| Date | May 2017 | Marks available | 2 | Reference code | 17M.2.hl.TZ2.4 |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Explain | 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) N2O4(g)
At 100°C, the equilibrium constant, Kc, is 0.21.
Bonds can be formed in many ways.
Discuss the bonding in the resonance structures of ozone.
Deduce one resonance structure of ozone and the corresponding formal charges on each oxygen atom.
The first six ionization energies, in kJ mol–1, of an element are given below.
Explain the large increase in ionization energy from IE3 to IE4.
At a given time, the concentration of NO2(g) and N2O4(g) were 0.52 and respectively.
Deduce, showing your reasoning, if the forward or the reverse reaction is favoured at this time.
Comment on the value of ΔG when the reaction quotient equals the equilibrium constant, Q = K.
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/ electrons are delocalized/not localized”.
[3 marks]
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]
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]
«Qc = =» 0.37
reaction proceeds to the left/NO2(g) «until Q = Kc»
OR
reverse reaction «favoured»
Do not award M2 without a calculation for M1 but remember to apply ECF.
[2 marks]
ΔG = 0
reaction at equilibrium
OR
rate of forward and reverse reaction is the same
OR
constant macroscopic properties
[2 marks]
Examiners report
Syllabus sections
-
17M.1.hl.TZ1.5:
Which statement explains one of the decreases in first ionization energy (I.E.) across period 3?
A. The nuclear charge of element Al is greater than element Mg.
B. The electron-electron repulsion is greater, for the electron with the opposite spin, in element S than in element P.
C. A new sub-level is being filled at element S.
D. The p orbital being filled in element Al is at a lower energy than the s orbital in element Mg.
-
22M.1.hl.TZ1.5:
The graph shows the first six ionization energies of an element.
[Ionization energies of the elements (data page) Available at: https://en.wikipedia.org/wiki/Ionization_energies_of_the_
elements_(data_page) Text is available under the Creative Commons Attribution-ShareAlike License 3.0 (CC BY-SA
3.0) https://creativecommons.org/licenses/by-sa/3.0/deed.en.]
In which group is the element?A. 13
B. 14
C. 15
D. 16
- 18M.1.hl.TZ2.5: The graph shows the first ionization energies of some consecutive elements. Which...
- 18M.1.hl.TZ1.5: Which transition on the diagram corresponds to the ionization of hydrogen in the ground state?
-
18M.2.hl.TZ1.2e:
Sketch a graph of the first six ionization energies of calcium.
-
17M.2.hl.TZ1.2d.iv:
Explain why an aluminium-titanium alloy is harder than pure aluminium.
- 16N.1.hl.TZ0.6: A period 3 element, M, forms an oxide of the type M2O. Which represents the first four...
- 18N.1.hl.TZ0.5: The values for the first three successive ionization energies for two elements X and Z are...
- 18N.2.hl.TZ0.4c: Sketch a graph to show the relative values of the successive ionization energies of boron.
- 19M.1.hl.TZ1.5: Which element is represented by the first eight successive ionization energies on the...
-
19M.1.hl.TZ2.5:
Which of the following transitions in the hydrogen atom emits the least energy?
A. n = 2 to n = 1
B. n = 3 to n = 1
C. n = 4 to n = 2
D. n = 4 to n = 3
-
17N.1.hl.TZ0.6:
The graph represents the first ten ionisation energies (IE) of an element.
What is the element?
A. O
B. S
C. Ne
D. Cl
-
18M.2.hl.TZ2.3a.iii:
Hydrogen spectral data give the frequency of 3.28 × 1015 s−1 for its convergence limit.
Calculate the ionization energy, in J, for a single atom of hydrogen using sections 1 and 2 of the data booklet.
-
16N.2.hl.TZ0.4d:
(i) Explain the convergence of lines in a hydrogen emission spectrum.
(ii) State what can be determined from the frequency of the convergence limit.
-
19M.2.hl.TZ1.3a:
Plot the relative values of the first four ionization energies of sodium.
-
17M.2.hl.TZ1.2d.iii:
Sketch a graph of the first six successive ionization energies of vanadium on the axes provided.
-
19N.2.hl.TZ0.1e(ii):
Determine, showing your working, the wavelength, in m, of ultraviolet light absorbed by a single molecule in one of these steps. Use sections 1, 2 and 11 of the data booklet.
- 19N.1.hl.TZ0.5: Which shows the first ionization energies of successive elements across period 2, from left...
- 21M.1.hl.TZ1.6: The diagram shows the first ionisation energies of consecutive elements in the same period of...
- 21M.2.hl.TZ1.1c: Sketch the first eight successive ionisation energies of sulfur.
- 21M.1.hl.TZ2.5: The first eight successive ionization energies for an element are shown. In which group is...
-
19M.2.hl.TZ2.3c:
Explain why the first ionization energy of nitrogen is greater than both carbon and oxygen.
Nitrogen and carbon:
Nitrogen and oxygen:
- 22M.2.hl.TZ2.5a(ii): Explain why there is a large increase from the 8th to the 9th ionization energy of iron.
- 20N.1.hl.TZ0.5: Which element is in group 13?
-
20N.2.hl.TZ0.6a:
The electron configuration of copper makes it a useful metal.
Determine the frequency of a photon that will cause the first ionization of copper. Use sections 1, 2 and 8 of the data booklet.
-
21M.2.hl.TZ2.2a(ii):
Explain why the first ionization energy of sulfur is lower than that of phosphorus.
- 22M.2.hl.TZ1.1e(iv): Suggest, giving a reason, whether magnesium or nitrogen would have the greater sixth...
-
21N.2.hl.TZ0.2b:
Sodium emits yellow light with a frequency of 5.09 × 1014 Hz when electrons transition from 3p to 3s orbitals.
Calculate the energy difference, in J, between these two orbitals using sections 1 and 2 of the data booklet.
Darling, D, n.d. D lines (of sodium). [online] Available at <https://www.daviddarling.info/encyclopedia/D/D_lines.html> [Accessed 6 May 2020].
- 21N.1.hl.TZ0.5: Which statement explains why the second ionization energy of aluminium is higher than the...
