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Unit 4 January 04 Markscheme

Q1

(a) (i) 4Al + 3O2 2Al2O3(1)

Ignore state symbols

Ionic/ electrovalent/ ionic with covalent character(1) 2

(ii) S + O2 SO2(1)

Allow equations based on S2 or S8Covalent(1) 2

(b) (i) Amphoteric / acid and base (1)

H+

in one equation, OH-in another(1)

ORMolecular equations using HCl and NaOH (1 max)

Al2O3 + 3H2O + 2OH

2Al(OH)4

OR............. + 6OH

2Al(OH)63

OR equation with AlO2

as product (1)

A12O3 + 6H+ 2Al

3++ 3H2O (1)

State symbols not required

Equations using Al(OH)3 (1 max) 4

(ii) Acidic (1)

SO2 + 2OH SO32+ H2O

OR SO2 + OH

HSO3

OR any correctly balanced equation with SO2 and H2O as reactants

and appropriate combinations of SO32

, HSO3

; H+

and

H3O+

as products (1) 2

(c) (i) PCl3 + 3H2O 3HCl + H3PO3(2)

Species (1), balancing (1), allow P(OH)3 as product 2

(ii) A pair of electrons/ lone pair from the oxygen in a water molecule

(1)

cannot form a bond with/ donate electrons to the carbon atom (1)because the C atom has no available orbital / no 2d / carbon is a

small atom surrounded by chlorine atoms /chlorine atoms are large

and surround the carbon atom (so the attack is sterically hindered)

sense of relative size needed, steric hindrance is not enough (1)

Therefore a CCl bond has to be broken (first), which is strong /

Ea too high (1) 4

(d) Reaction II as the lead +2 state is more stable than the lead +4

OR vice versa in terms of tin

OR +2 oxidation state becomes more stable down the group (1)

PbCl4 / Pb 4+ is oxidising but SnCl4 / Sn 4+ is not (1)

For this mark a reference to the relative oxidising power of PbCl4 and

SnCl4 is needed 2

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[18]

Q2

(a) (i) Propanoyl chloride 1

(ii) Ammonia (1)Phosphorus pentoxide/ phosphorus(V) oxide/ P2O5 / P4O10(1)

Name or formulae acceptable, but if both given, both must be

correct 2

(iii) Bromine (1)NOTaq/gas

(conc) aq NaOH / KOH (1)

Heat (under reflux) (1) This mark is conditional on both reagents

being stated 3

(b) (i) (Substance) AOR correct name (1)

C2H5COCl + H2O / C2H5COOH + HCl (1) 2

(ii) (Substance) ZOR correct name (1)

C2H5NH2 + H2O / C2H5NH3+

+ OH

(allow C2H5NH3OH)

(1)

Each equation can score 2 marks if no substances are stated. 2[10]

Q3

(a) Restricted rotation / lack of free rotation around C=C (1)

NOTcannot rotate

There are two different groups on each carbon of C=C / four different

groups around two carbon atoms (1) 2

(b) Potassium dichromate (1)

If given oxidation state must be correct

dilute H2SO4 / H2SO4 solution (1)

(Heat and) distil off (citral as it is formed) (1)

IF KMnO42 maxie 2nd

and 3rd

marks 3

(c) (i) Brown / orange / yellow colourless / decolourises / disappears 1

(ii) Yellow/ orange/ red precipitate / crystals / solid 1

(iii) Red precipitate / crystals/ solid 1

(d) (i) C6H11(CH3)(Br)CCH2CHO OR C6H11(CH3)HCCH(Br)CHO

brackets essential

C H C C C H O C H C C C H O1 1 1 1

3 3

6 6

B r B rH H

H HH C H CO R

1

(ii) C6H11(CH3)C=CHCH(OH)CN brackets essential

OR

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C HC C

C

1 1

3

6

H

O H

HC H

C N

NOT with bond going to N 1

(iii) C6H11(CH3)C=CHCH(OH)CH3brackets essential

OR

C HC C

C

1 1

3

3

6

H

O H

HC H

C H

ALLOW mixture of displayed and structural formulae in (i), (ii) and

(iii) 1

[11]

Q4

(a) (i) The heat (energy) / enthalpy change when 1 mol of gaseous atoms

(1)

NOTenergy on its own

is formed from the element (1) 2

(ii) Cl2

(g) Cl (g) 1

(iii)

S r ( g ) 2 C l ( g )

2 C l ( g )

S r ( g )

S r ( g )

S r ( s ) + C l ( g ) S r C l ( s )2 2

+

2 +

H f

Cycle marks:

1 markfor cycle showing all balanced species

1 markfor all state symbols correct

Allow Sr(g) Sr2+

(g) as a single stage

Calculation marks:

Hf= sum of other terms and / or

829 = +164 +550 +1064 + 2 x ( +122) + 2 x ( 349) + LE

or LE= 82916455010642 x(+122) 2x(349) 2

ie 1 markfor multiplyingHa of Cl by 2

1 markfor multiplying EA of Cl(g) by 2

LE = 2153 (kJ mol1

) (1)

The answer markisconsequential on whether they multiply neither

or

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just one ofHa and EA by 2 , butnotconsequential if they have

wrong

signs. 5

(b) (i) + 737 = HfSrCl + 122 ( 829) OR correct cycle (1)

HfSrCl = 214 (kJ mol

1

) (1) 2(ii) As the reaction (left to right) is endothermic (1)

a decrease in temperature will decrease the value ofK(1)

thus the equilibrium position will shift to the left (1) 3

(iii) Kp= psrCl pCI(1)MUST be stated

moles of SrCl = moles of Cl (1) This can be stated or implied

pSrCl = pCl = 4.2 = 2.1 (atm) (1)

Kp = 2.1 atm 2.1 atm = 4.4(l) (1) atm2(1)

Units are NOT consequential on wrong Kp 5

[18]

Q5

(a) (i) NH3 base and NH4+

acid (1)

H2O acid and OH

base (1)

OR

linking(1)

acid and base correctly identified(1) 2

(ii) Starting pH of (just above) 11 (1)

Graph showing vertical line between pH 4 and 6With vertical section 35 units in length (1)

at a volume of HCl of 20 cm3(1)

Final pH of between 1 and 2 (1) 4

(iii) Named indicator consequential on vertical part of their graph (1)

Because all of its range is within the vertical part of the graph /

pKind 1 is within vertical part of graph / it changes colour

completely/ stated colour change (MO: yellow red; BB: blue

yellow; PP: pink colourless) within the pH of the vertical part of

the graph (1) 2

(b) (i) Ka= [ ] [ ][ ]223

HNONOOH

+

square brackets essential 1

(ii) [H+] = [NO2

] or [H

+]2= Ka [HNO2] (1)

[H+] = (Ka 0.12) = 0.00751 mol dm

3(1)

pH = log [H+] = 2.12/2.1 (1)

ALLOW any correct conversion of [H+l into pH provided the

answer is less than 7 3

(iii) Moles NaNO2 = 1.38/69 = 0.020 (1)

[NO2] = 0.020 / 0.10 = 0.20 (mol dm3)

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[H+] =

salt][

acid][a

K

=20.0

120.01070.4 4 = 2.82 10

4(1)

pH = log 2.82 104

= 3.55 /3.6 /3.5 (1) 4

(iv) In a buffer both [acid] and [salt] must be large compared to the

added H+

or OH-

ions (1)but in NaNO2 alone [ HNO2] is very small (1)

OR

to remove both H+

and OH

there must be a large reservoir of

both NO2

ions and HNO2 molecules (1)

which there are a solution of NaNO2 and HNO2 but not in NaNO

alone (1) 2[18]