ANSWERS TO EXERCISES AND REVISION QUESTIONS11.5One mole of calcium oxalate dissolves in water
producing an equal concentration of calcium and oxalate
ions:
Ks(Ca(C 2 O 4 ))[Ca^2 +(aq)] [C 2 O 42 – (aq)][Ca^2 +(aq)]^2
(4.47 10 –^5 )^2 2.00 10 –^9 mol^2 dm–^6
11.6
[drug in octanol] [drug in water] 1000
0.01 1000 10 mg dm–^3 of wall
(We are assuming that octanol behaves similarly to the
lipids in the stomach wall.)
11.74.6 m^3 4600 dm^3. This volume of gas contains
4600/22.4205 mol of Cl 2. Since 1 m^3 1000 dm^3 ,
the concentration of gas is
moles of gas/volume of solution
205/1000 0.21 mol dm–^3.
11.8The molar concentration of O 2 at 0 °C is
14.6
1000 32 4.6^10– (^4) mol dm– (^3) O 2
The volume of O 2 at 0° C is 22.4 4.6 10 –^4
0.0100 dm^3 or 10.0 cm^3 O 2.
Similarly at 30 ° C, the molar concentration of O 2 is
7.6
1000 32 2.4^10
– (^4) mol dm– 3
Therefore, the volume of O 2 at 30 °C is
24.9 2.4 10 –^4 0.0060 dm^3 or 6.0 cm^3 O 2
11.9 (i)5.0 10 –^3 mol dm–^3 5.0 mol m–^3
cRT
5.0 8.3145 298 12 400 Pa ( 0.12 atm)
(ii)
PnRTV cRT5.08.3145 298 12 400 Pa
In other words, the osmotic pressure of an ideal solution
(ideal means that it obeys cRT) is the same as the
pressure of an ideal gas at the same pressure and
temperature.
11.10 (i)0.0175 atm 1773 Pa
c/RT1773 / (8.3145 298)
c0.716 mol m–^3 7.16 10 –^4 mol dm–^3
c 2 c 1 c
Since the osmotic pressure was measured against pure
solvent,c 1 0. Therefore,
c 2 concentration of polystyrene
7.16 10 –^4 mol dm–^3
moles of polystyrene volume molar concentration
0.20 7.16 10 –^4
1.43 10 –^4
Molar mass mass / moles 5.0 / 1.43 10 –^4
35 000 g mol–^1.
Molecular mass of polystyrene 35 000 u.
(ii)
molesmass/molar mass
0.100/100 000 1.00 10 –^6
molar concentration 1.00 10 –^6 /1.00
1.00 10 –^6 mol dm–^3
1.00 10 –^3 mol m–^3
cRT1.00 10 –^3 8.3145 293
2.44 Pa (2.4 10 –^5 atm)
11.11Tyndall effect (see text). In soap, colloidal
particles are ionic micelles. Such particles cannot be
separated using filter paper.
11.12The vinegar produces an egg without its shell. The
outerpart of the remaining egg is a semipermeable
membrane. The inner part of the egg contains protein, and
water travels across the membrane (driven by osmosis) in
an attempt to equalize concentrations. This causes the
egg to swell. In syrup, the reverse occurs – water passes
out of the egg and the egg shrinks.
Unit 12
Exercises
12A
(i)Na 2.8.1 or 1s^2 2s^2 2p^6 3s^1
K 2.8.8.1 or 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1
Rb 2.8.18.8.1 or 1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2 4p^6 5s^1
[inert gas]ns^1 wherenis a whole number greater than 1
(ii)F 2.7 or 1s^2 2s^2 2p^5
Cl 2.8.7 or 1s^2 2s^2 2p^6 3s^2 3p^5
Br 2.8.18.7 or 1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2 4p^5
I 2. 8.18.18.7 or
1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2 4p^6 4d^10 5s^2 5p^5
outer electronic structure ns^2 np^5 wherenis a whole
number greater than 1
12B
(i)No – the second ionization energy is too high.
(ii)K+has the electron arrangement of an inert gas, argon.
(iii)The second electron is nearer the nucleus and less
shielded from the nucleus by electrons in shells between
it and the nucleus. To take away a second electron would
involve ‘disruption’ of a stable octet of electrons.
12C
(i)The boiling points decrease as the group is
descended. The metallic bonds become longer and
weaker as the atoms get larger.
(ii)About 960 K.
(iii)The alkali metals have relatively large atomic radii
and their outer electrons are weakly held – the outer
electron is well shielded from the nucleus by the full
inner shells. The large atomic radii of the atoms results
in longer, weaker metallic bonding as compared with the
bonding in other metals, making them relatively ‘soft’.
(iv)The large atomic radii of the elements results in
them taking up more ‘room’ (volume), per unit mass,
than other metals. They therefore have lower densities.
12D
(i)Extremely reactive:
Fr(s)O 2 (g)FrO 2 (s)
2Fr(s)2H 2 O(l)2FrOH(aq)H 2 (g)
(ii)Fr 2 CO 3 , very soluble, very thermally stable.
(iii)Thermally the most stable. Likely to decompose to
the nitrite with strong heating:
2FrNO 3 (s)2FrNO 2 (s)O 2 (g)
12E
The metallic bonds are shorter and stronger because the
atomic radii of the Group 2 metals are smaller than
those of the corresponding alkali metals. Also two
valence electrons are released per ion, to ‘glue’ the
cations together in the structure.
12F
(i)The atom has lost its outer shell electrons and the
overall positive charge ‘pulls’ the remaining electrons
closer to the nucleus.
(ii)Although there is an increase in the positive charge
on the nucleus, the outer electrons are farther away from
the nucleus and shielded by more full shells, as the
group is descended.
(iii)The atomic and ionic radii are similar.
12G
(i)SiH 3 – SiH 2 – SiH 2 – SiH 2 – SiH 2 – SiH 3
(ii)Covalent, similar shape to ethane; each Ge atom has
four bonds arranged tetrahedrally around it.
12H
(i)
(ii)PbIIis the more stable oxidation state of lead.
(iii)Pb–H bonds are longer and weaker than C–H bonds,
because Pb is a much larger atom than C.
(iv)CO.
(v)GeO and GeO 2. You would expect GeO 2 to be the
more stable, because GeIVis the more stable oxidation
state (GeO is readily oxidized to GeO 2 in air).
12I
(i)SiCl 4 (l)2H 2 O(l)SiO 2 (s)4HCl(aq)
(ii)It is longer and weaker. Si is a larger atom than C.
12J
(i)Si–Si bonds are longer and weaker than C–C bonds.
The shared electrons can ‘jump out’ of the Si–Si bonds
more easily.
(ii)Only a small proportion of the bonding electrons are
set free; each silicon atom still has three covalent bonds
to keep it in place if one bonding electron is lost.
12K
(i)Black/dark.
(ii)Solid.
(iii)The least stable hydride with respect to
decomposition into its elements.
(iv)Would be the halogen with the least oxidizing power.
(v)At–as the largest halide ion would be the most highly
polarised – you would expect the salt to have a great deal
of covalent character.
(vi)Dark yellow or a darker colour, like orange.
12L
(i)Xe(g)2F 2 (g)XeF 4 (s)
(ii)
(iii)In XeF 4 , Xe has oxidation state 4 it would ‘prefer’
to be reduced to oxidation state 0, i.e. atoms of the
element Xe, which have a stable octet.
12M
(i)
(ii)
(iii)
Metal(ii)has the most unpaired electrons.
12N
(i)1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 (ii)1s^2 2s^2 2p^6 3s^2 3p^6 3d^4
(iii)7, MnO 4 –.
12O
(i)Sc^3 +has no d electrons.
(ii)Zn^2 +has a full subshell of d electrons – there are no
‘gaps’ for d electrons to be promoted.
12P
(i) 2
(ii)[CuCl 4 ]^2 –
(iii) 4
(iv)tetrachlorocuprate(II).
12Q
- (i)hexacyanoferrate(III)
(ii)tetraamminezinc(II)
(iii)hexaaquatitanium(III)
(iv)tetraamminediaquacopper(II)
(v)pentaamminebromocobalt(III)
(vi)diamminetetrachloroplatinum(IV) - (i)[PtCl 6 ]^2 –
(ii)[Cr(H 2 O) 4 Cl 2 ]+
(iii)[Pd(CN) 6 ]^2 –
(iv)[CoBr 4 ]^2 –
(v)[Fe(H 2 O) 6 ]^3 +
3d 4s[Ar] Diamagnetic3d 4s[Ar] Paramagnetic3d 4s[Ar] ParamagneticXeF Octahedral with
respect to the
electron pairs
F around XeF FSn Sn2+ClCovalent IonicClCl 2- Cl Cl
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