Period 3 Oxides Flashcards
(21 cards)
Reaction with sodium and water
• Reaction of sodium with water
- Sodium metal reacts vigorously with water.
- A small piece is cut and added to a trough of water.
Observations:
- sodium floats on water (lower density),
- moves on surface of the water and fizzes (H2 being made and propels across water)
- metal melts (very exothermic and vigorous) forming a silvery ball.
- It eventually disappears and solution remains is colourless.
..
The equation for the reaction is:
2Na + 2H20 → 2NaOH + H2
> The solution remains has Na+ and OH- ions and has alkaline pH.
> The more Na+ added, higher pH.
.
Reaction with magnesium and water / steam
- Mg metal reacts very slow w water.
- A magnesium ribbon piece produces a small vol of H2
> when left in contact w water for several weeks.
The equation for the reaction is:
Mg + 2H20(l) → Mg(OH)2 + H2
- The solution remains has Mg2+ ions and OH- ions;
- slightly alkaline pH (just above 7).
..
- Magnesium reacts vigorously with water vapour at temps above 100 °C
- in the absence of air.
- Heating damp mineral wool generates water vapour
- drives the air out the boiling tube.
carried out like DIAGRAM 1
Observations:
- The magnesium burns with a bright white light
- and a white solid is formed.
Mg + H20(g) → MgO + H2
> The white solid formed is magnesium oxide.
Sodium oxide structure and how its formed
• Na2O is an ionic, basic oxide.
• lonic bonding; electrostatic attraction between +/-ions.
• white solid wch w ionic lattice structure.
Sodium oxide has high mp (1275°C)
> ionic lattice and there are strong forces of attraction between ions
> require a large amount of energy to break.
..
• Formation of sodium oxide
- can be formed from the reaction between sodium and oxygen.
4Na + O2 → 2Na2O
- A yellow flame is observed and a white solid is formed.
- will also be some sodium peroxide formed, Na2O2.
>contains peroxide ion, O2 -2; a highly reactive compound.
-
- Sodium metal reacts spontaneously when exposed to air.
- so (like all alkali metals) stored under oil to prevent it reacting with air.
- alkali metals are soft metals; can be cut w knife exposing shiny surface.
- The shiny surface tarnishes (goes dull) rapidly.
What are some reactions with Na2O
• Reactions of sodium oxide
- reacts with water
- produces colourless solution of sodium hydroxide; alkaline (pH 12-14).
»Na20 + H20 → 2NaOH
can be written to show ions formed:
»Na20 + H20 → 2Na+ + 20H-
- basic so reacts with acids
- producing salt and water.
»Na20 + 2HCl → 2NaCl + H20
»Na20 + H2SO4 → NaSO4 + H20
- - Sodium oxide dissolves in water
- oxide ion acts as base; accepts H+
- from water or acid:
with water:
»O2- + H20 →20H-
with acids:
» O2- + 2H+ → H20
How is magnesium oxide formed? And its structure
• MgO is an ionic, basic oxide.
• Its bonding is ionic. (electrostatic attraction between +/- ions)
• a white solid w a ionic lattice structure.
MgO has high mp (2852°C)
>as consists of ionic lattice and are strong forces of attraction between
> which require a large amount of energy to break.
>
>The mp of magnesium oxide is substantially higher sodium oxide
>as Mg2+ is smaller w higher charge
> The electrostatic forces of attraction between the Mg2+ ions and O2- ions are hence stronger.
..
• Formation of magnesium oxide
- Magnesium oxide can be formed from reaction w magnesium and oxygen.
»2Mg + 02 → 2Mg0
- Magnesium burns in air.
- white light observed; white solid formed.
Reactions of magnesium oxide
- Magnesium oxide is slightly soluble in water
- some does react
»MgO + H20 → Mg(OH)2
- - The pH of solution of magnesium oxide is slightly alkaline, round pH 9
- due to magnesium oxide is slightly soluble
- only some of oxide ions dissolve and react w water producing OH-
..
- basic so reacts with acids making a salt and water.
» MgO + 2HCl → MgCl2 + H20
» MgO + 2HNO3 → Mg(NO3)2+ H20
The oxide ion accepts protons from the acid to form water:
02-+ 2H+ → H20
Whats the structure of aluminium oxide and hows it formed
• Al2O3 is an ionic, amphoteric oxide.
• its bonding is ionic; the electrostatic attraction between +/- ions.
• a white solid wch has ionic lattice structure similar to other p3 metals
• melts at 2072°C; high mp caused by strong electros. attraction between ions.
..
• Formation of aluminium oxide
- can be formed from reaction between powdered Al and O2.
» 4A1 + 3O2 → 2Al2O3
-
- A white solid is formed.
- Al powder reacts readily but Al foil doesnt react as easily
- as has a protective oxide layer that prevents reaction.
- This layer also protects Al from reaction w water
->so preventing corrosion.
What are reactions of aluminium oxide
- Aluminium oxide does not dissolve in water or react with water.
- due to strength of ionic bonds between opposite charge small ions.
- mixture of Al2O3 and water has pH 7 as does not react w water.
- Aluminium oxide is amphoteric as reacts w both acids and bases:
- General equations:
> W acid: Al203 + 6H+ = 2Al3+ + 3H20
> W base: Al203 + 20H- + 3H20 = 2AI(OH)4 - (aluminate ion formed)
..
Example :
» w HCl: Al203 + 6HCl + 2AlCl3 + 3H20
» w NaOH: Al203+ 2NaOH + 3H2O → 2NaAl(OH)4
What happens if a basic oxide reaxts with phosphoric acid
Basic oxides also react with phosphoric(V) acid, H3PO4.
> The same phosphate(V) salt is formed (ion is PO4 3-
> but water is also formed.
3Na2O + 2H3PO4 → 2Na3PO4 + 6H20
3MgO + 2H3PO4 → Mg3(PO4)2 + 3H20
Why do basic properties exist in metallic oxides
The basic properties of the metallic oxides of Period 3 elements
> due to presence of oxide ion, 02-, wch can act as base and accept a proton, H+
What are the bonding, propetries and structures of sulfur oxides
• Sulfur forms two oxides,
-sulfur(IV) oxide (sulfur dioxide)
-sulfur(VI) oxide (sulfur trioxide).
»Both are covalent acidic oxides.
- Sulfur dioxide is SO2
- sulfur trioxide is SO3.
• The bonding in both is covalent.
• The structure of both is molecular (simple covalent).
• Sulfur dioxide is colourless gas (mp -73 °C) with pungent odour.
•
• appears as misty fumes in most air due to reaction w moisture in air.
• Sulfur trioxide is a colourless liquid (mp 17°C).
..
The structure of both is described as molecular covalent.
> SO2 is bent, 119°, polar
> SO3 is trigonal planar,120°, non polar
Howre sulfur oxides formed
• Sulfur burns in air; yellow solid sulfur melts
• to form a red liquid wch burns w a blue flame
»forming misty fumes of a choking and pungent gas.
» S + O2 → SO2
• Sulfur dioxide can be converted to sulfur trioxide
• on reaction w more oxygen in the presence of a vanadium(V) oxide
• (a catalyst) under specific conditions.
2SO2 + 02 → 2S03
What are Reactions of the oxides of sulfur
Sulfur dioxide reacts w water producing sulfuric(IV) acid, H2SO3
> also called sulfurous acid.
» SO2 + H20 → H2SO3
>
Solution formed when sulfur dioxide reacts w water is weak acidic.
- due to reaction being reversible position of eq. being to the left
» SO2 + H20 = H+ + HSO3
..
SO3 reacts very vigorously w water making sulfuric (VI) acid, H2SO4.
» SO3 + H20 → H2S04
- As both sulfur dioxide and sulfur trioxide are acidic oxides,
- they react with bases.
- Sulfur dioxide reacts w bases forming sulfate(IV) ions SO3 2-.
- also called the sulfite ion
-
- Sulfur trioxide reacts w bases forming sulfate(VI) ions; SO4 2-
- is called the sulfate ion.
General equations:
SO2 + 20H- → SO3 2- + H20
SO3 + 20H- → SO4 2- + H20
> adding metal ion to reactants will give the balanced symbol equation:
»SO2 + 2NaOH → Na2SO3+ H20
» SO3 + 2KOH → K2SO4 + H20
Why are boiling points higher in SO3 than SO2, though SO2 is polar
P4O10 melts at 300°C
SO2 melts at - 73°C.
SO3 melts at 17°C
- All three of these substances are molecular covalent.
- P4O10 has higher mp than others as is a larger molecule w more electrons
- so the vdw forces between molecules are greater
- more energys required to overcome attraction forces between molecules.
-
- SO3 is larger than SO2 so mp is higher due to larger vdw forces
- between SO3 mols than SO2,
- even though SO2 is polar and SO3 is non-polar.
What are all the reactions of P3 oxides with water ??
DIAGRAM 2
Memorise all pls 🙏🥹
Whats the trends in melting points of P3 oxides (metal oxides)
For metal oxides (Na2O, MgO and Al2O3)
- in general, the mp increases as charge on metal ions increases
- as size of metal ion decreases.
> ionic compounds w smaller ions and higher charge ions have highest mp.
> > explains increase in mp from Na2O to MgO
BUT mp of Al2O3s lower than MgO.
As Al2O3 has a high charge density so polarises lectrons in oxide ion
has degree of covalent character so reduces the melting point.
Whats the trends in melting points of P3 oxides (non metallic)
- SiO2 has a macromolecular (giant covalent structure)
- and so a large amount of energys required to break
- ## the many strong covalent bonds to melt it.
- P4O10 and SO3 are molecular in structure.
- P4O10 has a higher Mr than SO
- so has stronger vdws’ forces of attraction between the molecules
Whats the structure of acids phosphoric acid
When acidic oxides react with water they form oxyacids.
- These oxyacids are covalent compounds
- wch form ions in aq solution.
• Phosphoric acid
- Food-grade phosphoric acid is used to acidify foods; eg colas.
- provides a tangy and sour taste.
• When P4O10 reacts with water, phosphoric(V) acid, H3PO4s formed.
• The (V) is the oxidation state of phosphorus atom (+5)
•
• Phosphorus atoms promote electrons into 3d sub-shell
• so can to form five covalent bonds.
• The shape around phosphorus atom is tetrahedral (109,5°)
Whats the structure of anions of phosphoric acid
..
- The 3 H atoms are acidic as theyre bonded to electronegative
- oxygen atoms and so can be donated as H+ ions.
-
- Phosphoric acid is a triprotic acid; forms 3 anions as H+ leave
- molecule on reaction w bases.
»NaOH + H3PO4 → NaH2PO4 + H2O
- NaH2PO4 is sodium dihydrogenphosphate(V).
- The H2PO4 ion is the dihyrogenphosphate(V) ion.
> > 2NaOH + H3PO4 → Na2HPO4 + 2H2O
- Na2HPO4 is sodium hydrogenphosphate(V).
- HPO2 is hydrogenphosphate(V) ion.
> > 3NaOH + H3PO4 → Na3PO4 + 3H2O
- Na3PO4 is sodium phosphate(V).
- PO4 3- is phosphate(V) ion.
> All ions shown have tetrahedral shape
with a 109.5° bond angle.
with a double bonded O at the top with P
Whats the structure of acids and anions (sulfuric acid IV)
• When SO2 reacts with water, sulfuric(IV) acid, H2SO3 is formed.
• The (IV) refers to oxidation state of S atom (+4)
•
• Sulfur atoms in H2SO3 promote one electron into 3d sub-shell
• so can form four covalent bonds. The S atom has a lone pair of electrons.
• The shape round S atom is pyramidal (bond angle 107.5º)
..
- Sulfuric(IV) acid forms 2 diff salts on removal of one or both of H atoms as H+ ions.
» NaOH + H2SO3 → NaHSO3 + H20 - NaHSO3 is sodium hydrogensulfate(IV).
- The HSO3 - ion is the hydrogensulfate(IV)/sulfite ion
> > 2NaOH + H2SO3 → Na2SO3 + 2H20
- Na2SO3 is sodium sulfate(IV).
- The SO3 2- ion is the sulfate(IV)/sulfite ion.
How is the structure for acids and anions (sulfuric acid VI)
• When SO3 reacts w water, H2SO4, is formed.
• The (VI) refers to oxidation state of S atom (+6)
•
• Sulfur atoms in H2SO4 promote two electrons into 3d sub-shell
• so to form six covalent bonds.
• The shape round S atom is tetrahedral ( 109.5º)
..
Sulfuric(VI) acid forms 2 diff salts on removal of 1/2 H atoms as H+ ions.
» NaOH + H,SO4 → NaHSO4 + H20
- NaHSO4 is sodium hydrogensulfate(VI).
- The HSO4 ion is hydrogensulfate(VI) ion
> > 2NaOH + H2SO4 → Na2SO4 + 2H20
- Na2SO4 is sodium sulfate(VI).
- The SO4 2- ion is sulfate(VI) ion
