3.2.4 Properties of period 3 elements and their oxides Flashcards
Is sodium or magnesium more reactive?
Sodium (G1) is more reactive than magnesium (G2).
When they react they lose electrons to form Na+ and Mg2+.
Why is sodium more reactive than magnesium?
The amount of energy required to remove an outer electron from sodium is lower than it is to remove 2 electrons from magnesium. More energy is required for magnesium to react.
Explain the reaction between Sodium + water
reacts vigorously with cold water.
Forms a ball and fizzing
Gas produced is hydrogen (H2) and alkaline solution (NaOH).
Write out an equation to show the reaction of sodium with water.
2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)
Explain the reaction between magnesium and water.
reacts slowly with cold water, weak alkaline solution of Mg(OH)2 is formed = due to Mg(OH)2 being sparingly soluble = little OH- ions in solution.
Write an eqaution to show the reaction between magnesium and water.
Mg(s) + 2H2O(l) -> Mg(OH)2(aq) + H2(g)
Explain the reaction between magnesium and steam.
reacts more faster forming MgO
Write an equation to show the reaction between magnesium and steam.
Mg(s) + H2O(g) -> MgO(s) + H2(g)
When period 3 elements react with oxygen what do they form?
Oxides.
What element in period 3 is excepted with their reaction with oxygen and why?
Sulfur forms SO2 (oxidation state = +4).
With higher temperature and catalyst = oxidation state = +6
Sodium + oxygen
2Na(s) + 1/2O2(g) -> 2Na2O(s)
sodium oxide
Reaction with air: very fast
Magnesium and oxygen
Mg(s) + 1/2O2(g) -> MgO(s)
magenisum oxide
Reaction with air: Very fast
Aluminium and oxygen
2Al(s) + 1/2O2(g) -> Al2O3(s)
Aluminium oxide
Reaction with air: Slow (fast if powered as larger SA)
Silicon and oxygen
Si(s) + O2(g) -> SiO2(s)
Silicon dioxide
Reaction with air: slow
Phosphate and oxygen
P4(s) + 5O2(g) -> P4O10(s)
Phosphorous (v) oxide.
Reaction with air: Spontaneously combusts.
Sulfur and oxygen
S(s) + O2(g) -> SO2(g)
sulfur dioxide
Reaction with air: Steadily burns.
What affects the melting point of period 3 oxides?
Their structure and bonding.
Explain the structure and bonding of Na2O, MgO and Al2O3 compared to their melting points.
High melting points Na2O, MgO and Al2O3 as they form giant ionic lattices, strong electrostatic forces between oppositely charged ions, lots of energy required to overcome these bonds.
Why does MgO have a higher melting point than Na2O?
Mg forms 2+ ions and Na forms 1+ ions.
2+ ions are strongly attracted to oxygen.
Less energy needed for Na to lose 1 electron than it does for Mg to lose 2 electrons.
Why does Al2O3 have a lower melting point than MgO?
The Al3+ ions distort the electron cloud of oxygen.
Some covalent character = 3+ charge means that electrons from oxygen are pulled towards Al2.
Less energy is required to break the bonds.
Explain the structure and bonding of SiO2 compared to its melting point.
Non-metal.
Macro molecular structure = giant covalent structure formed.
Many covalent bonds.
Lots of energy required to break these bonds.
Why do P4O10 and SO2 have a lower melting point than SiO2?
They form simple molecular structures
weaker intermolecular forces
Less energy is required to break these bonds.
What are ionic oxides?
Na and Mg form alkaline solutions when added to water.
Contain O2- ion which accepts protons from the water molecule when dissolved in solution.
Sodium oxide + water
Na2O(s) +H2O(l) -> 2NaOH(aq)
sodium oxide readily dissolves in water to form alkaline solution = NaOH. pH 12-14.
Magnesium oxide + water
MgO(s) + H2O(l) -> Mg(OH)2(aq)
Magnesium oxide dissolves sparingly in water so alkaline solution formed (pH = 9-10) is not as strong as sodium oxide (pH = 12-14)
What are simple covalent oxides?
form acidic solutions when added to water. (P and S)
Form solutions with a pH of 0-2 (assuming minimum concentration of 1moldm-3)
Phosphorous oxide + water
P4O10(s) + 6H2O(l) ->4H3PO4(aq)
H3PO4(aq) -> 3H+ + PO4^2-
Phosphoric acid
sulfur dioxide + water
SO2(g)+ H2O(l) -> H2SO3(aq)
H2SO3(aq) -> 2H+(aq) + SO3^2- (aq)
sulfuric acid / sulfurous acid
Sulfur trioxide and water
SO3(l) + H2O(l) -> H2SO4(aq)
H2SO4(aq) -> 2H+ + SO4^2-(aq)
sulfuric (VI) acid
OS of sulphur = +6
Silicon dioxide and water
Insoluble
Have giant covalent structures = strong covalent bonds = large amount of energy to overcome bonds = why silicion dioxide is insoluble in water.
Will react with base to form salt = so classed as acid.
Aluminium oxide and water
Insoluble
Amphoteric will react with both acid and base to form salt
Has both covalent and ionic character.
What does an acid + base form?
Salt + water.
MgO(s) + H2SO4(aq) ->
MgSO4(aq) + H2O (l)
Reaction with basic oxides
2HCl (aq) + MgO (s) ->
MgCl2(aq) + H2O (l)
Reaction with basic oxides
H2SO4(aq) + NaO2(s) ->
Na2SO4(aq) + H2O (l)
Na2O(s) + 2HCl (aq) ->
2NaCl(aq) + H2O (l)
Reactions with acid oxides
2NaOH(aq) + SiO2(s) ->
Na2SiO3(aq) + H2O(l)
sodium silicate
Reactions with acidic oxides
12NaOH(aq) + P4O10(s) ->
4Na3PO4(aq) + 6H2O(l)
salt will always be phosphate and metal
if it was Potassium it would be 4K3Po4 + 6H2O
- What is phospohric acid.
- How many H+ ions can it donate?
- Outline the reaction with sodium hydroxide.
- Tribasic
- 3H+ions
- H3PO4(aq) + NaOH (aq) -> NaH2PO4(aq) + H2O (l)
* NaH2PO4 (aq) + NaOH (aq) -> Na2HPO4(aq) + H2O (l)
* Na2HPO4 (aq) + NaOH (aq) -> Na3PO4(aq) + H2O (l) - Overall Reaction: 3NaOH(aq) + H3PO4(aq) -> Na3PO4(aq) + 3H2O(l)
Reactions with acidic oxides
2NaOH(aq) + SO2(g) ->
Na2SO3(aq) + H2O (l)
Reaction with acidic oxides
2NaOH(aq) + SO2(g) ->
Na2SO3(aq) + H2O(l)
sodium sulfate
Reactions with acidic oxides.
2NaOH(aq) +SO3(g) ->
Na2SO4(aq) + H2O (l)
sodium sulfate.
Reaction with acidic oxides
2NaOH(aq) + Al2O3(s) + 3H2O(l) ->
2NaAl(OH)4 (aq)
Aluminium oxide acts as your acid.
No water produced.
Reacts with hot conc. NaOH
3H2SO4(aq) + Al2O3(s) ->
Al2(SO4)3(aq) + 3H2O(l)
