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8/11/2019 Redox Trends-qa Mark Scheme
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EXAMINATION QUESTIONS FOR REDOX REACTION, TRENDS AND QA
1. (a) Accepts electrons 1
(b) Charge on the ion (or element or atom) 1
(c) +4 1
+5 1
-3 1
(d) (i) Cu
Cu2+
+ 2e
1
(ii) O!O3e4!O 223 + +
1
(iii) O42!O3Cu"2!O3Cu 22
3 ++++
++
1[8]
5. (a) (i) #oss (o$ electrons) (1)
(ii) Oxidation state of nitrogen in NO: (+) 2 (1)
Oxidation state of nitrogen in NH+:3 (1)
(iii) %2(1) 4
(b) (i) Cl2+ 2e2Cl(1)
(ii) &O2+ 22O &O42
+ 4++ 2e
(1)
(iii) &O2+ 22O + Cl2&O42
+ 2Cl
+ 4+(1)
or 2&O4+ 2Cl etc
Ignore state symbols in equationAllow multiples of all equations
3[7]
6. (a) gains electrons (1) 1
or accepts'taes electronsAllow an electron
or just gains
or reduction is gain of electrons, but NOT OILI! e"en if
stated
#o not allow $ention of electron %air&s'
(b) (i) Oxidising agent Ag+ (1)(or Ag I)
educing agent &O2(1) (or ()I, not sul%*ur)
(ii) &O2+ 22O &O42
+ 4++ 2e
(1) (or H(O+ H
++ e
-) 3
allow e i.e. no c*arge%enalise /
-once onl0
allow -e-
on LH(
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(c) (i) *e2+
*e3+
+ e
(1)
(ii) 5 (1) (or ) or +1)
(iii) ClO3
+ ++ e
Cl
+ 32O (1)
(i,) ClO3+ ++ *e2+Cl+ 32O +*e3+(1) 4
[10]
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8. (a) ains electrons (or remo,es electrons) 1
(b) (i) +4 1
+ 1
(ii) .r 2+ 2e
2.r
1
(iii) &O2+ 22O 4++
24&O + 2e
1
(i,) .r 2+ &O2+ 22O 2.r
+ 4++
24&O 1
(c) Cl2+ 2O ++ Cl
+ OCl 1
Chloride 1 1
Chlorate(%) +1 1
(d) Chloride ions cannot reduce sulphuric acid 1&Or c*loride ions are wea2 reducing agents
Or sul%*uric acid is not a strong enoug* oxidising agent
Or sul%*uric acid is a wea2er oxidising agent t*an c*lorine'
(e) /Cl + 2&O4Cl + /&O4 1
&Allow 34l + H(OH4l + 3(O'
($) (i) .romine 1
(ii) &ulphur dio0ide 1[1#]
9. (a) %ncrease 1
an der aals $orces beteen molecules 1
%ncrease ith sie (or5ror sur$ace area etc) 1
6ore energ7 needed to brea (o,ercome) these $orces 1
&Note $ax fro$ last t*ree $ar2s if no $ention of $olecules or
$olecular'
(b) (i) .ron solution (or 7ello or orange) 1
Cl2+ 2.r 2C1
+ .r21
(ii) cream precipitate 1
.r
+ Ag+Ag.r 1
8recipitate dissol,es 1
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(iii) orange (bron) $umes (gas)9 hite $umes (or mist7 $umes)9
choing gas (an7 2) 2
(c) 2++ 2&O4+ 2.r
&O2+ .r2+ 22O (&O2and .r2(1)9 e:uation (1)) 2
[13]
10. (a) increases $rom $luorine to iodine (1)
sies o$ molecules increase (1)
(or molecules ha,e more electrons or mass o$ molecules increases)
6oL $ar2
6agnitude o$ intermolecular $orces or ,d $orces increase (1)(or more ,d $orces)
6ore energ7 re:uired to separate molecules (or particles) (1) 4
(or more energ7 to brea intermolecular $orces)or intermolecular $orces di$$icult to brea
(b) ith !aCl hite ppt (1)
soluble in ammonia (1)
note, if %%t clearl0 refers to wrong substance e.g. Na4l t*en
4./ 7 8
ith !a.r cream (or o$$ hite or biege) ppt (1)
partiall7 soluble (or insoluble) in ammonia (1)
4
ignore references to conc a$$oniaif ob"iousl0 added sil"er nitrate $ixed wit* a$$onia allow:
Na4l: no c*ange (2)
Na9r: crea$ %%t (2)
(c) o0idising abilit7 decreases $rom chlorine to iodine (or don the roup) (1)
Cl2+ 2.r
2Cl
+ .r2(1)
allow use of Na9r, H9r etc
.r2red bron (or 7ello or orange) li:uid (or solution but not solid) (1)
Cl2+ 2%2Cl+ %2(1)
allow use of Na9r etc, %enalise HI once onl0
%2bron solution ' blac solid (1)
do not allow an0 reference to %ur%le
.r2+ 2%
2.r + %2(1)
;ello'orange'red-bron'bron solution goes bron'darer bron solution'
blac solid (1) 1
7drogen sulphide 1
o0idation state 2 1
(ii) &ulphur dio0ide is a choing gas or has a pungent odour
&ulphur is a 7ello solid 1
7drogen sulphide has a smell o$ bad eggs 1
An0 $ar2s
(iii) &O42
+ 4++2e
&O2+ 22O 1
&O42
+ "++e
& + 42O 1
&O42
+ 1>++"e
2& + 42O
An0 $ar2s
&Allow euations wit* H(O'
(c) Cl2+ 2O ++ Cl
+ OCl
or Cl2+ 2O 2++ Cl
+ OCl
or Cl2+ 2O Cl + OCl
ater is not o0idised
?he o0idation states o$ O (2) and (+1) remain unchanged 3[1$]
12. (a) decreases 1
number o$ shells increases' shielding increases 'atomic sie increases 1
eaer attraction (b7 nucleus) on bonding electrons ' eaer
attraction (b7 nucleus)
on electron pair in a co,alent bond 1
(b) (i) increases 1
(ii) concentrated sulphuric acid 1
(c) hite ppt 1
soluble in ammonia 1
cream ppt 1
partiall7 soluble 'insoluble in ammonia 1
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(d) Cl2+ 2!aO @ !aCl + !aOCl +2O 1
bleach 1
disin$ectant 'steriliser'ills bacteria 1[1"]
13. (a) *luorine or *2or * (1) 1
NOT ;l
(b) %
(or At
) (1) 1
allow +e-
but not euation
(c) Obser"ation wit* Na;&a':no change O= colourless solutionO= remains colourless (1)
Obser"ation wit* NaI &a' 7ello solid ' percipitate (1)
/uation %
(a:) + Ag+(a:) Ag%(s) (1) 3
or !a% (a:) + Ag!O3(a:) !a!O3(a:) + Ag%(s)
no ss no $ar2s
(d) Obser"ation steam7 ' hite ' mist7 $umes (1)
NOT s$o2e < gas
/uation !aCl + 2&O4!a&O4+ Cl 2Ignore ss
(e) Obser"ation = blac ' gre7 solid
lilac ' purple gas
pungent ' steam7 ' choing $umes ' steam
Obser"ation 7ello solid ' smell bad eggs ' stin bombs (2)
an0 two $ar2 first one on eac* line
/uation 2!a% + 22&O4!a2&O4+ 22O + %2+ &O2
to reduction products $rom !a2&O4eg 2& or & or &O2+ %2(s) (1) 4balanced euation (1)
($) Obser"ation (&tarts) blue or blac (1) colourless (1)
/uation %2+ 2!a2&2O32!a% + !a2&4O(1) 3
(or %2+ 2&2O32
2%
+ &4O2
)
[1%]
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14. (a) decreasesB 1
increase in shielding B 1
&or ato$ic radius'
less attraction $or bonding &or s*ared' electronsB 1
(b) bron solutionB 1
&or blac2 solid'
Cl2+ 2/% 2/Cl +%2B 1
&or ionic euation'
(c) &O2B 1
O2&O2e4&O 222
4 ++ +
B 1
& (also 2&)B 1
BO4&e1>&O(orO4&e"&O 222
422
4 +++++ ++
1
(d) Cl2+ 2!aO !aCl + !aOCl + 2OB 1
sodium chlorideB 1
1B 1
sodium chlorate(%) (or bleach etc)B 1
+1B 1[1%]
16. (a) Trend decrease (1) C.E ! "#$%&
/x%lanation number o$ shells increases (or atomic radius increases) (1)
increased nuclear shielding(1)
or less attraction $or bond (pair electrons)
3
1'. (a) (i) 2 O= 2
(ii) !a% or !aAt or %
or iodide or At
or Astatide (1)ot atoms or molecules
(iii) &mell o$ bad eggs (1)
Allow &bAc"goes blac! and '"Cr"(7)*+
goes cloudy green
(i,) " e
+ " ++ 2&O42& + 42O (1)
( 10 *++(%
"-
4
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(b) (i) * or Cl (1)C. / 0 if redo answer gien
If wrong 2alide gien allow ma one in b3iii4
If a5 or aCl, or 5-
or Cl-
gien lose mar! in 3i4
6ar! on if is e8g8 *5"or *"5
(ii) !a* or !aCl or *
or Cl
(1)
(iii) A proton donor or an acid (1)
(i,) ++*
*
( *"(%+ a5 a*(%+ *5
( *"(%+ " a5 a"(%+ " *5
( for c2loride
4
[9]
18. (a) decreases (1)
attraction $or bonding pair goes don (1)
or electron densit0 in bond, or co"alent &or bonding' electrons
as sie o$ atoms or shielding goes up (1) 3
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(b) (i) .r 2 (1)
for$ulae not na$es, gases or fu$es, not solutions
bron $umes (1)
or 0ellow-brown or orange, not 0ellow
%2 (1)
,iolet $umes or blac solid (1)
or %ur%le fu$es
(ii) &O2 (1) & (1) 2& (1)
& and 2& (1)
>enalise $issing ( once onl0
(iii) .r (1) % (1) (not steam)
na$e or for$ula
%enalise wrong state s0$bols once onl0
acidbase or displacement (1) 11[1%]
19. (i) ionisation energ7 decreases don group (1)
radius or shielding increases (1)
electronegati,it7 decreases don group (1)
radius or shielding increases (1)
attraction $or electron pair in co,alent bond decreases (1)
(ii) .eCl2is co,alent (1)
.e(O)2 is amphoteric (1)
dissol,es in e0cess !aO (1)
$orming .e(O)4D2
ions (1)
.e2+
ion has high charge to sie ratio (1)
polarises anions (1)
ma0 1>
[10]
20. (a) (i) !O3or C3COO(1)
C. in 3a4 if incorrect acid gien
(ii) 2!O3+ !a2CO32!a!O3+ CO2+2O (1) 2
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(b) (i) %
or At
not elements9 atoms or molecules(1)
(ii) *
not elements9 atoms or molecules (1) 2
(c) (i) Cl
(1)Allow AgCl ot element, atoms or molecules
(ii) .r
(1)Allow Ag:r ot element, atoms or molecules
2[;]
21. (a) Chlorine added to bromide
;ello'orange solution (or colour) but not precipitate or gas$ormed (1)
Allow:? orange or 0ellow?brown @ 0ellow?red@ orange?brown@
orange?red but NOT red or brown
2.r
+ Cl22Cl
+ .r2 (1)
Allow $olecular euations@ allow euations wit* 39r@
ignore state s0$bols
C$#%* +* -$ $*
.ron solution (or colour) or blac or gre7 or purple'blac
precipitate (1)
#o not allow %ur%le solution or %ur%le fu$es or brown %reci%itate
2%
+ Cl22Cl
+ %2(1) 4
Allow $olecular euations@ allow euations wit* 3I@ ignore state s0$bols
(b) C$%*%-#+-* /# + +* -$ + #$*
If aueous sul%*uric acid used, or 4onc H(O&a', in an0
section, do not allow $ar2s for obser"ations in t*at section.
Orange or bron or 7ello or 7ello-red (or these colours-combined)
$umes'gas(1)
#o not allow red on its own
&team7 or hite $umes or mist7 (1)
&tated reduction productB- &O2&wrong if extra %roduct&s' gi"en'
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C$%*%-#+-* /# + +* -$ +% $*
8urple $ume or blac solid (1)
&team7 or hite $umes or mist7 (1)
;ello (solid) (1)
&mell o$ bad eggs (1)
&tated reduction productsB- &O29 &9 2& &all t*ree $ust be gi"en' (1)
#o not extract t*ese %roducts fro$ euations@ wrong if extra
%roduct&s' gi"en
+!*+-$%/
Ignore state s0$bols in euations
2.r
.r2 + 2e
(1)
4++ &O42+ 2e&O2 + 22O (1)
or 2++ 2&O4+2e
&O2 + 22O
O,erall e:uation
4++ &O4
2+2.r
&O2 + 22O + .r2 (1)
or 2++ 2&O4 + 2.r
&O2 + 22O + .r2 E
[1#]
24. Addition o$ sil,er nitrate !o precipitate ith $luoride ions (1)
hite precipitate ith chloride ions (1)
Cream precipitate ith bromides ions (1)
;ello precipitate ith iodide ions (1)
Addition o$ ammonia solution AgCl precipitate dissol,es in dilute !3 (a:) (1)
Ag.r precipitate sparingl7 soluble in dilute !3 (a:)
O= soluble in concentrated !3 (a:) (1)
Ag# precipitate insoluble in concentrated
!3 (a:) (1) G2(1) 1
(b) Obser,ation ith a:ueous /C1 ;ello solution or no reaction (1)
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Obser,ation ith a:ueous /% .ron solution or blac precipitate (1)
%onic e:uation 2%
+ .r2 2.r
+ %2(1) 3
(c) (i) Cl2(1)
(ii) 2O + Cl2 Cl + ClO (1)
(iii) =ed colour due to presence o$ acid or +ions (1)
hite due to bleading b7 ClO (1) 4
(d) 2!aO + Cl2 !aCl + !aClO + 2O (1) 1
[
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26. (a) (i) AH calcium iodide ' Ca%2 ' an7 calcium (1)
7H sil,er iodide ' Ag% onl7 (1)
CH iodine ' %2 onl7 (1)
DH sodium thiosulphate ' !a2&
2O
3onl7 (1) 4
(ii) 2Ag!O3 + Ca%2 2Ag% + Ca(!O3)2
$# Ag+
+ %
Ag% (1) 1
allo e:uation conse:uential on identit7 o$ Ain (i)
allo an7 Ca'&r'#i halide
(b) (i) to $actors h7dration energ7 ' e0planations in terms o$ h7dration (1)
lattice energ7 ' e0planations in terms o$
breaing don lattice (1)
e0planation h7dration energ7 o$ .a2+
is smaller than 6g2+
'
insu$$icient h7dration energ7 to o,ercome lattice
energ7 $or .a&O4(1)
3
(ii) .a2+
(a:) + &O42
(a:) I .a&O4(s)
$or ionic e:uation (1)
$or state s7mbols (ma7 be aarded $rom a molecular e:uation) (1) 2
(c) (i) !aCl + 2&O4 Cl + !a&O4(1) 1
allo !a2&O4ith correct balancing
(ii) compound &O2onl7 (1)
o0idation state +4 (1)
2
must ha,e + sign be$ore or =oman numeral
allo this mar mar conse:uentiall7 on 2&9 2&O39 but not &9 &O3
(iii) 2.r + 2&O4 .r2 + &O2 + 22O
all $ormulae correct (1)
correctl7 balanced (1) 2
allo 2&O3
(i,) an7 bron ' orange ' red ' steam7 $umes ' hite $umes '
choing smell '$roth (1) 1
[1;]
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2'. (a) a substance hich accepts electrons ' remo,es electrons
($rom another substance) (1)
%$-Just remo,al o$ electrons 1
(b) decreasing trend in o0idising poer (1)
halogen atoms become larger ' ha,e more shells ' more shielding (1)less attraction $or electrons %$- loer electronegati,it7 (1)
allo re,erse argument $or %* 3
(c) (i) /%(a:) colourless +% Cl2(a:) colourless'green ' 7ello
green ' 7ello(1)
7ello ' orange ' bron (solution) ' blac (precipitate) (1)
%$- clear9 %$-purple
i$ 7ello gi,en $or Cl2(a:)9 must be darer colour $or mi0ture 2
(ii) 2/% + Cl22/Cl + %2
$# /% + K Cl2/Cl + K%2
$# %
K Cl2 Cl
+ K %2
$# 2%
+ Cl22Cl
+ %2 (1)
%$- an e:uation ith ClO
1
(iii) iodide ' %
' /% ' potassium iodide (1) 1
(i,) KCl2+ e
Cl
$# Cl2+ 2e
2Cl
(1)
%
K %2+ e
$# 2%
%2 2e
(1)
allo 1 mar $or o0idising and reducing in rong spaces 2
(d) (i) o0idation number o$ iodine in %O3
H ' +5 (1)
o0idation number o$ iodine in %H 1 (1)
o0idation number o$ iodine in %2H > (1)
penalise 5+ and 1 onceB penalise tice i$ 5 and 1 gi,en 3
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(ii) %O3
+ 5%
+ +3%2+ 32O
all species present (ignore electrons) (1)
balanced (1)
allo /%O3%O3
and /% %2$or species mar
i$ / included9 /+must appear on rhs $or balanced mar
similarl7 $or 2&O4' Cl instead o$ +
2
[1$]
28. (a) %ncrease in boiling temperature
6olecular sie increases $rom *2to %2 (1)
,an der aals attracti,e $orces increase (1) 2
(b) =educing poer increases $rom *
to At
(1)
%onic sie increase (1)
Outer electrons $urther $rom the nucleus'more shielded (1)
#ess strongl7 attracted' more easil7 lost (1) 4
(c) At (g) (1)
Astatide a base'proton acceptor (1)
!aAt + 2&O4!a&O4+ At (1)
&O2(g) (1)
Astatide a reducing agent (1)
2At
At2+ 2e
(1)
2&O4+ 2++ 2e
&O2+ 22O (1)
or 2!aAt + 22&O4&O2+ At2+ 22O + !a2&O4 (2)
2&(g) (1)
Astatide a reducing agent (1)
"At
4At2+ "e
(1)
or 2&O4+ "++ "e
2& + 42O (1)
"!aAt + 52&O42& + 4At2+ 42O + 4!a2&O4 2D 6a0 E
[1$]
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29. (a) Lecreases (1)
Atomic radius ' sie increase or atom has more shells more shielding
or more shells (i$ not gi,en abo,e) (1)
less attraction $or shared electron pair or electrons ' electron
densit7 ' electron pair in a co,alent bond (1) 4If wrong trend gien allow ma ["] for At8 ad8 increases314 s2ells)s2ielding increases
(b) %ncreases (1)
6olecular sie increases ' molicules ha,e more electrons ' molecules
ha,e more shells ' larger molecular mass (1)
%ncrease in intermolecular $orces ' ,an der aal $orces ' ,d
e0plained (1)6ar! C. if trend incorrect8 6ar! eplanation points separately
ote= In part 3a4 mar! C. if ions or molecules discussedA5>. a correct trend mar! awarded8
3[7]
30. (a) (i) abilit7 o$ an atom to ithdra electrons (1)
$rom a co,alent bond (1)
(ii) attraction $or electron pair goes don
as sie o$ atoms or shielding goes up (1) 3
(b) /ffect on bond %olarit0 !one (1)
/x%lanation e:ual and opposite e$$ect
$rom each atom cancels out (1)
2
(c) (i) &O2(1)
&O2(1)2& (1)
(ii) .r 2(1) bron $umes (1)
%2 ,iolet'purple $umes (1)
.r and % (1) steam7 $umes (1)
E[1%]
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31. (a) (i) &O2(1)
(ii) 2& (1) 2
(b) (i) l K l2+
+
+ e
(1)
(ii) "++ 2&O4+ "e
2& + 42O (1)
(iii) 2++ 2&O4+ 2e
&O2 +22O (1)
(i,) lO% + 22&O42& + &O2+ 5%2+ 2O
components (1) balance (1)
5
(c) /uation 2O
+ Cl2OCl
+ Cl
+ 2O (1)
4o$$ercial use OCl
is a bleach'disin$ectant (1)
2[
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(ii) mol thio H 23> N 1>3
N >1>> (1)H 23 N 1>3
mol %2 H mol thio'2 (1)
H 115 N 1>3
(1)
mol ClO
in 25 cm3
diluted solution H mol %2(1)
H 115 N 1>3(1)
mol ClO
in 25>cm3diluted solution H 1> N 115 N 1>
3(1)
H 115 N 1>2
(1)
mol ClO
in original 1> cm3
solution H 115 N 1>2
(1)
6ultipl7 b7 1>> to con,ert 1> cm3
to 1> dm3
(1)
ence mol dm3
H 1>> N 115 N 1>2
H 115 (1)
13
6ass %
H mole Ag% NArH 24 N 1>3
N 12< (1) H >3>5g
ence mass Ag.r H >E>2 >54 H >33"g (1)
6oles Ag.r H mass'5rH >33"'1"" (1) H 1" N 1>3
6ass .rH 6ole 0ArH 1" N 1>3N "> (1) H >144g
8ercentage .r
in sample H >144 N 1>>'>545 H 24 (2 23>5 N 1>>'>545 H 55E (5 >5) (1)
E+-$% +#/
Ag+ + %
Ag% (1)
Ag+ + .r
Ag.r (1)
Ag.r + 2!3Ag(!3)2D++ .r
(1)
[6a 1$]
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3'. (a) A reagent hich taes or accepts electrons (1) 1
(b) 6n has been reduced $rom %% to % (1)
6n has been reduced $rom %% to % (1)
O07gen has been o0idised $rom 2 to ero (1) 3
(c) (i) Cl2+ 2O 2++ ClO
+ Cl
(1)
(ii) O
remo,es + (1)displacing e:uilibrium to the right (1)
++ O
2O (1)
or C12 + 2!aO !aClO + !aCl + 2O 4
[9]
38.
(b) Addition o$ sil,er nitrate
Chloride gi,es hite precipitate ' solid (1)
.romide gi,es cream precipitate ' solid (1)
%odide gi,es 7ello precipitate ' solid (1)
Addition o$ ammonia
Chloride precipitate soluble in dilute (1)
.romide precipitate soluble in concentrated (1)
%odide precipitate insoluble (1)?o not allow 2alogen or sodium 2alide
[1$]
40. (i) 7dro0ide solubilit7 increases
&need trend'
1
&ulphate solubilit7 decreases
&need trend'
1
&If bot* 5g
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(ii) &acce%t HNO
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42. (a) %ncreases
1
eat or steam or gas phase or temp (P1>>Q) &NOT *ot'
1
6g + 2O 6gO + 2
1&Ignore state s0$bols - e"en if t*e0 are wrong'
(b) hite precipitate'solid'suspension (!ot Rcloud7 ' mil7)
1
.eCl2+ 2!aO .e(O)2+ 2!aCl
Or .e2+
+ 2O
.e(O)21
&Acce%t 9e4l+ OH-
9e&OH'+ 4l-'
8pt (re)dissol,es or solution goes clear 1
&Allow %%t disa%%ears'
&NOT solution for$s'
.e(O)2+ 2O
2
4.e(O)
BNOT4
+.e(O) C
Or .e(O)2+ 2!aO !a2.e(O)4 1
[7]
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44. (a) .arium dissol,es (1) (or $orms solution
as e,ol,ed (1) (or h7drogen e,ol,ed) or
bubbles gets hot (1)do not allow eolution of wrong gas
.a(s) + 22O(l) .a
2+(a:) + 2O
(a:) (or .a(O)
2(a:) +
2(g)
&pecies all correct (1)
&tate s7mbols correct (1) (pro,ided species are correct)
.alanced e:uation (1)
hite precipitate ith sodium sulphate (1)
(or hite solid or suspension or hite cloud7 or mil7)
.a2+
(a:) + &O42
(a:) .a&O4(s)
(or .a(O)2(a:) + !a2&O4(a:) .a&O4(s) + 2!aO(a:)
&tate s7mbols (1)
.alanced e:uation (1)3mar! obs8 of ppts independently 3and in 3b44
"
(b) ith .eCl2and !aO get a hite precipitate (1) (or solid etc)
because .e(O)2is insoluble (1) (or hite ppt is .e(O)2)
ppt is soluble in e0cess reagent (1)
.ecause .e(O)2is amphoteric (or ber7llium $orms comple0 ion
(.e(O)4)2
) (1)
&T*is is t*e ualit0 of language $ar2 so t*e ter$s $ust be used in
a sentence'
ith 6gCl2get hite ppt (1).ecause 6g(O)2is sparingl7 soluble (or insoluble) (1)(or hite ppt is
6g(O)2)
ith .aCl2no ppt $ormed (1)(or no reaction) (or remains in solution)
.ecause .a(O)2is soluble (1) (or all species are soluble)
&olubilit7 o$ h7dro0ides increases don roup (1)ote can ta!e mar!s for :e3(*4"3s4, 6g3(*4"3s4, :a3(*4"3aq4
from equations@rong formula for 63(*4"loses mar!
ma0 "
(c) (i) O H 55
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(ii) $ormulaempirical
$ormulamolecular
H an integer (1) ($# + %*#)Allow correct definitions as an alternatie for t2e mar!emp8 form8 >2e simplest ratio of atoms of eac2 element in acompound molec8 form8 >2e actual number of atoms ofeac2 element in a molecule
6r (1)(or molar mass or =*6 !O? molecular mass) 5["1]
45.
(a) (i) an7 to o$
e$$er,escence ' $iing ' bubbling ' hite precipitate or sediment '
solution gets arm ' metal dissol,es or disappears (2) 2
(ii) comparisons needed $or the to obser,ations gi,en in (a) (i)
more (rapid) e$$er,escence: more ,igorous reaction 'less or no (hite) precipitate ' solution gets hot ie hotter than in (i) '
metal dissol,es more :uicl7 (2) 2
(iii)Ca + 22O Ca(O)2+ 2 (1) 1
(b) (i) starch (1) 1
(ii) hen the solution is coloured (pale) 7ello ' stra ' close to the end point
independent o$ (c)(i) 1
(iii) blue ' blac9 allo purple9 ignore bron (1)
to colourless %$-clear (1)
allo 1 mar i$ re,ersed 2
(i,) ClO (+)1 Cl 1 condone ClO 1+ and Cl 1D (1)
1
(,) %
1 %2 > condone 1- $or %-D (1)
1
(,i)
ClO+ 2++ 2% Cl+ %2+ 2O
(1) 1%$-/%
allo spectator /+ions i$ on both sides
[1"]
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46. 6.L. 7 ualit0 of language $ar2s
(a) A%
(high) melting point immediate beteen &i S 8 (1)
metallic bonding (1)
6.L
delocalised electrons mentioned in a sentence e0plaining metallic bonding (1)
energ7 re:uired to brea bonds (1)ote= last mar! note scored if t2ere is a contradiction e8g ionic bonding ormolecules or 8d8w8 forces
S$%
highest melting point (1)
co,alent (1)macromolecular (1)(or giant structure)
much energ7 needed to brea bonds (1)(or di$$icult to brea bonds)
;$/$#/
loest melting point (1)
molecular (1)(or 84)
, d $orces beteen molecules (1)
easil7 broen (1)(or not much energ7 re:uired to brea bonds) 12
(b) Al good conductor (1)
delocalised electrons (1)(or Rsea o$ or R$ree electrons)
&i9 84non-conductors (1)(ie &i and or 8B i$ one rong loses mar)
Mlectrons localised (1)(or no $ree electrons or no $ree charged particles)3can score for i or for &4
4
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(c) 6g reacts ith steam (1)(or ater ,apour)
6g+2O6gO+2(1)
3can score t2is mar! if water not steam gien4
hite solid (1)(or 6g glos)
3can only score if steam gien4
Ca reacts ith (cold) ater $aster than 6g (1)
Ca+22OCa(O)2+2(1)
gas bubbles (1)(or $i) !O? h7drogen produced
8roduct dissol,es (or $orms a (hite or ppt or cloud7) solid) (1)
(or Ca dissol,es)