redox trends-qa mark scheme

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)


13/29

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

[


14/29

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%]


18/29

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[


19/29

(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$]


23/29

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


25/29

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]


26/29

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


27/29

(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"]


28/29

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


29/29

(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)

redox trends-qa mark scheme

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