Properties of Period 3 elements and their oxides (A-level) Flashcards
What is the reaction of Na with cold water?
2NA(s) + 2H20(l) –> 2NaOH (aq) + H2(g)
Reaction of Magnesium with water
Mg(s) + 2H2O(l) —> Mg(OH)2(s) + H2(g)
Reaction of Magnesium with steam
Mg(s) + H20 —> MgO(s) + H2(g)
Describe the reactions of elements in Period 3 (up to sulphur) with oxygen
Na - burns with yellow flame to produce a white solid
Mg, Al, Si and P - burn with white flame + white solid smoke
S - burns with Blue flame to form acidic choking gas
Equation: Na with oxygen
4Na + O2 —> 2 Na2O
Equation: Mg + O2
2Mg + O2 –> 2MgO
Equation: Al + O2
4AL + 3O2 –> 2Al2O3
Equation: Si + O
Si + O2 –> SiO2
Equation: P + O2
4P + 5O2 —> P4O10
Equation: S + O2
S(s) + O2 —> SO2(g)
How can we stop elements such as sodium and phosphorus from coming into contact and reacting with air?
Storing under oil and phosphorus under water
Describe the trend in melting points from Na-S
Ionic oxides - Na2O, MgO, Al2O3
- high melting points.
- ionic giant lattice structures:
-strong forces of attraction between oppositely charged ions : higher mp.
- increased charge on the cation makes the ionic
forces stronger going from Na to Al so increased melting points.
Macromolecular oxides - SiO2
- macromolecular:
- many very strong covalent bonds between atoms.
- High energy needed to break the many strong covalent bonds – very high mp
Simple molecular oxides: P4O10 (s), SO2 (g)
- weak intermolecular forces between molecules
(van der waals + permanent dipoles)
- lower mp’s.
- P4O10 is a bigger molecule and has more electrons than SO2 it will have larger van der waals forces between molecules and a higher melting point.
Why do ionic oxides react with water?
They accept H+ ions to become OH- ions acting as a Bronsdted-lowry base
Reaction + PH: sodium oxide with water
Na2O (s) + H2O (l) –> 2NaOH(aq)
pH 13
vigorous exothermic reaction
Will Na20 react with acids or alkalis, depending on which what is it’s nature?
Acids
Acid + Alkali –> Salt + H20
Na20 –> BASIC
Reaction + PH: Mg oxide with water
MgO (s) + H2O (l) –> Mg(OH)2(s)
pH 9
sparingly soluble
Why does MgO oxide produce a lower pH when reacting with water compared to Na2O?
Mg(OH)2 (the product) is a slightly soluble in water as its lattice is stronger so fewer free OH- ions are produced and so lower pH
Does Al203 react with water and explain answer?
No
high strength of the ionic lattice in Al2 O3 so gives neutral PH7
What is the reaction of aliminium oxide with acids? (use. hcl as example)
Acts as a base
Al2O3 + 6H+ —> 2Al.3+ + 3H2O
What is the reaction of aliminium oxide with alkalis?
Acts as a acid
Al2O3 (s) + 2OH-(aq) +3H20 —> 2Al(OH)4-(aq)
Does SiO2 reacts with water?
no reaction
insoluble
due to many strong covalent bonds in macromolecular structure
Reaction of SiO2 with alkalis?
SiO2 + 2OH- —> SiO3.2- + H20
What does the reaction of simple mocleular acidic oxides with bases form?
Salt + H20
Reaction and PH: P4O10 with water
P4O10 + 6H2O –» 4H3PO4
PH 0
Reaction of P4O10 with alkalis
P4O10+ 12OH- —> 4PO4.3- + 6H2O
Reaction of SO2 with alkalis
SO2(g) + 2OH- (aq) –> SO3.2- (aq) + H2O (l)
Reaction of SO2 with water + PH
H2O(l) + SO2(g) —> H2SO3(aq)
PH 3
Reaction of SO3 with water + PH
SO3 + H20 —> H2SO4
PH 0
Reaction of SO3 with alkalis
SO3(g) + 2OH- (aq) —> SO4.2- (aq) + H2O (l)
What do the products of Phosphorus oxide, Sulfur dioxide and Sulfur trioxide reacting with water have in common?
All products consist of a double bond between primary element and oxygen
Reaction of acid and base make what?
Salt + Water
True/False: Non-metal covalent oxides show acidic behaviour
TRUE
True/False: Ionic metal oxides show acidc behaviuor
False
they show basic behaviour as they accept H+ ions ot become OH- ions
