oxides Flashcards
(34 cards)
how to distinguish bw Na2O and P4O10
- react w water
- us elimus paper -> Na2O = blue as alkaline; P4O10 = red as acidic
eqn for reaction of SO3 + KOH
SO3 + 2KOH- -> K2SO4 + H2O
eqn for reaction of excess MgO w H3PO4
3MgO + 2H3PO4 -> Mg3(PO4)2 + 3H2O
how does Na react w o2
- yellow flame
- white solid produced
how does mg, al, is, p react w o2 observations
burn with a white flame to give white solid smoke.
how does s react w o2 observations
burns with a blue flame to form an acidic choking gas
how’s Na + P stored
Sodium is stored under oil and phosphorus under water to stop these elements coming into contact and reacting with air.
how to prove that the metal oxides contain ions experimentally
melt the solids and show they conduct electricity
how do MPs change w P3 oxides
The metal oxides (Na2O, MgO, Al2O3) are ionic. They have high melting points. They have ionic giant lattice structures: strong forces of attraction between oppositely charged ions : higher mp. They are ionic because of the large electronegativity difference between metal and O
The increased charge on the cation makes the ionic forces stronger (bigger lattice enthalpies of dissociation) going from Na to Al so leading to increasing melting points.
SiO2 is macromolecular: It has many very strong covalent bonds between atoms. High energy needed to break the many strong covalent bonds – very high mp +bp
P4O10 (s), SO2 (g) are simple molecular with
weak intermolecular forces between molecules (van der waals + permanent dipoles) so have lower mp’s. They are covalent because of the small electronegativity difference between the non-metal and O atoms. P4O10 is a molecule containing 4P’s and 10 O’s. As it 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.
does al2o3 show covalent character?
Al2O3 is ionic but does show some covalent character. This can be explained by the electronegativity difference being less big or alternatively by the small aluminium ion with a high charge being able to get close to the oxide ion and distorting the oxide charge cloud.
how is al metal protected from corrosion in moist air
Aluminium metal is protected from corrosion in moist air by a thin layer of aluminium oxide. The high lattice strength of aluminium oxide and its insolubility in water make this layer impermeable to air and water.
Metal ionic oxides tend to react with water to form
hydroxides which are alkaline
r the ionic oxides basic or acidic
The ionic oxides are basic because the oxide ions accept protons to become hydroxide ions in this reaction (acting as a Bronsted-Lowry base)
na2o + h20 eqn, ph?
Na2O (s) + H2O (l)2Na+ (aq) + 2OH- (aq) pH 13 (This is a vigorous exothermic reaction)
ego + h20 eqn, ph?
MgO (s) + H2O (l)Mg(OH)2 (s) pH 9
Mg(OH)2 is only slightly soluble in water as its lattice is stronger sofewerfreeOH- ionsareproducedandsolowerpH.
al2o3 + sio2 + h20 resulting pH
Al2O3 and SiO2 do not dissolve in water because of the high strength of the Al2O3 ionic lattice and the SiO2 macromolecular structure, so they give a neutral pH 7
State and explain trend in électronégatives across P3 from Na -> S (4)
- E increases
- proton number increases
- same no. Of electron shells
- attraction if bond pair to nucleus increases
MgO is better than NaOH for treating acid in rivers and the stomach
as it is only sparingly soluble and weakly alkaline so using an excess would not make the water excessively alkaline.
Eqn for acid base reaction that occurs when Na2O reacts with P4O10 in absence if water
6Na2O + P4O10 -> 4Na3PO4
P4O10 (s) + 6 H2O, ph
P4O10 (s) + 6 H2O (l) 4 H3PO4(aq) pH 0 (this is a vigorous exothermic reaction)
SO2 (g) + H2O (l) eqn, ph
SO2 (g) + H2O (l) H2SO3 (aq) pH 3 (weak acid) SO2 + H2O H+ + HSO3-
SO3 (g) + H2O (l) eqn, ph
SO3 (g) + H2O (l) H2SO4 (aq) pH0
SO3 + H2O H+ + HSO4-
trend in oxides being acidic/basic/amphoteric
The trend is the ionic metal oxides show basic behaviour and the non-metal covalent oxides show acidic behaviour. The slightly intermediate nature of the bonding in aluminium oxide is reflected in its amphoteric behaviour: it can act as both a base and an acid
what do the basic oxides react w to form? give example eons of na2o + mgo
The basic oxides react with acids to make salts + water
Na2O (s) + 2 HCl (aq)2NaCl (aq) + H2O (l)
Na2O (s) + H2SO4 (aq)Na2SO4 (aq) + H2O (l)
MgO (s) + 2 HCl (aq)MgCl2 (aq) + H2O (l)
Or ionic equations
Na2O (s) + 2H+ (aq)2 Na+ (aq) + H2O (l)
MgO (s) + 2 H+ (aq)Mg2+ (aq) + H2O (l)
