2.

1 [131 marks]
1. [1 mark]
What is the relative atomic mass, Ar , of an element with this mass spectrum?

A.  24.0

B.  24.3

C.  24.9

D.  25.0

Markscheme
B
2a. [1 mark]
Chlorine undergoes many reactions.
State the full electron configuration of the chlorine atom.
Markscheme
1 s 2 2 s 2 2 p6 3 s 2 3 p5 ✔
Do not accept condensed electron configuration.
2b. [1 mark]
State, giving a reason, whether the chlorine atom or the chloride ion has a larger radius.

Markscheme
C l − AND more «electron–electron» repulsion ✔

Accept C l − AND has an extra electron.

2c. [2 marks]
Outline why the chlorine atom has a smaller atomic radius than the sulfur atom.

Markscheme
C l has a greater nuclear charge/number of protons/ Z ef f «causing a stronger pull on the
outer electrons» ✔
same number of shells
OR
same «outer» energy level
OR
similar shielding ✔
2d. [1 mark]
The mass spectrum of chlorine is shown.
NIST Mass Spectrometry Data Center Collection © 2014 copyright by the U.S. Secretary of
Commerce on behalf of the United States of America. All rights reserved.

Outline the reason for the two peaks at m/ z=35 and 37.

Markscheme
«two major» isotopes «of atomic mass 35 and 37» ✔
2e. [2 marks]
Explain the presence and relative abundance of the peak at m/ z=74.
Markscheme
«diatomic» molecule composed of «two» chlorine-37 atoms ✔
chlorine-37 is the least abundant «isotope»
OR
low probability of two Cl37 «isotopes» occurring in a molecule ✔
2f. [1 mark]
2.67 g of manganese(IV) oxide was added to 200.0 c m3 of 2.00 m o ld m −3 H C l .
M n O2 ( s )+ 4 H C l ( a q ) →C l 2 ( g ) +2 H 2 O ( l )+ M n C l 2 ( a q )

Calculate the amount, in m o l, of manganese(IV) oxide added.

Markscheme
2.67 g
¿< =¿>0.0307< ¿ mo l>¿ ✔
86.94 g m o l −1
2g. [2 marks]
Determine the limiting reactant, showing your calculations.
Markscheme
¿< nH C l=2.00 m o l d m−3 ×0.2000 d m3 >¿=0.400 mo l✔
0.400
¿< =¿> 0.100 mo l  AND  M nO2  is the limiting reactant ✔
4
Accept other valid methods of determining the limiting reactant in M2.
2h. [1 mark]
Determine the excess amount, in m o l, of the other reactant.

Markscheme
¿< 0.0307 mo l ×4=0.123 mo l>¿
¿< 0.400m o l 0.123 mo l=¿ >0.277<¿ m o l>¿ ✔
2i. [1 mark]
Calculate the volume of chlorine, in d m3, produced if the reaction is conducted at standard
temperature and pressure (STP). Use section 2 of the data booklet.

Markscheme
¿< 0.0307 mo l ×22.7 d m 3 m o l −1=¿> 0.697<¿ d m 3> ¿ ✔

Accept methods employing p V =n R T .

2j. [2 marks]
State the oxidation state of manganese in M nO2  and M nC l 2.
Markscheme
M nO 2 :+ 4 ✔

M nC l 2 :+2 ✔

2k. [1 mark]
Deduce, referring to oxidation states, whether M nO2 is an oxidizing or reducing agent.

Markscheme
oxidizing agent AND oxidation state of M n changes from + 4 to +2/decreases ✔
2l. [1 mark]
Chlorine gas reacts with water to produce hypochlorous acid and hydrochloric acid.
C l 2 ( g )+ H 2 O ( l ) ⇌ H C l O ( a q ) + H C l ( a q )

Hypochlorous acid is considered a weak acid. Outline what is meant by the term weak acid.
 

Markscheme
partially dissociates/ionizes «in water» ✔
2m. [1 mark]
State the formula of the conjugate base of hypochlorous acid.

Markscheme
C l O − ✔
2n. [1 mark]
Calculate the concentration of H +¿ ( a q) ¿ in a H C lO ( a q ) solution with a p H=3.61.

Markscheme
¿<¿ ✔
2o. [1 mark]
State the type of reaction occurring when ethane reacts with chlorine to produce
chloroethane.

Markscheme
«free radical» substitution/ S R ✔

Do not accept electrophilic or nucleophilic substitution.

2p. [1 mark]
Predict, giving a reason, whether ethane or chloroethane is more reactive.

Markscheme
chloroethane AND C C l bond is weaker/324 k J m o l −1 than C H bond/414 k J mo l −1
OR
chloroethane AND contains a polar bond ✔

Accept “chloroethane AND polar”.

2q. [1 mark]
Write the equation for the reaction of chloroethane with a dilute aqueous solution of
sodium hydroxide.

Markscheme
C H 3 C H 2 C l ( l )+ O H − ( a q ) →C H 3 C H 2 O H ( a q )+C l− ( a q )
OR
C H 3 C H 2 C l ( l )+ N aO H ( a q ) →C H 3 C H 2 O H ( a q ) + N aC l ( a q )  ✔

Accept use of  C 2 H 5 C l and  C 2 H 5 O H /C 2 H 6 O in the equation.

2r. [1 mark]
Deduce the nucleophile for the reaction in d(iii).
Markscheme
hydroxide «ion»/O H − ✔

Do not accept N a O H .
2s. [1 mark]
Ethoxyethane (diethyl ether) can be used as a solvent for this conversion. Draw the
structural formula of ethoxyethane

Markscheme

C H3 C H2O C H2 C H3

 /  ✔

Accept ( C H 3 C H 2 )2 O.

2t. [2 marks]
Deduce the number of signals and their chemical shifts in the H1 NMR spectrum of
ethoxyethane. Use section 27 of the data booklet.
Markscheme
2 «signals» ✔
0.91 .0<¿ p p m>¿ AND 3.33 .7<¿ p p m>¿✔

Accept any values in the ranges.

Award [1 max] for two incorrect chemical shifts.
2u. [2 marks]
C C l 2 F2 is a common chlorofluorocarbon, C F C.

Calculate the percentage by mass of chlorine in C C l 2 F2.

Markscheme
¿< M ( C C l 2 F2 ) =¿>120.91<¿ g mo l − 1>¿ ✔

2× 35.45 g m o l −1
×100 %=¿ >58.64<¿ % >¿ ✔
120.91 g m o l −1

Award [2] for correct final answer.

2v. [1 mark]
Comment on how international cooperation has contributed to the lowering of C F C
emissions responsible for ozone depletion.
Markscheme
Any of:
research «collaboration» for alternative technologies «to replace C F Cs»
OR
technologies «developed»/data could be shared
OR
political pressure/Montreal Protocol/governments passing legislations ✔
 
Do not accept just “collaboration”.
Do not accept any reference to C F C as greenhouse gas or product of fossil fuel combustion.
Accept reference to specific measures, such as agreement on banning use/manufacture of
C F Cs.
3a. [1 mark]
State the full electron configuration of the chlorine atom.

Markscheme
1 s 2 2 s 2 2 p6 3 s 2 3 p5 ✔

Do not accept condensed electron configuration.

3b. [1 mark]
State, giving a reason, whether the chlorine atom or the chloride ion has a larger radius.
Markscheme
C l − AND more «electron–electron» repulsion ✔

Accept C l − AND has an extra electron.

3c. [2 marks]
Outline why the chlorine atom has a smaller atomic radius than the sulfur atom.

Markscheme
C l has a greater nuclear charge/number of protons/ Z ef f «causing a stronger pull on the
outer electrons» ✔
same number of shells
OR
same «outer» energy level
OR
similar shielding ✔
3d. [1 mark]
The mass spectrum of chlorine is shown.
NIST Mass Spectrometry Data Center Collection © 2014 copyright by the U.S. Secretary of
Commerce on behalf of the United States of America. All rights reserved.

Outline the reason for the two peaks at m/ z=35 and 37.

Markscheme
«two major» isotopes «of atomic mass 35 and 37» ✔
3e. [2 marks]
Explain the presence and relative abundance of the peak at m/ z=74.
Markscheme
«diatomic» molecule composed of «two» chlorine-37 atoms ✔
chlorine-37 is the least abundant «isotope»
OR
low probability of two Cl37 «isotopes» occurring in a molecule ✔
3f. [1 mark]
Calculate the amount, in m o l, of manganese(IV) oxide added.

Markscheme
2.67 g
¿< =¿>0.0307< ¿ mo l>¿ ✔
86.94 g m o l −1
3g. [2 marks]
Determine the limiting reactant, showing your calculations.
Markscheme
¿< nH C l=2.00 m o l d m−3 ×0.2000 d m3 >¿=0.400 mo l✔
0.400
¿< =¿> 0.100 mo l  AND  M nO2  is the limiting reactant ✔
4

Accept other valid methods of determining the limiting reactant in M2.

3h. [1 mark]
Determine the excess amount, in m o l, of the other reactant.

Markscheme
¿< 0.0307 mo l ×4=0.123 mo l>¿
¿< 0.400m o l 0.123 mo l=¿ >0.277<¿ m o l>¿ ✔
3i. [1 mark]
Calculate the volume of chlorine, in d m3, produced if the reaction is conducted at standard
temperature and pressure (STP). Use section 2 of the data booklet.
Markscheme
¿< 0.0307 mo l ×22.7 d m3 m o l −1=¿> 0.697<¿ d m3> ¿ ✔

Accept methods employing p V =n R T .

3j. [2 marks]
State the oxidation state of manganese in M nO2  and M nC l 2.

Markscheme
M nO 2 :+ 4 ✔

M nC l 2 :+2 ✔

3k. [1 mark]
Deduce, referring to oxidation states, whether M nO2 is an oxidizing or reducing agent.

Markscheme
oxidizing agent AND oxidation state of M n changes from + 4 to +2/decreases ✔
3l. [1 mark]
Hypochlorous acid is considered a weak acid. Outline what is meant by the term weak acid.
 
Markscheme
partially dissociates/ionizes «in water» ✔
3m. [1 mark]
State the formula of the conjugate base of hypochlorous acid.

Markscheme
C l O − ✔
3n. [1 mark]
Calculate the concentration of H +¿ ( a q) ¿ in a H C lO ( a q ) solution with a p H=3.61.

Markscheme
¿<¿ ✔
3o. [1 mark]
State the type of reaction occurring when ethane reacts with chlorine to produce
chloroethane.
Markscheme
«free radical» substitution/ S R ✔

Do not accept electrophilic or nucleophilic substitution.

3p. [1 mark]
Predict, giving a reason, whether ethane or chloroethane is more reactive.

Markscheme
chloroethane AND C–Cl bond is weaker/324 k J m o l −1 than C–H bond/414 k J mo l −1
OR
chloroethane AND contains a polar bond ✔

Accept “chloroethane AND polar”.

3q. [3 marks]
Explain the mechanism of the reaction between chloroethane and aqueous sodium
hydroxide, N a O H ( a q ), using curly arrows to represent the movement of electron pairs.
Markscheme

curly arrow going from lone pair/negative charge on O in −OH to C ✔

curly arrow showing C l leaving ✔
representation of transition state showing negative charge, square brackets and partial
bonds ✔
 
Accept O H − with or without the lone pair.

Do not accept curly arrows originating on H in O H −.

Accept curly arrows in the transition state.
Do not penalize if H O and C l are not at 180°.
Do not award M3 if O H − C bond is represented. 
3r. [1 mark]
Ethoxyethane (diethyl ether) can be used as a solvent for this conversion.
Draw the structural formula of ethoxyethane
Markscheme

C H3 C H2O C H2 C H3

 /  ✔

Accept ( C H 3 C H 2 )2 O.

3s. [3 marks]
Deduce the number of signals and chemical shifts with splitting patterns in the 1H
NMR spectrum of ethoxyethane. Use section 27 of the data booklet.

Markscheme
2 «signals» ✔
0.9−1.0 AND triplet ✔
3.3−3.7 AND quartet ✔
Accept any values in the ranges.
Award [1] for two correct chemical shifts or two correct splitting patterns.
3t. [2 marks]
Calculate the percentage by mass of chlorine in C C l 2 F2.

Markscheme
¿< M ( C C l 2 F2 ) =¿>120.91<¿ g mo l − 1>¿ ✔

2× 35.45 g m o l −1
×100 %=¿ >58.64<¿ % >¿ ✔
120.91 g m o l −1

Award [2] for correct final answer.

3u. [1 mark]
Comment on how international cooperation has contributed to the lowering of C F C
emissions responsible for ozone depletion.

Markscheme
Any of:
research «collaboration» for alternative technologies «to replace C F Cs»
OR
technologies «developed»/data could be shared
OR
political pressure/Montreal Protocol/governments passing legislations ✔
 
Do not accept just “collaboration”.
Do not accept any reference to C F C as greenhouse gas or product of fossil fuel combustion.
Accept reference to specific measures, such as agreement on banning use/manufacture of
C F Cs.
3v. [2 marks]
C F Cs produce chlorine radicals. Write two successive propagation steps to show how
chlorine radicals catalyse the depletion of ozone.

Markscheme
O3+ C l→ O 2+C l O  ✔

C lO+O → O 2+C l
OR
C lO+O 3 →C l+ 2O 2  ✔

Penalize missing/incorrect radical dot (∙) once only.

4. [1 mark]
Which technique is used to detect the isotopes of an element?
A.  Mass spectrometry

B.  Infrared spectroscopy

C.  Titration

D.  Recrystallization

Markscheme
A
5. [1 mark]

What is represented by A in ❑ZA X 2 −?

A. Number of electrons

B. Number of neutrons

C. Number of nucleons

D. Number of protons

Markscheme
C
6. [1 mark]
Bromine consists of two stable isotopes that exist in approximately a 1 : 1 ratio. The
relative atomic mass, Ar, of bromine is 79.90. Which are the stable isotopes of bromine?
A. 79Br and 81Br
B. 80Br and 81Br
C. 78Br and 80Br
D. 79Br and 80Br

Markscheme
A
7. [1 mark]

Which is correct for ❑34 2−

16 S ?
Markscheme
D
8. [1 mark]

Which is correct for ❑34 2−

16 S ?

Markscheme
D
9a. [1 mark]
This question is about iron.

State the nuclear symbol notation, ❑ZA X, for iron-54.

Markscheme
❑54
26 Fe  [✔]

9b. [2 marks]
Mass spectrometry analysis of a sample of iron gave the following results:
Calculate the relative atomic mass, Ar, of this sample of iron to two decimal places.

Markscheme
«Ar =» 54 × 0.0584 + 56 × 0.9168 + 57 × 0.0217 + 58 × 0.0031
OR
«Ar =» 55.9111  [✔]
«Ar =» 55.91 [✔]
Notes:
Award [2] for correct final answer.
Do not accept data booklet value (55.85).
9c. [2 marks]
An iron nail and a copper nail are inserted into a lemon.
Explain why a potential is detected when the nails are connected through a voltmeter.

Markscheme
lemon juice is the electrolyte
OR
lemon juice allows flow of ions
OR
each nail/metal forms a half-cell with the lemon juice  [✔]
Note: Accept “lemon juice acts as a salt bridge”.
Any one of:
iron is higher than copper in the activity series
OR
each half-cell/metal has a different redox/electrode potential  [✔]
Note: Accept “iron is more reactive than copper”.
iron is oxidized
OR
Fe → Fe2+ + 2e–
OR
Fe → Fe3+ + 3e−
OR
iron is anode/negative electrode of cell  [✔]
copper is cathode/positive electrode of cell
OR
reduction occurs at the cathode
OR
2H+ + 2e− → H2  [✔]
electrons flow from iron to copper  [✔]
 
Notes:
Accept “lemon juice acts as a salt bridge”.
Accept “iron is more reactive than copper”.
10a. [1 mark]
Dinitrogen monoxide, N2O, causes depletion of ozone in the stratosphere.
Outline why ozone in the stratosphere is important.

Markscheme
absorbs UV/ultraviolet light «of longer wavelength than absorbed by O2»  [✔]
10b. [1 mark]
Different sources of N2O have different ratios of 14N:15N.
State one analytical technique that could be used to determine the ratio of 14N:15N.

Markscheme
mass spectrometry/MS  [✔]
10c. [2 marks]
A sample of gas was enriched to contain 2 % by mass of 15N with the remainder being 14N.
Calculate the relative molecular mass of the resulting N2O.

Markscheme
(98 ×14 )+(2 ×15)
«  =¿» 14.02  [✔]
100
«Mr = (14.02 × 2) + 16.00 =» 44.04  [✔]
10d. [2 marks]
Predict, giving two reasons, how the first ionization energy of 15N compares with that of
14
N.

Markscheme
Any two:
same AND have same nuclear charge/number of protons/Zeff  [✔]
same AND neutrons do not affect attraction/ionization energy/Z eff
OR
same AND neutrons have no charge [✔]
same AND same attraction for «outer» electrons [✔]
same AND have same electronic configuration/shielding [✔]
 
Note: Accept “almost the same”.
“same” only needs to be stated once.
10e. [1 mark]
Suggest why it is surprising that dinitrogen monoxide dissolves in water to give a neutral
solution.

Markscheme
oxides of nitrogen/non-metals are «usually» acidic  [✔]
11a. [1 mark]
Dinitrogen monoxide, N2O, causes depletion of ozone in the stratosphere.
Outline why ozone in the stratosphere is important.

Markscheme
absorbs UV/ultraviolet light «of longer wavelength than absorbed by O2»     [✔]
11b. [2 marks]
Dinitrogen monoxide in the stratosphere is converted to nitrogen monoxide, NO (g).
Write two equations to show how NO (g) catalyses the decomposition of ozone.
Markscheme
NO (g) + O3 (g) → NO2 (g) + O2 (g)       [✔]
NO2 (g) + O3 (g) → NO (g) + 2O2 (g)     [✔]
 
Note: Ignore radical signs.
Accept equilibrium arrows.
Award [1 max] for NO2 (g) + O (g) → NO (g) + O2 (g).
11c. [1 mark]
Different sources of N2O have different ratios of 14N : 15N.
State one analytical technique that could be used to determine the ratio of 14N : 15N.

Markscheme
mass spectrometry/MS     [✔]
11d. [2 marks]
A sample of gas was enriched to contain 2 % by mass of 15N with the remainder being 14N.
Calculate the relative molecular mass of the resulting N2O.
Markscheme
(98 ×14 )+(2 ×15)
«  =» 14.02    [✔]
100
«Mr = (14.02 × 2) + 16.00 =» 44.04    [✔]
11e. [2 marks]
Predict, giving two reasons, how the first ionization energy of 15N compares with that of
14
N.

Markscheme
Any two:
same AND have same nuclear charge /number of protons/Zeff      [✔]
same AND neutrons do not affect attraction/ionization energy/Z eff
OR
same AND neutrons have no charge       [✔]
same AND same attraction for «outer» electrons     [✔]
same AND have same electronic configuration/shielding     [✔]
 
Note: Accept “almost the same”.
“Same” only needs to be stated once.
11f. [2 marks]
Explain why the first ionization energy of nitrogen is greater than both carbon and oxygen.
Nitrogen and carbon:
Nitrogen and oxygen:

Markscheme
Nitrogen and carbon:
N has greater nuclear charge/«one» more proton «and electrons both lost from singly filled
p-orbitals»    [✔]

 
Nitrogen and oxygen:
O has a doubly filled «p-»orbital
OR
N has only singly occupied «p-»orbitals     [✔]
 
Note: Accept “greater e– - e- repulsion in O” or “lower e– - e- repulsion in N”.
Accept box annotation of electrons for M2.
11g. [1 mark]
The Lewis (electron dot) structure of the dinitrogen monoxide molecule can be
represented as:

State what the presence of alternative Lewis structures shows about the nature of the
bonding in the molecule.

Markscheme
delocalization
OR
delocalized π-electrons    [✔]
 
Note: Accept “resonance”.
11h. [1 mark]
State, giving a reason, the shape of the dinitrogen monoxide molecule.

Markscheme
linear AND 2 electron domains
OR
linear AND 2 regions of electron density    [✔]
 
Note: Accept “two bonds AND no lone pairs” for reason.
11i. [1 mark]
Deduce the hybridization of the central nitrogen atom in the molecule.

Markscheme
sp     [✔]
12a. [1 mark]
Rhenium, Re, was the last element with a stable isotope to be isolated.
The stable isotope of rhenium contains 110 neutrons.

State the nuclear symbol notation ❑ZA X for this isotope.

Markscheme
❑185
75 ℜ    [✔]

12b. [2 marks]
Before its isolation, scientists predicted the existence of rhenium and some of its
properties.
Suggest the basis of these predictions.
Markscheme
gap in the periodic table
OR
element with atomic number «75» unknown
OR
break/irregularity in periodic trends     [✔]
«periodic table shows» regular/periodic trends «in properties»      [✔]
12c. [2 marks]
A scientist wants to investigate the catalytic properties of a thin layer of rhenium metal on
a graphite surface.

Describe an electrochemical process to produce a layer of rhenium on graphite.

Markscheme
electrolyze «a solution of /molten» rhenium salt/Re n+     [✔]
graphite as cathode/negative electrode
OR
rhenium forms at cathode/negative electrode     [✔]
 
Note: Accept “using rhenium anode” for M1.
12d. [2 marks]
Predict two other chemical properties you would expect rhenium to have, given its position
in the periodic table.
Markscheme
Any two of:
variable oxidation states     [✔]
forms complex ions/compounds     [✔]
coloured compounds/ions     [✔]
«para»magnetic compounds/ions     [✔]
 
Note: Accept other valid responses related to its chemical metallic properties.
Do not accept “catalytic properties”.
12e. [2 marks]
Describe how the relative reactivity of rhenium, compared to silver, zinc, and copper, can
be established using pieces of rhenium and solutions of these metal sulfates.

Markscheme
place «pieces of» Re into each solution    [✔]
if Re reacts/is coated with metal, that metal is less reactive «than Re»    [✔]
 
Note: Accept other valid observations such as “colour of solution fades” or “solid/metal
appears” for “reacts”.
12f. [1 mark]
One chloride of rhenium has the empirical formula ReCl3.
State the name of this compound, applying IUPAC rules.

Markscheme
rhenium(III) chloride
OR
rhenium trichloride    [✔]
12g. [2 marks]
Calculate the percentage, by mass, of rhenium in ReCl 3.

Markscheme
«Mr ReCl3 = 186.21 + (3 × 35.45) =» 292.56    [✔]
186.21
«100 ×  =» 63.648 «%»   [✔]
292.56
12h. [1 mark]
Rhenium forms salts containing the perrhenate(VII) ion, ReO4−.
Suggest why the existence of salts containing an ion with this formula could be predicted.
Refer to section 6 of the data booklet.
Markscheme
same group as Mn «which forms MnO4-»
OR
in group 7/has 7 valence electrons, so its «highest» oxidation state is +7    [✔]
12i. [1 mark]
Deduce the coefficients required to complete the half-equation.
ReO4− (aq) + ____H+ (aq) + ____e− ⇌ [Re(OH)2]2+ (aq) + ____H2O (l)        Eθ = +0.36 V

Markscheme
ReO4− (aq) + 6H+ (aq) + 3e− ⇌ [Re(OH)2]2+ (aq) + 2H2O (l)    [✔]
12j. [1 mark]
Predict, giving a reason, whether the reduction of ReO4− to [Re(OH)2]2+ would oxidize Fe2+ to
Fe3+ in aqueous solution. Use section 24 of the data booklet.

Markscheme
no AND ReO4− is a weaker oxidizing agent than Fe3+
OR
no AND Fe3+ is a stronger oxidizing agent than ReO4−
OR
no AND Fe2+ is a weaker reducing agent than [Re(OH)2]2+
OR
no AND [Re(OH)2]2+ is a stronger reducing agent than Fe2+
OR
no AND cell emf would be negative/–0.41 V     [✔]
13a. [1 mark]
Nuclear medicine uses small amounts of radioisotopes to diagnose and treat some diseases.
State two common side effects of radiotherapy.

Markscheme
Any two of:
hair loss
fatigue
nausea
sterility
skin reaction
diarrhoea
vomiting
damage to lymph system
urinary/bladder changes
anxiety/emotional problems
joint/muscular stiffness
loss of appetite
sore/dry mouth
loss of weight
secondary cancer ✔
13b. [2 marks]
Explain why technetium-99m is the most common radioisotope used in nuclear medicine.

Markscheme
Any two of:
half-life is 6 hours/long enough for a scan to occur
OR
half-life short enough not to remain in body ✔
NOTE: Accept “short half-life so patient is not exposed to lots of ionizing radiation”.
decay releases «low energy» gamma rays
OR
gamma rays less likely to be absorbed by cells ✔
can form several «coordination» complexes ✔
NOTE: Accept "can exist in many oxidation states «so can form multiple complexes»" OR
"chemically versatile «so can act as a tracer by bonding to several bioactive compounds»”.

«low-energy» radiation/gamma-rays can be detected by common X-ray equipment ✔

13c. [2 marks]
25.0 μg of iodine-131, with a half-life of 8.00 days, was left to decay.
Calculate the mass of iodine-131, in μg, remaining after 32.0 days. Use section 1 of the data
booklet.

Markscheme
ALTERNATIVE 1
4 half-lives ✔
1.56 «μg of iodine-131 remain» ✔
 
ALTERNATIVE 2
1 32.0
()
m = 25.0  8.00 ✔
2
1.56 «μg of iodine-131 remain» ✔
 
ALTERNATIVE 3
ln 2
λ = «  » = 8.66 × 10−2 «day−1» ✔
8.00
−2
m = « 25.0 e −8.66 ×10 × 32.0=¿ » 1.56 «μg of iodine-131 remain» ✔

 
Award [2] for correct final answer.
14. [1 mark]
Which statement about 56Fe3+ and 54Fe2+ is correct?
 
A. Both have the same numbers of protons and electrons.
B. Both have the same number of protons.
C. Both have the same number of neutrons.
D. Both have the same numbers of protons and neutrons.

Markscheme
B
15. [1 mark]
Which shows the number of subatomic particles in 31P3−?

Markscheme
A
16. [1 mark]
What is the composition of the nucleus of 26Mg?
Markscheme
D
17a. [1 mark]
Calcium carbide, CaC2, is an ionic solid.
Describe the nature of ionic bonding.

Markscheme
electrostatic attraction AND oppositely charged ions
[1 mark]
17b. [2 marks]
Describe how the relative atomic mass of a sample of calcium could be determined from its
mass spectrum.

Markscheme
multiply relative intensity by «m/z» value of isotope
OR
find the frequency of each isotope
 
sum of the values of products/multiplication «from each isotope»
OR
find/calculate the weighted average
 
Award [1 max] for stating “m/z values of isotopes AND relative abundance/intensity” but
not stating these need to be multiplied.
[2 marks]
17c. [2 marks]
When calcium compounds are introduced into a gas flame a red colour is seen; sodium
compounds give a yellow flame. Outline the source of the colours and why they are
different.

Markscheme
«promoted» electrons fall back to lower energy level
energy difference between levels is different
 
Accept “Na and Ca have different nuclear charge” for M2.
[2 marks]
17d. [2 marks]
Suggest two reasons why solid calcium has a greater density than solid potassium.
Markscheme
Any two of:
stronger metallic bonding
smaller ionic/atomic radius
 
two electrons per atom are delocalized
OR
greater ionic charge
 
greater atomic mass
 
Do not accept just “heavier” or “more massive” without reference to atomic mass.
[2 marks]
17e. [1 mark]
Outline why solid calcium is a good conductor of electricity.

Markscheme
delocalized/mobile electrons «free to move»
 
 
[1 mark]
17f. [2 marks]
Sketch a graph of the first six ionization energies of calcium.
Markscheme

general increase
only one discontinuity between “IE2” and “IE3”
[2 marks]
17g. [1 mark]
Calcium carbide reacts with water to form ethyne and calcium hydroxide.
CaC2(s) + H2O(l) → C2H2(g) + Ca(OH)2(aq)
Estimate the pH of the resultant solution.
Markscheme
pH > 7
 
Accept any specific pH value or range of values above 7 and below 14.
[1 mark]
17h. [2 marks]
Describe how sigma (σ) and pi (π) bonds are formed.

Markscheme
sigma (σ):
overlap «of atomic orbitals» along the axial/internuclear axis
OR
head-on/end-to-end overlap «of atomic orbitals»
 
pi (π):
overlap «of p-orbitals» above and below the internuclear axis
OR
sideways overlap «of p-orbitals»
 
Award marks for suitable diagrams.
 
[2 marks]
17i. [1 mark]
Deduce the number of σ and π bonds in a molecule of ethyne.

Markscheme
sigma (σ): 3
AND
pi (π): 2
[1 mark]
18. [1 mark]
What is the number of protons and the number of neutrons in 131I?
Markscheme
A
19. [1 mark]
In which set do all the species contain more electrons than neutrons?
A.     14N, 16O, 11C
B.     14N, 16O, 11C4–
C.     14N3–, 16O2–, 11C
D.     14N3–, 16O2–, 11C4+

Markscheme
C
20. [1 mark]

What does ❑24

12 M g
2+¿ ¿
represent?

A.     An ion with 12 protons and 24 neutrons

B.     An ion with 14 protons and 24 neutrons
C.     An ion with 12 protons and 12 neutrons
D.     An ion with 12 protons and 22 neutrons

Markscheme
C

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