Period 3 Elements And Aqueous Chemistry Of Inorganic Ions Flashcards
How does sodium react with water? What is the equation and ionic equation?
It reacta violently, producing hydrogen and a solution of sodium hydroxide. This reaction is highly exothermic, releasing a large amount of energy. This causes the sodium to melt and heats the water
2Na(s) + 2H2O -> 2NaOH(aq) + H2(g)
2Na(s) + 2H2O(l) -> 2Na+(aq) + 2OH-(aq) + H2(g)
Sodium hydroxide is a strong base. What does this mean?
It dissolves in water, dissociating completely to give a solution containing only Na+ (aq) and OH-(aq) ions. The solution is strongly alkanine
Why is magnesium less reactive than sodium?
Magnesium has a smaller atomic radius and a higher ionic charge and it has two delocalised electrons. This results in stronger forces holding the magnesium lattice together making it less reactive
Why must magnesium be strongly heated to start it’s reaction with music?
Because the activation energy to start the reaction is high
How does the reaction between magnesium and water take place?
Water is heated to form steam which is passed over the hot magnesium. The products are hydrogen and magnesium hydroxide
How to the period 3 elements react with oxygen?
They usually forn an oxide with the period three element in its highest possible oxidation state
What happens when Na, Mg and Al are heated in oxygen and what are the equations for the reactions?
They all glow brightly and form the metal oxides
4Na(s) + O2(g) -> 2Na2O(s)
2Mg(s) + O2(g) -> 2MgO(s)
4Al(s) + 3O2(g) -> 2Al2O3(s)
What structure do the oxides of Na, Mg and Al have?
Ionic lattices
When dissolved in water what are sodium and magnesium oxides?
Basic
Aluminium oxide us amphoteric. What does this mean?
That it can act as both an acid and a base
What are the oxides of the nonmetallic elements silicon, phosphorus and sulfur?
Their oxides are molecular compounds with covalent bonding
How does white phosphorous react with oxygen?
Spontaneously catches fire and burns in air
Why does sulfur not always use it’s highest possible oxidation state when forming an oxide? (SO2 rather than SO3)
Because further oxidation from SO2 to SO3 is slow
What are the equations for the reactions of silicon, phosphorus and sulfur with oxygen and what solutions do these oxides form in water?
Si(s) + O2(g) -> SiO2(s)
4P(s) + 5O2(g) -> P4O10 (s)
S(s) + O2(g) -> So2(g)
2SO2(g) + O2(g) -> 2SO3
All these oxides form acidic solutions in water
What three three types can the bonding in the oxides of period 3 elements be grouped into and which elements are in which groups?
- ionic oxides with giant lattices: Na, Mg, Al
- covalent oxides with giant lattice structures: Si
- Covalent oxides that have small molecules
Which oxides of period 3 elements have the highest melting point and which the lowest?
Ionic oxides and macromolecules have higher melting points than simple covalent oxides
Why does MgO have a higher melting point than Na2O?
Because Mg has a higher charge so there is angreater force of attraction between the ions which leads to a stronger bond. Furthermore magnesium is smaller than sodium so will have an even stronger electrostatic force
Why does Al2O3 have a slightly lower melting ooint than MgO?
It has a greater covalent character due to the distortion of the electron densities of the ions
Why does silicon dioxide have a relatively high melting point?
Because the covalent bonds are extremely strong
Why does phosphorus (V) oxide P4O10 have a higher melting point than sulfur dioxide or trioxide?
Because it is a larger molecule so there are stronger van der waal forces of attraction between the molecules and it has a higher melting point
Why is magneisum oxide MgO only slightly soluble in water and what does this mean?
Because of its high lattice energy compared with that of Na2O. As only a snall amount of MgO dissolves, the concentration of O2- ions is low and therefore so is the concentration of OH- ions that form so the solution is only slightly alkaline having a pH of 8
Is aluminium oxide soluble in water?
No
Why is silicon dioxide SiO2 insoluble in water?
Because it is a stable macromolecyle
Why are the oxides of phosphorus and sulfur classified as acidic oxides? And what are the equations for these reactions?
Because they dissolve in water to give acidic solutions
P4O10(s) + 6H2O(l) -> 4H3PO4
SO2(g) + H2O(l) -> H2SO3 (aq)
SO3(g) + H2O(l) -> H2SO4
Draw the electron movement of the hydrolysis of covalent oxidws: phosphorys(V) and sulfur (V) oxides
Snap camera roll
Are Sulfuric acid, phosphoric acid and sulfuric(IV) acid strong or weak acids and why?
Sulfuric acid is a strong acid because it dissociates fully in an aqueous solution
Phosphoric acid and sulfuric (IV) acid are both weak acids. They do not dissociate completely in solution and exist in dynamic equilibrium
Which oxides of the period 3 elements react with acids and which with bases?
The basic oxides/ionic oxides (Na2O and MgO) react with acids and the acidic oxides/ covalent oxides (P4O10, SO2 and SO3) react with bases
What aew rhe equations for the reactions of ionic oxides with acids?
Na2O(s) + H2SO4(aq) -> Na2SO4(aq) + H2O(l)
Na2O(s) + HCl (aq) -> 2NaCl(aq) + H2O(l)
MgO(s) + H2SO4(aq) -> MgSO4(aq) + H2O(l)
MgO(s) + 2HCl (aq) -> MgCl2(aq) + H2O(l)
What are the reactions of the covalent oxides with bases? (NaOH)
P4O10(s) + 12NaOH(aq) -> 4Na3PO4(aq) + 6H2O
SO2(g) + 2NaOH(aq) -> Na2SO3(aq) + H2O(l)
SO3(g) + 2NaOH(aq) -> Na2SO4(aq) + H2O(l)
Why is aluminium oxide amphoteric?
Because it reacts with solutions of strong bases and strong acids. The bonds in aluminium oxide have both ionic and covalent properties explaining it’s amphoteric properties
What are the equations for the reactions of aluminium oxide with acids and bases?
In acid:
Al2O3(s) + 3H2SO4(aq) -> Al2(SO4)3 + 3H2O
In alkali:
Al2O3(s) + 2NaOH(aq) + 3H2O(l) -> 2NaAl(OH)4(aq)
Overall:
[Al(OH)4]- [Al(H2O)6]3+
Alkali acid
Does silicon dioxide react with acids or bases amd what’s the equation?
It reacts with hot concentrated alkaline solutions to give sodium silicate
SiO2(s) + 2NaOH(aq) -> Na2SiO3(aq) + H2O(l)
What happens when ionic compounds dissolve in water?
The lattice breaks up and the ions become free to move in solution. They become hydrated aqua ions
What charge do cations have and what end of water are they attracted to?
A positive charge. They are attracted to the negative end of polar water molecules
What charge do anions have and what end of water are they attracted to?
A negative charge. They are attracted to the positive end of polar water molecules
What is the number of water molefules in a hydration shell called?
The hydration number
What may happen to the hydration number as ions move through a solution?
It may vary
What may happen to the hydration number as ions move through a solution?
It may vary
What is the normal coordination number and geometry of the immediete hydration spheres of transition metals?
They normally have a coordinatjon number of 6 and octahedral geometry
What happens when a transition metal dissolves in water?
A lone pair of eleftrons from a water molecule forms a coordinate bond with an unoccupied d orbital of the metal ion. Water acts as a Lewis base and a Ligand and the metal ion acts as a Lewis acid
What does the hydrolysis of metal-aqua ions give?
Acidic solutions
What does the ion [Al(H2O)6]3+ do to cause the solution to be acidic?
The aluminium ion pulls electron density away from the O-H bond in the coordinated water, weakening the bond. This allows a proton (a H+ ion) to break away to form H3O+. The ion behaves as a weak acid
[Al(H2O)6]3+ + H2O [Al(H2O)5OH]2+ + H3O+
Which metal-aqua ions will behave as weak acids? What is this reaction sometimes described as?
The ones that have a +2 or +3 charge on the metal ion
Described as a hydrolysis reaction
What does tha acidity of a solution depend on?
The position of equilibrium. The further it lies to the right, the more acidic the solution (the higher the concentration of H3O+)
How can the equilibrium of an acidic solution be quantified?
By aan equilibrium constant. Ka, the dissociation constant
What are the properties of metal ions that affect the acidity of their aqua ions in solution and why does this affect them?
- the charge of the metal ion
- the size of the metal ion
The larger the charge on the metal, the greater the attraction of electrons to the oxygen, leading to the weakening of the O-H bond.
Metal ions carrying the same charge but of different sized have differing strengths of attraction for electrons in the O-H bond of water. The greater the ionic charge/size ratio the dtronger the attractions for the electrons and consequently there is more dissociation producing a more acidic solution. Overall charge is more important
What are alkalis?
Bases that dissolve in water to give solutions that contain the hydroxide ion, OH-(aq).
What do reactions of aqua ions with alkalis produce?
Insoluble metal hydroxides
What happens when hydroxide ions are added to a solution of a metal-aqua complex?
The equilibrium moves further to the right and when sufficient OH- has been added an insoluble metal hydroxide forms, it is no longer an equilibrium. The reaction is complete
What does the addition of OH- ions to a solution with copper ione produce? And what is the overall reaction for this?
Hydrated copper (II) hydroxide. It is a blue solid
[Cu(H2O)6]2+ + 2OH- -> [Cu(H2O)4(OH)2] + 2H2O
What is the colour of the precipitate when hydroxide ions react with iron ions? [Fe(H2O)6]2+
Green
What is the colour of the precipitate when hydroxide ions react with iron ions? [Fe(H2O)6]3+
Brown
What is the colour of the precipitate when hydroxide ions react with aluminium ions?
White
What happens when sodium hydroxide is added to an aqueous solution of an aluminium salt? And then what happens if dilute acid is added after this
A white precipitate of aluminium hydroxide is formed initially and as more sodium hydroxide is added the precipitate dissolves to give a colourless solution containing [Al(OH)4]- ions
[Al(H2O)6]3+ + 3OH [Al(H2O)3(OH)3] + 3H2O
White precipitate
[Al(H2O)3(OH)3] + OH- [Al(OH)4]- + 3H2O
Colourless solution
Then if dilute acid is added the reverae takes place and a white precipitate of aluminium hydroxide is formed which dissolves when more acid is added to give a colourless solution of the aluminium ion
What equilibrium makes ammonia solution alkaline?
NH3 (aq) + H2O(l) NH4+(aq) + OH-(aq)
What happens when ammonia solution is added to metal-aqua ions?
A metal gydroxide and NH4+ doems
What happens if ammonia solution is added in excess to a metal aqua-ion?
Most transition metal hydroxides react further to form soluble ammine complexes
How do metal-aqua ions with the general formula [M(H2O)6]3+ hydrolyse? And then what would happen if carbonate ions were present and there was a sufficient concentration of H3O+ ions formed?
[M(H2O)6]3+ + H2O [M(H2O)5(OH)]2+ + H3O+
The carbonate ions form carbon dioxide (when added to mixture). This is evolved as a gas, shifting the equilibrium to the right
2H3O+ + CO32- -> CO2 + 3H2O
And the [M(H2O)6]3+ ions will react to give the neutral metal hydroxide [M(H2O)3(OH)3] which forms as a precipitate.
The overall equation is:
[M(H2O)6]3+ + 3CO32- -> 2[M(H2O)3(OH)3] + 3CO2 + 3H2O
What happens when metal aqua-ions with the general formula [M(H2O)6]2+ (oxidation state +2) have carbonate ions added to them?
Solutions of these ions are only very weakly acidic, with a low equilibrium concentration of H3O+. This concentration is too low to react with a carbonate and produce carbon dioxide gas. Therefore the equilibrium is not shifted sufficiently to the right to lead to the formation of the metal (II) hydroxide. Instead the metal (II) carbonate is formed. They are not very soluble in water and precipitate in solution:
[M(H2O)6]2+ + CO32- MCO3 + 6H2O
With the aqueous M(II) ion solutions of Fe(II), green, [Fe(H2O)6]2+ and Cu(II), blue [Cu(H2O6]2+ what happens when a small amount of OH- is added?
Fe(II): green precipitate Fe(OH)2
Cu(II): pale blue precipitate Cu(OH)2
With the aqueous M(II) ion solutions of Fe(II), green, [Fe(H2O)6]2+ and Cu(II), blue [Cu(H2O6]2+ what happens when OH- is added in excess?
Neither of their precipitates dissolve
With the aqueous M(II) ion solutions of Fe(II), green, [Fe(H2O)6]2+ and Cu(II), blue [Cu(H2O6]2+ what happens when a small amount of NH3 is added?
Fe: a green precipitate forms that us easily oxidised by air and turns to brown Fe(OH)3
Cu: a pale blue precipitate forms Cu(OH)2
With the aqueous M(II) ion solutions of Fe(II), green, [Fe(H2O)6]2+ and Cu(II), blue [Cu(H2O6]2+ what happens when excess NH3 is added?
Fe: green precipitate dissolves to give pale brown solution or turns brown in air
Cu: deep blue solution, [Cu(NH3)4(H2O)2]2+
With the aqueous M(II) ion solutions of Fe(II), green, [Fe(H2O)6]2+ and Cu(II), blue [Cu(H2O6]2+ what happens when CO32- is added?
Fe: green precipitate FeCO3
Cu: green-blue precipitate, CuCO3
With the aqueous M(III) ions in solution of Fe(III), violet, [Fe(H2O)6]3+ (appears brown due to hydrolysis) and Al (III), colourless what happens when a small amount of OH- is added?
Fe: brown precipitate, [Fe(H2O)3(OH)3]
Al: white precipitate, Al(OH)3
With the aqueous M(III) ions in solution of Fe(III), violet, [Fe(H2O)6]3+ (appears brown due to hydrolysis) and Al (III), colourless what happens when excess OH- is added?
Fe: precipitate does not dissolve
Al: precipitate dissolves to form colourless solution [Al(OH)4]-
With the aqueous M(III) ions in solution of Fe(III), violet, [Fe(H2O)6]3+ (appears brown due to hydrolysis) and Al (III), colourless what happens when a small amount of NH3 is added?
Fe: brown precipitate, [Fe(H2O)3(OH)3]
Al: white precipitate, Al(H2O)3(OH)3
With the aqueous M(III) ions in solution of Fe(III), violet, [Fe(H2O)6]3+ (appears brown due to hydrolysis) and Al (III), colourless what happens when NH3 is added in excess?
Neither precipitate dissolves
With the aqueous M(III) ions in solution of Fe(III), violet, [Fe(H2O)6]3+ (appears brown due to hydrolysis) and Al (III), colourless what happens whe CO32- is added?
Fe: brown precipitate of hydroxide [Fe(H2O)3(OH)3] and CO2 evolved
Al: white precipitate of hydroxide, Al(OH)3 and CO2 evolved
