O₁₀?
Molecular covalent
What is the structure of SO₃?
Molecular covalent
What is the structure of SO₂?
Molecular covalent
Which P3 oxides have a high melting point?
Na₂O, MgO and Al₂O₃
Why do MgO and Al₂O₃ have higher melting points than Na₂O?
- Na forms 1+ ion, Mg forms 2+, Al forms 3+
* so stronger ionic bonds in Mg and Al
Why is the melting point of Al₂O₃ lower than that of MgO?
Al₂O₃ is ionic with covalent character, so molecules are further from each other → weaker electrostatic forces
Why does Al₂O₃ have covalent character?
Al 3+ so highly charged and small - so can attract electrons towards itself
Why does SiO₂ have a high melting point?
Strong covalent bonds only which take a lot of energy to overcome
Which P3 oxides have a low melting point?
P₄O₁₀, SO₂ and SO₃
Why do the P3 molecular oxides have a much lower melting point?
They have weak IMFs which don’t take a lot of energy to overcome
Why is there a decrease in melting point in the P3 molecular oxides?
They decrease in size so fewer electrons and temporary dipole is weaker - so weaker VDW forces
Which three groups can the P3 oxides be classified as?
- Ionic oxides
- Giant covalent oxide
- Molecular covalent oxides
What do ionic oxides react with water to produce?
Hydroxide ions
What ion do ionic oxides contain?
O²⁻
Are ionic oxides acidic or basic?
basic
Is Na₂O soluble in water?
Very soluble - many OH- ions formed
What pH solution is formed when sodium oxide is added to water?
Alkaline - 13 to 14
Is MgO soluble in water?
Slightly soluble - few O²⁻ ions in solution and so only few OH- ions are forming
What pH solution is formed when magnesium oxide is added to water?
Weakly alkaline - 10
Is Al₂O₃ soluble in water?
No - no OH- ions formed and pH of water is unaffected
What pH solution is formed when aluminium oxide is added to water?
Remains at 7
Why can Al₂O₃ show some acidic characteristics?
- electronegativity difference between Al and O is less than Na and O - so significant covalent character
- this allows it to show acidic characteristics as well as being a metal oxide and therefore showing basic characteristics
Is SiO₂ is soluble in water?
No - macromolecule so very stable
also small difference in electronegativity between Si and O so minimal attraction for the water molecules
Why are covalent oxides acidic?
- don’t contain ions, but have strongly +ve dipole on the atom that isn’t oxygen
- attracts lone pair on water molecules - releasing H+
How does P₄O₁₀ react with water?
- violently
* forms phosphoric acid - which ionises in the solution
Equation for P₄O₁₀, with water?
P₄O₁₀, + 6H₂O → 4H₃PO₄
↓
H₂PO₄ → H⁺ + H₂PO₄⁻
How do SO₂ and SO₃ react with water?
- give acidic solutions
* SO₃ reacts more vigorously - more H+ ions produced - lower pH
pH after SO₂ has reacted with water?
2-3
pH after SO₃ has reacted with water?
1-3
Equation for SO₂ with water?
SO₂ + H₂O → H+ + HSO₃- (H₂SO₃, sulphurous acid)
Equation for SO₃ with water?
SO₃ + H₂O → H+ + HSO₄- (strongly acidic solution of sulphuric acid)
What does SO₃ with water produce?
Strongly acidic solution of sulphuric acid
What happens to the oxides across period 3, in terms of acids and bases?
Across the period they go from basic to acidic
What do ionic oxides react with compared to covalent oxides?
- ionic with acids
- covalent with bases
(neutralisation)
What do Na₂O and MgO react with acids to give?
Salt and water
Equation for Na₂O with HCl?
Na₂O + 2HCl → 2NaCl + H₂O
Equation for MgO with HCl?
MgO + 2HCl → MgCl₂ + H₂O
Equation for MgO with sulfuric acid?
MgO + H₂SO₄ → MgSO₄ + H₂O
Equation for Na₂O with nitric acid?
Na₂O + 2HNO₃ → 2NaNO₃ + H₂O
What does it mean that Al₂O₃ is an amphoteric oxide?
It reacts with both acids and alkalis
Equation for Al₂O₃ with HCl?
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
Equation for Al₂O₃ with sulphuric acid?
Al₂O₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂O
Equation for Al₂O₃ with nitric acid?
Al₂O₃ + 6HNO₃ → 2Al(NO₃)₃ + 3H₂O
What will SiO₂ act as? And what will it react with as a result?
Acts as a weak acid, reacts with a strong base (under certain conditions)
Under what conditions will SiO₂ react with strong bases?
Hot, concentrated bases (e.g. NaOH)
Equation for SiO₂ with NaOH?
SiO₂ + 2NaOH → Na₂SiO₃ + H₂O
What is the product when SiO₂ reacts with NaOH?
Sodium silicate
Are P₄O₁₀, SO₂ and SO₃ acidic or basic oxides?
Acidic
Do P₄O₁₀, SO₂ and SO₃ react with acids or alkalis?
Alkalis
What is the overall equation for the reaction of P₄O₁₀ with NaOH? (write half equations)
OVERALL: P₄O₁₀ + 12NaOH → 6H₂O + 4Na₃PO₄
(P₄O₁₀ + 6H₂O → 4H₃PO₄
H₃PO₄ + 3NaOH → Na₃PO₄ + 3H₂O x4 to cancel H₃PO₄)
What is the overall equation for the reaction of SO₂ with NaOH? (write half equations)
OVERALL: SO₂ + H₂O → H₂SO₃
(SO₂ + H₂O → H₂SO₃
H₂SO₃ + 2NaOH → Na₂SO₃ + 2H₂O)
What is the overall equation for the reaction of SO₃ with NaOH? (write half equations)
OVERALL: SO₃ + 2NaOH → Na₂SO₄ + H₂O
(SO₃ + H₂O → H₂SO₄
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O)