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Date	May 2017	Marks available	3	Reference code	17M.2.hl.TZ2.4
Level	HL	Paper	2	Time zone	TZ2
Command term	Discuss	Question number	4	Adapted from	N/A

Question

Bonds can be formed in many ways.

The equilibrium for a mixture of NO₂ and N₂O₄ gases is represented as:

2NO₂(g) $\rightleftharpoons$ N₂O₄(g)

At 100°C, the equilibrium constant, K_c, is 0.21.

Bonds can be formed in many ways.

Discuss the bonding in the resonance structures of ozone.

[3]

b.i.

Deduce one resonance structure of ozone and the corresponding formal charges on each oxygen atom.

[2]

b.ii.

The first six ionization energies, in kJ mol^–1, of an element are given below.

M17/4/CHEMI/HP2/ENG/TZ2/04.c

Explain the large increase in ionization energy from IE₃ to IE₄.

[2]

At a given time, the concentration of NO₂(g) and N₂O₄(g) were 0.52 and $0.10{\text{ mol}}\,{\text{d}}{{\text{m}}^{ - 3}}$ respectively.

Deduce, showing your reasoning, if the forward or the reverse reaction is favoured at this time.

[2]

d.i.

Comment on the value of ΔG when the reaction quotient equals the equilibrium constant, Q = K.

[2]

d.ii.

Markscheme

lone pair on p orbital «of O atom» overlaps/delocalizes with pi electrons «from double bond»

both O–O bonds have equal bond length
OR
both O–O bonds have same/1.5 bond order
OR
both O–O are intermediate between O–O AND O=O

both O–O bonds have equal bond energy

Accept “p/pi/ $\pi$ electrons are delocalized/not localized”.

[3 marks]

b.i.

ALTERNATIVE 1:

FC: –1 AND +1 AND 0

ALTERNATIVE 2:

FC: 0 AND +1 AND –1

Accept any combination of lines, dots or crosses to represent electrons.

Do not accept structure that represents 1.5 bonds.

Do not penalize missing lone pairs if already penalized in 3(b).

If resonance structure is incorrect, no ECF.

Any one of the structures with correct formal charges for [2 max].

[2 marks]

b.ii.

Any two of:
IE₄: electron in lower/inner shell/energy level
OR
IE₄: more stable/full electron shell

IE₄: electron closer to nucleus
OR
IE₄: electron more tightly held by nucleus

IE₄: less shielding by complete inner shells

Accept “increase in effective nuclear charge” for M2.

[2 marks]

«Q_c = $\frac{{0.10}}{{{{0.52}^2}}}$ =» 0.37
reaction proceeds to the left/NO₂(g) «until Q = K_c»
OR
reverse reaction «favoured»

Do not award M2 without a calculation for M1 but remember to apply ECF.

[2 marks]

d.i.

ΔG = 0
reaction at equilibrium
OR
rate of forward and reverse reaction is the same
OR
constant macroscopic properties

[2 marks]

d.ii.

Examiners report

[N/A]

b.i.

[N/A]

b.ii.

[N/A]

d.i.

[N/A]

d.ii.

Syllabus sections

Additional higher level (AHL) » Topic 14: Chemical bonding and structure » 14.1 Covalent bonding and electron domain and molecular geometries

Show 55 related questions

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18M.1.hl.TZ2.12: Which molecule has an expanded octet? A. CO B. CO2 C. SF2 D. SF4
18M.2.hl.TZ2.7c.ii:
Deduce, giving a reason, the more likely structure.
22M.1.hl.TZ2.11:
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A. −2

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22M.1.hl.TZ2.12: What is the molecular geometry of SF4? A. Tetrahedral B. Trigonal bipyramidal C. ...
17M.1.hl.TZ1.13: Which species have resonance structures? I. Ozone, O3II. Carbon dioxide, CO2III. ...
18M.1.hl.TZ2.13:
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18M.2.hl.TZ1.2g.ii:
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17M.2.hl.TZ2.4b.ii:
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18M.2.hl.TZ1.1i:
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22M.2.hl.TZ2.7b(i):
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17M.2.hl.TZ2.3b:
Deduce the Lewis (electron dot) structure and molecular geometry and the bond angles of PCl₃.
16N.2.hl.TZ0.5b:
(i) Draw diagrams to show how sigma (σ) and pi (π) bonds are formed between atoms.

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18N.1.hl.TZ0.12:
What is the number of sigma (σ) and pi (π) bonds in the molecule (NC)₂C=C(CN)₂?
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Draw two Lewis (electron dot) structures for BrO₃⁻.
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17M.2.hl.TZ1.8b:
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19M.1.hl.TZ2.12:
How many sigma (σ) and pi (π) bonds are present in hydrogen cyanide, HCN?
22M.2.hl.TZ2.7b(ii):
Identify the number of sigma and pi bonds in HCN.
18M.2.hl.TZ1.2g.i:
Describe how sigma (σ) and pi ( $\pi$ ) bonds are formed.
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16N.3.hl.TZ0.22c:
(i) Uranium hexafluoride, UF₆, is used in the uranium enrichment process that produces fuel for nuclear reactors.

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16N.1.hl.TZ0.14:
Which species has bond angles of 90°?

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B. ${\text{I}}$ Cl₄^-

C. NH₄⁺

D. SiCl₄
21N.1.hl.TZ0.12:
Which molecules contain two pi ( $π$ ) bonds?

I. HCN
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A. I and II only

B. I and III only

C. II and III only

D. I, II and III
19M.2.hl.TZ2.3d(i):
State what the presence of alternative Lewis structures shows about the nature of the bonding in the molecule.
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Formulate two equations to show how nitrogen(II) oxide, NO, catalyses the destruction of ozone.
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19M.2.hl.TZ1.2e:
Outline why both C to O bonds in the conjugate base are the same length and suggest a value for them. Use section 10 of the data booklet.
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Absorption of UV light in the ozone layer causes the dissociation of oxygen and ozone.

Identify, in terms of bonding, the molecule that requires a longer wavelength to dissociate.
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State the number of sigma ( $σ$ ) and pi ( $π$ ) bonds around the central carbon atom in molecule B.
19N.2.hl.TZ0.6f(iii):
When excess ammonia is added to copper(II) chloride solution, the dark blue complex ion, [Cu(NH₃)₄(H₂O)₂]²⁺, forms.

State the molecular geometry of this complex ion, and the bond angles within it.

Molecular geometry:

Bond angles:
21M.2.hl.TZ2.4d:
Draw diagrams to show how sigma (σ) and pi (π) bonds are formed between atoms.
19M.2.hl.TZ2.3a(ii):
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.
22M.2.hl.TZ1.6a(ii):
Deduce a Lewis (electron dot) structure of the nitric acid molecule, HNO₃, that obeys the octet rule, showing any non-zero formal charges on the atoms.
22M.2.hl.TZ1.5a(iii):
State the number of $σ$ (sigma) and $π$ (pi) bonds in Compound A.
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21N.2.hl.TZ0.10a(i):
Distinguish between a sigma and pi bond.

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Additional higher level (AHL) » Topic 14: Chemical bonding and structure

Additional higher level (AHL)

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Markscheme

Examiners report

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