صفحه 1:
Gohubliy oP wet kydroxdes, موی لام
bekuvior.
K,= [Pe] [OW = 102°
ح4يه > رام )3( e(O'W),,
۳ [Pe] =d0" @
صفحه 2:
OP pee fewes اه له 9 له و وه شمه موه مه a
while it wil clear, cod oc prone previpitte oP Pe(OW).,(S) wil
Por. Phe extol to whick Pe? coo exis io svluicg os 0 Puocica
DP pW cad be colrutted Pro the svlubiliy product, OC, Por
e(OW),(S) the expression Por UC, is vest by:
swanky Pe po ot [OL] اس
[eK Jfoup = doe
44
9[
Ove thus Prods thot the worxtuc و() اه مه اجه ic شام
is vowed by pW, us detoiled vo the vent slice.
صفحه 3:
is obtaiced Prow انب ,6 موه و [ ]اجه عب ما و
۰ موه ما ناکم ا
OL = APO] + اه
Dh, Pike pW ts ©, tea pOW = 00, oad sv 7a. POW ts rebated
12 [OW] the sere way us PD ts rekted tm [1L*].
vb = du UP]
pO = 4n[OU] [0]
Gp, corte be powedraiva of [ Pe Ju pL OP,
we wee eqs. [9] [S] to calruate that ot pW O.P, pOW = P.O,
ov trot [OL] = 10-?9 0. This ts thea used fo equatza [C] 5
valrutate thot (Pe?) is given by:
صفحه 4:
۱ ot pL OP?
Crow te previo pare, op OP we hae [OW] = 10° 0,
Dhue, puttery [OW] = 10°" O to equation G, we vet
405 = [Pe] x ] 006/5 2 9, 6م
سم sees
40865 ۱0888 2 0
[Pe]
Qo trot Por و ما و جوا و د امنود ب a std
hydroxide previptate D(O1V),, the equation hus te [OL] raised to
te power u. Por exnvple!
Pb?" Pores PLOW) ,(8); K, = dD" = [Pb] [OW]?
DRE Pores THO) (8): K,, = dD? = [DK] [OW]?
صفحه 5:
مه ۲ [ ۲ج ماه وه موم Oroblew: Oket ts the
GO.) 2 :4 بها) 6.۶ با ه مفاوه
5, عع - )0 د ركهم 0.6 لام - 6.6.
Dh, [OW] = (08° @, oo we eve?
0 ۲ = ول
[PR] x D998 = ول
AD L82 مان = [TRY]
= dos @
صفحه 6:
Cuvtors trot pooirol the svlubiiy oP او
hydroxtdes.
his Poured that CC, ts, the p(X, Por aque ious, 0 Puartioa oP etal
vu size, chore, vod elerirooeyativiy. Mus, Peo? ts a seed io oP
Reidy high chore, cod optioo-low elevircaryaivipy, on sv Pos a
لوا oF low svhubiliy. Thus, the hydroxide oP Dat, which is
OxOW, is highly svhuble to woter, Lhe of the ver extrewe,
PuOW) (9) 5 oF very law sohubliy (AC, = (D928), Mie batter
Pact is Portucaie, becouse the high) rediartive Pu(10) is wt
readily tecosported to wouter, stave it exists us u previpitated
hydronide. Exacples of the ePPert oP charge oo svbubtlipy oF
hydroxides ore?
Cy Oet ba DR
by: “RP 06.0 20.9 20
صفحه 7:
QOetd oxides coo be regarded sicoply as dehydrated hydroxides.
QOetd hydroxides coo usudly be heoted to qive the oxides, اه
sowettves very high te;wperdures ure required:
SOHOW)() = PLOgle) + (و)ممنكهة
01
اه بو wolves suck مومس که ولو( ۳
wetdl sults ه دز hit, with woters oP hydration beta dived oPP.
Phe oxides tewd t7 be tess svluble thos the Preshiy previpitcted
hydroxides, ood oo stoodicg تومب hydroxides lose woter, ord
‘age’. Dkus, aged previpitates oP hydroxides: oa be work less
soluble thoa Preshly previpioied hydroxides. Presk ‘CxO’ ts quite
uxter svluble, but od sacoples coc be hight tosvluble.
صفحه 8:
Qvwphvterc bekwior.
Okeu vor locks of the periodic table, coe Prods thot of the very fet,
wwetd oxides ore busic. Mot wecas thot iP they ore dissolved it
voter, they شمه نو جر
@u,O (s) +0 (J) = © Ost (ag) + © OW (aq)
1
On the right hod side, wetdl oxides dissvlue to que لته
soluiives, us wit توا مان
6O,(s) + 1,0 () = 8 Wt (ag) + GO,° (aq)
[9]
kere iso trocstivod aced where the wetds ooo display boty
besic ced acidic behavior. Mhis is coled coarphoteric behavior.
صفحه 9:
@wphwteric bekwior ه )9۱۲۹( ta wqueves svhuiod!
(111) ceo display bot onidic properties ood basic properties!
مه ماه واه
9ه) [م()0] 2 (29) 0٩ 5 + (دارصیل :حدم
[9
®usic: @l,O.(s)+ O W* (ag) Be [P(OW,),])°* (aq)
[do] ۷
hexouqua ckenioc(111) cao
Ot kick pW @l,Og ts بحطصت White of low pL itis basic. Me roe
oP extsteure of the spevies [BIW .O),)°*, [Pl(W,0).(OW)]**,
ued [POW ).) te show to the species distributiva میج below:
صفحه 10:
Gpevies dstribuicg draco Por B11) to aqueres
شاد
۱ =
PAD roage = rere
where POW), (8)
تمص سخا مهو
( ملام م :4 ]
۳
0۳
() و060
Md
96 oP @ av epevies shows
و 2 8 8 8 8 8 2 8 8
o 9 do de
صفحه 11:
Oxophotertc wetd ious te the period
table:
QDerd ous frat ore exophoterty tn he period table ore ها لجع لكالا
‘Dove oP anphoierio wetd ion
0
Gc
Ge®r
Ob De
("1")
سام
Po
Dhe spevies Porcwed ut high pW are, Por exavple, the tetrahedral
exe [Be(OW),P زره یناما I,
cred [‘Fa(OL) , F-
Solubility of metal hydroxides, and amphoteric
behavior.
Kso= [Fe3+] [OH-]3 = 10-39
Fe(OH)3 (s)
precipitate
pH = 6.4
[ Fe3+ ] = 10-16 M
Solubilities of metal hydroxides.
If one leaves an orange solution of a ferric salt to stand, after a
while it will clear, and an orange precipitate of Fe(OH)3(s) will
form. The extent to which Fe3+ can exist in solution as a function
of pH can be calculated from the solubility product, Kso. For
Fe(OH)3(s) the expression for Kso is given by:
maximum Fe3+ conc at [OH-] indicated
Kso =
[Fe3+] [OH-]3 =
10-39
[2]
One thus finds that the maximum concentration of Fe3+ in solution
is controlled by pH, as detailed on the next slide.
Note that we need [OH-] in expression 2, which is obtained from the
pH from equation 3.
[3]
pKw
=
pH
+
pOH
= 14
Thus, if the pH is 2, then pOH = 12, and so on. pOH is related to
[OH-] in the same way as pH is related to [H+].
pH
pOH
=
=
-log [H+]
-log [OH-]
[4]
[5]
So, to calculate the maximum concentration of [ Fe3+ ] at pH 6.4,
we use eqs. [3] to [5] to calculate that at pH 6.4, pOH = 7.6, so
that [OH-] = 10-7.6 M. This is then used in equation [2] to calculate that
[Fe3+] is given by:
Problem. What is the maximum [Fe3+] at pH 6.4?
From the previous page, at pH 6.4 we have [OH-] = 10-7.6 M.
Thus, putting [OH-] = 10-7.6 M into equation 2, we get:
10-39
= [ Fe3+ ] x [ 10-7.6 ]3
= 3 x -7.6
[ Fe3+] = 10-39 / 10-22.8 = 10-16 M
Note that for a metal ion Mn+ of valence n that forms a solid hydroxide
precipitate M(OH)n, the equation has the [OH-] raised to the power n.
For example:
Pb2+ forms Pb(OH)2(s): Kso = 10-14.9 = [Pb2+] [OH-]2
Th4+ forms Th(OH)4(s):
Kso = 10-50.7 = [Th4+] [OH-]4
Problem: What is the maximum concentration of [Th4+] in aqueous
solution at pH 4.2? (log Kso = -50.7)
At pH 4.2 pOH = 14 – 4.2 = 9.8.
Thus, [OH-] = 10-9.8 M, so we have:
10-50.7
=
[Th4+] [10-9.8]4
10-50.7
=
[Th4+] x 10-39.2
[Th4+]
=
10-50.7 / 10-39.2
=
10-11.5 M
= -50.7 – (39.2)
Factors that control the solubility of metal
hydroxides.
It is found that Kso is, like pKa for aqua ions, a function of metal ion
size, charge, and electronegativity. Thus, Fe3+ is a small ion of fairly
high charge, and not-too-low electronegativity, and so forms a hydroxide
of low solubility. Thus, the hydroxide of Na+, which is NaOH, is
highly soluble in water, while at the other extreme, Pu(OH)4(s) is of
very low solubility (Kso = 10-62.5). The latter fact is fortunate, because
the highly radioactive Pu(IV) is not readily transported in water, since it
exists as a precipitated hydroxide. Examples of the effect of charge on
solubility of hydroxides are:
Ag+
Cd2+
La3+
Th4+
log Kso:
-7.4
-14.1
-20.3
-50.7
Metal oxides and hydroxides.
Metal oxides can be regarded simply as dehydrated hydroxides.
Metal hydroxides can usually be heated to give the oxides, although
sometimes very high temperatures are required:
2 Al(OH)3(s)
[6]
=
Al2O3(s) + 3 H2O(g)
The formation of ceramics involves such firing of hydrated
metal salts in a kiln, with waters of hydration being driven off.
The oxides tend to be less soluble than the freshly precipitated
hydroxides, and on standing many hydroxides lose water, and
‘age’. Thus, aged precipitates of hydroxides can be much less
soluble than freshly precipitated hydroxides. Fresh ‘CaO’ is quite
water soluble, but old samples can be highly insoluble.
Amphoteric behavior.
When one looks at the periodic table, one finds that at the very left,
metal oxides are basic. That means that if they are dissolved in
water, they give basic solutions:
Na2O (s) + H2O (l) = 2 Na+ (aq) + 2 OH- (aq)
[7]
On the right hand side, metal oxides dissolve to give acidic
solutions, as with sulfur trioxide:
[8]
SO3(s) + H2O (l) = 2 H+ (aq) + SO42- (aq)
There is a transitional area where the metals can display both
basic and acidic behavior. This is called amphoteric behavior.
Amphoteric behavior of Al(III) in aqueous solution:
Al(III) can display both acidic properties and basic properties:
tetrahydroxy aluminate anion
Acidic: Al2O3(s) + 2 OH- (aq) 2 [Al(OH)4]- (aq)
[9]
Basic: Al2O3(s) + 6 H+ (aq) 2 [Al(OH2)6]3+ (aq)
[10]
hexaaqua aluminum(III) cation
At high pH Al2O3 is acidic, while at low pH it is basic. The
range of existence of the species [Al(H2O)6]3+,
[Al(H2O)5(OH)]2+, and [Al(OH)4]- is shown in the species
distribution diagram below:
Species distribution diagram for Al(III) in aqueous
solution:
Al (III) sp eci es d i st ri b u t i o n
pH range = range
100
% o f Al a s sp eci es sh o wn
cross-hatched
90
where Al(OH)3 (s)
80
precipitate forms
70
(pH ~ 4 to pH~9)
Al 3+
Al3+
60
Al (OH)2+ [Al (OH)4]-
Series1
Series2
Series3
50
soluble
40
soluble
Al(OH)3 (s)
30
20
insoluble
10
0
0
5
10
pH
15
Amphoteric metal ions in the periodic
table:
Metal ions that are amphoteric in the periodic table are highlighted in
red below:
Zone of amphoteric metal ions
Be(II)B(III)
C
N
O
F
Mg(II)Al(III)
Si
P
S
Cl
Zn(II)Ga(III)
Ge
As
Se
Br
Cd(II)In(III)
Sn (II) Sb
Te
I
Hg(II)
Tl(III)
Pb(II) Bi(III)
Po
The species formed at high pH are, for example, the
tetrahedral ions [Be(OH)4]2-, [Zn(OH)4]2-, [Al(OH)4]-,
[Ga(OH)4]-, and [In(OH)4]-.
