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Date	May 2019	Marks available	1	Reference code	19M.2.sl.TZ2.3
Level	SL	Paper	2	Time zone	TZ2
Command term	Suggest	Question number	3	Adapted from	N/A

Question

Dinitrogen monoxide, N₂O, causes depletion of ozone in the stratosphere.

Different sources of N₂O have different ratios of ¹⁴N:¹⁵N.

Outline why ozone in the stratosphere is important.

[1]

State one analytical technique that could be used to determine the ratio of ¹⁴N:¹⁵N.

[1]

b(i).

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.

[2]

b(ii).

Predict, giving two reasons, how the first ionization energy of ¹⁵N compares with that of ¹⁴N.

[2]

b(iii).

Suggest why it is surprising that dinitrogen monoxide dissolves in water to give a neutral solution.

[1]

Markscheme

absorbs UV/ultraviolet light «of longer wavelength than absorbed by O₂» [✔]

mass spectrometry/MS [✔]

b(i).

« $\frac{{(98 \times 14) + (2 \times 15)}}{{100}} =$ » 14.02 [✔]

«M_r = (14.02 × 2) + 16.00 =» 44.04 [✔]

b(ii).

Any two:
same AND have same nuclear charge/number of protons/Z_eff [✔]

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.

b(iii).

oxides of nitrogen/non-metals are «usually» acidic [✔]

Examiners report

60 % of the candidates were aware that ozone in the atmosphere absorbs UV light. Some candidates did not gain the mark for not specifying the type of radiation absorbed.

Well answered. More than half of the candidates stated mass spectrometry is used to determine the ratio of the isotopes.

b(i).

Many candidates successfully calculated the relative atomic mass of nitrogen in the sample. M2 was awarded independently of M1, so candidates who calculated the relative molecular mass using the A_r of nitrogen in the data booklet (14.01) were awarded M2. Many candidates scored both marks.

b(ii).

This was a challenging question for many candidates, while stronger candidates often showed clarity of thinking and were able to conclude that the ionization energies of the two isotopes must be the same and to provide two different reasons for this. Some candidates did realize that the ionization energies are similar but did not give the best reasons to support their answer. Many candidates thought the ionization energies would be different because the size of the nucleus was different. Some teachers commented that the question was difficult while others liked it because it made students apply their knowledge in an unfamiliar situation. The question had a good discrimination index.

b(iii).

Only a quarter of the candidates answered correctly. Some simply stated that N₂O forms HNO₃ with water which did not gain the mark.

Syllabus sections

Core » Topic 3: Periodicity » 3.2 Periodic trends

Show 78 related questions

18M.1.sl.TZ1.7: Which describes the oxide of sodium, Na2O?
18M.1.sl.TZ1.8: Which statement is correct? A. Atomic radius decreases down group 17. B. First...
18M.1.sl.TZ2.7: Which increase across a period from left to right?
18M.2.sl.TZ2.3b.ii:
Outline why the ionic radius of K⁺ is smaller than that of Cl⁻.
18M.2.sl.TZ2.3b.i:
Outline why atomic radius decreases across period 3, sodium to chlorine.
22M.2.sl.TZ2.1d: Describe two observations that indicate the reaction of lithium with water is exothermic.
22M.2.hl.TZ1.5d(iv): The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–. Outline, giving a...
17N.2.sl.TZ0.2a: Explain the general increasing trend in the first ionization energies of the period...
17N.1.sl.TZ0.8: Which oxide dissolves in water to give a solution with a pH below 7? A. MgO B. Li2O C....
22M.2.hl.TZ1.1a(ii): Identify a metal, in the same period as magnesium, that does not form a basic oxide.
22M.2.hl.TZ1.1e(iii):
The nitride ion and the magnesium ion are isoelectronic (they have the same electron configuration). Determine, giving a reason, which has the greater ionic radius.
16N.2.sl.TZ0.4d: Describe the trend in acid-base properties of the oxides of period 3, sodium to chlorine.
22M.1.sl.TZ2.7: Three elements, X, Y, and Z are in the same period of the periodic table. The relative sizes...
17M.1.sl.TZ2.12: Which metal has the strongest metallic bond? A. Li B. Na C. K D. Rb
17M.1.sl.TZ1.8: Which oxide, when added to water, produces the solution with the highest pH? A. Na2O B....
16N.1.sl.TZ0.8:
Which solution forms when phosphorus(V) oxide, P₄O₁₀, reacts with water?
22M.1.hl.TZ2.6: Which are the most reactive elements of the alkali metals and halogens? A. Lithium and...
22M.1.hl.TZ2.5: What is the correct order for increasing first ionization energy? A. Na < Mg <...
19M.2.hl.TZ2.4e(i):
Suggest why the existence of salts containing an ion with this formula could be predicted. Refer to section 6 of the data booklet.
22M.2.sl.TZ2.2a:
Explain why the first ionization energy of calcium is greater than that of potassium.
18M.2.sl.TZ1.2d.i:
Suggest two reasons why solid calcium has a greater density than solid potassium.
21N.1.sl.TZ0.7: Which element has the highest metallic character in Group 14? A. C B. Si C. Ge D. Sn
18M.2.sl.TZ1.2e:
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.
21N.1.sl.TZ0.8: Which combination describes the acid–base nature of aluminium and phosphorus oxides?
18N.1.sl.TZ0.7: Which oxides produce an acidic solution when added to water? I. Al2O3 and SiO2 II. ...
18N.1.sl.TZ0.8: Which species will require the least energy for the removal of one electron? A. ...
18N.2.hl.TZ0.4a: Explain the decrease in atomic radius from Na to Cl.
18N.2.sl.TZ0.4a: Explain the decrease in atomic radius from Na to Cl.
18N.2.hl.TZ0.4b: Explain why the radius of the sodium ion, Na+, is smaller than the radius of the oxide ion, O2−.
18N.2.sl.TZ0.4b.i: Explain why the radius of the sodium ion, Na+, is smaller than the radius of the oxide ion, O2−.
17M.1.hl.TZ1.6: What is the order of decreasing ionic radius? A. S2− > Cl− > Al3+ > Mg2+ B. ...
16N.1.hl.TZ0.7: Which property increases down group 17, the halogens? A. Electron affinity B. Boiling...
19M.1.hl.TZ1.7: Which series represents atoms in order of decreasing atomic radius? A. N > C > Be >...
16N.1.hl.TZ0.8: Which correctly describes the reaction between potassium and excess water? A. The reaction...
19M.3.hl.TZ1.1b(iv):
Sketch how the first ionization energies of elements vary with their atomic radius.
19M.3.sl.TZ1.1b(iv):
Sketch how the first ionization energies of elements vary with their atomic radius.
19M.1.sl.TZ1.8: What are typical characteristics of metals?
19M.1.sl.TZ2.8: How do the following properties change down Group 17 of the periodic table?
17M.2.sl.TZ2.1c.i:
Some oxides of period 3, such as Na₂O and P₄O₁₀, react with water. A spatula measure of each oxide was added to a separate 100 cm³ flask containing distilled water and a few drops of bromothymol blue indicator.

The indicator is listed in section 22 of the data booklet.

Deduce the colour of the resulting solution and the chemical formula of the product formed after reaction with water for each oxide.
17N.1.sl.TZ0.7:
Which trends are correct across period 3 (from Na to Cl)?

I. Atomic radius decreases
II. Melting point increases
III. First ionization energy increases

A. I and II only

B. I and III only

C. II and III only

D. I, II and III
17M.1.hl.TZ2.5: X, Y and Z represent the successive elements, Ne, Na and Mg, but not necessarily in that...
17M.2.sl.TZ1.2d.ii:
Explain why an aluminium-titanium alloy is harder than pure aluminium.
19N.1.sl.TZ0.7: Which property shows a general increase from left to right across period 2, Li to F? A. ...
16N.2.sl.TZ0.4e:
In addition to magnesium oxide, magnesium forms another compound when burned in air. Suggest the formula of this compound
17N.2.sl.TZ0.2c:
State an equation for the reaction of phosphorus (V) oxide, P₄O₁₀ (s), with water.
17M.2.hl.TZ1.2d.ii:
Suggest why the melting point of vanadium is higher than that of titanium.
21N.1.hl.TZ0.6: Which ion has the largest radius? A. Na+ B. Mg2+ C. P3− D. S2−
18M.2.hl.TZ1.2d.i:
Suggest two reasons why solid calcium has a greater density than solid potassium.
17N.2.sl.TZ0.2b:
Explain why the melting points of the group 1 metals (Li → Cs) decrease down the group.
19M.2.hl.TZ1.3b:
Outline why the alkali metals (group 1) have similar chemical properties.
19M.2.sl.TZ2.4a:
Before its isolation, scientists predicted the existence of rhenium and some of its properties.

Suggest the basis of these predictions.
21M.1.sl.TZ1.8: Which trend is correct, going down group 1? A. Melting point increases B. Reactivity...
19N.2.sl.TZ0.6b:
Another airbag reactant produces nitrogen gas and sodium.

Suggest, including an equation, why the products of this reactant present a safety hazard.
16N.1.sl.TZ0.7:
Which equation represents the first electron affinity of chlorine?

A. Cl(g)+e^-→ Cl^-(g)
B. $\frac{1}{2}$ Cl₂(g) + e^- → Cl^-(g)
C. Cl⁺(g) + e^- → Cl(g)
D. Cl(g) → Cl⁺(g) + e^-
17N.2.hl.TZ0.3b:
Explain why the melting points of the group 1 metals (Li → Cs) decrease down the group whereas the melting points of the group 17 elements (F → I) increase down the group.
20N.1.hl.TZ0.6: What is the correct trend going down groups 1 and 17? A. Melting points increase B. Boiling...
19M.2.hl.TZ1.3e:
Write equations for the separate reactions of solid sodium oxide and solid phosphorus(V) oxide with excess water and differentiate between the solutions formed.

Sodium oxide, Na₂O:

Phosphorus(V) oxide, P₄O₁₀:

Differentiation:
22M.1.sl.TZ1.7: Which gases are acidic? I. nitrogen dioxideII. carbon dioxideIII. sulfur dioxide A. I...
22M.1.sl.TZ1.8:
Which of the following is the electron configuration of a metallic element?

A. [Ne] 3s² 3p²

B. [Ne] 3s² 3p⁴

C. [Ne] 3s² 3p⁶ 3d³ 4s²

D. [Ne] 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵
19M.2.sl.TZ1.3a(ii):
Write equations for the separate reactions of solid sodium oxide and solid phosphorus(V) oxide with excess water and differentiate between the solutions formed.

Sodium oxide, Na₂O:

Phosphorus(V) oxide, P₄O₁₀:

Differentiation:
19M.2.hl.TZ2.3b(iii):
Predict, giving two reasons, how the first ionization energy of ¹⁵N compares with that of ¹⁴N.
21M.2.hl.TZ1.1d(iv):
Outline, in terms of their electronic structures, why the ionic radius of the sulfide ion is greater than that of the oxide ion.
21M.1.sl.TZ2.7: Which property increases down group 1? A. atomic radius B. electronegativity C. first...
21M.2.sl.TZ1.1c(iii):
Outline, in terms of their electronic structures, why the ionic radius of the sulfide ion is greater than that of the oxide ion.
21M.2.sl.TZ2.2a(i): Explain why Si has a smaller atomic radius than Al.
20N.1.sl.TZ0.7:
Which of the following shows a general increase across period 3 from $Na$ to $Cl$ ?

A. Ionic radius

B. Atomic radius

C. Ionization energy

D. Melting point
21M.2.hl.TZ2.2a(i): Explain why Si has a smaller atomic radius than Al.
20N.2.sl.TZ0.1a(ii):
State, giving a reason, whether the chlorine atom or the chloride ion has a larger radius.
20N.1.sl.TZ0.8:
Which oxide will dissolve in water to give the solution with the lowest pH?

A.   $P_{4} O_{10}$

B.   ${SiO}_{2}$

C.   ${Al}_{2} O_{3}$

D.   $MgO$
20N.2.hl.TZ0.1a(iii):
Outline why the chlorine atom has a smaller atomic radius than the sulfur atom.
20N.2.hl.TZ0.1a(ii):
State, giving a reason, whether the chlorine atom or the chloride ion has a larger radius.
20N.2.sl.TZ0.1a(iii):
Outline why the chlorine atom has a smaller atomic radius than the sulfur atom.
18M.2.hl.TZ1.2f:
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.
22M.2.sl.TZ1.1a(iii): Identify a metal, in the same period as magnesium, that does not form a basic oxide.
22M.2.sl.TZ1.1e(iii):
The nitride ion and the magnesium ion are isoelectronic (they have the same electron configuration). Determine, giving a reason, which has the greater ionic radius.
22M.2.sl.TZ1.3f(iii): The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–. Outline, giving a...
21N.2.hl.TZ0.2a: Explain the general increase in trend in the first ionization energies of the period 3...
21N.2.sl.TZ0.2: Explain the general increase in trend in the first ionization energies of the period 3...

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