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Date	May 2018	Marks available	1	Reference code	18M.2.sl.TZ2.2
Level	SL	Paper	2	Time zone	TZ2
Command term	Outline	Question number	2	Adapted from	N/A

Question

Graphing is an important tool in the study of rates of chemical reactions.

Excess hydrochloric acid is added to lumps of calcium carbonate. The graph shows the volume of carbon dioxide gas produced over time.

Sketch a Maxwell–Boltzmann distribution curve for a chemical reaction showing the activation energies with and without a catalyst.

[3]

Sketch a curve on the graph to show the volume of gas produced over time if the same mass of crushed calcium carbonate is used instead of lumps. All other conditions remain constant.

[1]

b.i.

State and explain the effect on the rate of reaction if ethanoic acid of the same concentration is used in place of hydrochloric acid.

[2]

b.ii.

Outline why pH is more widely used than [H⁺] for measuring relative acidity.

[1]

Outline why H₃PO₄/HPO₄²⁻ is not a conjugate acid-base pair.

[1]

Markscheme

M18/4/CHEMI/SP2/ENG/TZ2/02.a/M

both axes correctly labelled

correct shape of curve starting at origin

E_a(catalyst) < E_{a(without catalyst)} on x-axis

M1:

Accept “speed” for x-axis label.

Accept “number of particles”, “N”, “frequency” or “probability «density»” for y-axis label.

Do not accept “potential energy” for x-axis label.

M2:

Do not accept a curve that touches the x-axis at high energy.

Do not award M2 if two curves are drawn.

M3:

Ignore any shading under the curve.

[3 marks]

M18/4/CHEMI/SP2/ENG/TZ2/02.b.i/M

curve starting from origin with steeper gradient AND reaching same maximum volume

[1 mark]

b.i.

rate decreases

slower reaction

«ethanoic acid» partially dissociated/ionized «in solution/water»

lower [H⁺]

Accept “weak acid” or “higher pH”.

[2 marks]

b.ii.

«pH» converts «wide range of [H⁺]» into simple «log» scale/numbers

«pH» avoids need for exponential/scientific notation

«pH» converts small numbers into values «typically» between 0/1 and 14

«pH» allows easy comparison of values of [H⁺]

Accept “uses values between 0/1 and 14”.

Do not accept “easier to use”.

Do not accept “easier for calculations”.

[1 mark]

«species» do not differ by a «single» proton/H⁺

conjugate base of H₃PO₄ is H₂PO₄^– «not HPO₄^2–»

conjugate acid of HPO₄^2– is H₂PO₄^– «not H₃PO₄»

Do not accept “hydrogen/H” for “H⁺/proton”.

[1 mark]

Examiners report

[N/A]

b.i.

[N/A]

b.ii.

[N/A]

Syllabus sections

Core » Topic 8: Acids and bases » 8.1 Theories of acids and bases

Show 47 related questions

18M.1.sl.TZ1.19:
Which classification is correct for the reaction?

H₂PO₄⁻(aq) + H₂O(l) → HPO₄²⁻(aq) + H₃O⁺(aq)
22M.2.hl.TZ1.4a: State the relationship between NH4+ and NH3 in terms of the Brønsted–Lowry theory.
18N.2.hl.TZ0.6a.i:
State the equation for the reaction of each substance with water.
17N.2.sl.TZ0.5b.ii: State what is meant by the term conjugate base.
17N.2.sl.TZ0.5b.iii: State the conjugate base of the hydroxide ion, OH–.
17N.2.sl.TZ0.5b.i: Identify two different amphiprotic species in the above reactions.
17M.2.sl.TZ2.7a.ii:
Identify one conjugate acid-base pair in the reaction.
22M.2.sl.TZ2.3c(ii): State the meaning of a strong Brønsted–Lowry acid.
17M.1.sl.TZ1.19: Which is an acid-base conjugate pair? A. H3O+ / OH– B. H2SO4 / SO42– C. ...
17M.1.hl.TZ1.24: Which species produced by the successive dissociations of phosphoric acid, H3PO4,...
16N.1.sl.TZ0.19: Which species behave as Brønsted–Lowry bases in the following reaction? H2SO4 + HNO3...
17M.2.sl.TZ2.7a.i:
Identify the amphiprotic species.
19N.2.sl.TZ0.4a(i): Identify a conjugate acid–base pair in the equation.
18M.1.hl.TZ1.24: What describes HPO42−? A. Amphiprotic but not amphoteric B. Amphoteric but not...
18M.2.hl.TZ1.5c:
Write an equation to show ammonia, NH₃, acting as a Brønsted–Lowry base and a different equation to show it acting as a Lewis base.
22M.2.hl.TZ2.6d(ii): State the meaning of a strong Brønsted–Lowry acid.
18N.2.sl.TZ0.6a:
State the equation for the reaction of each substance with water.
21N.2.sl.TZ0.5a:
Formulate an equation for the reaction of one mole of phosphoric acid with one mole of sodium hydroxide.
21N.2.sl.TZ0.5d: Outline the reason that sodium hydroxide is considered a Brønsted–Lowry base.
17M.1.hl.TZ1.26:
Which species acts as a Lewis and Brønsted–Lowry base?

A. [Al(H₂O)₆]³⁺

B. BF₃

C. NH₄⁺

D. OH⁻
19M.2.sl.TZ2.5a(ii):
The hydrogencarbonate ion, produced in Equilibrium (2), can also act as an acid.

State the formula of its conjugate base.
17M.1.sl.TZ2.20: Which of the following is correct? A. A weak acid is a proton donor and its aqueous...
19N.2.hl.TZ0.4a(i): Identify a conjugate acid–base pair in the equation.
19N.3.sl.TZ0.1c(i): Justify this hypothesis.
17N.2.sl.TZ0.5c:
A student working in the laboratory classified HNO₃, H₂SO₄, H₃PO₄ and HClO₄ as acids based on their pH. He hypothesized that “all acids contain oxygen and hydrogen”.

Evaluate his hypothesis.
21N.2.hl.TZ0.5a:
Formulate an equation for the reaction of one mole of phosphoric acid with one mole of sodium hydroxide.
17M.2.sl.TZ2.7b.i:
Calculate the amount, in mol, of NaOH(aq) used.
19M.2.sl.TZ1.2a:
Draw the structure of the conjugate base of benzoic acid showing all the atoms and all the bonds.
19N.1.sl.TZ0.21: Which is an example of an amphiprotic species? A. Al2O3 B. CO32− C. P4O10 D. HPO42−
19N.1.sl.TZ0.20: What is the difference between a conjugate Brønsted–Lowry acid–base pair? A. Electron...
18N.1.sl.TZ0.19:
Which two species act as Brønsted–Lowry acids in the reaction?

H₂PO₄⁻ (aq) + OH⁻ (aq) $\rightleftharpoons$ HPO₄²⁻ (aq) + H₂O (l)

A. HPO₄²⁻ (aq) and OH⁻ (aq)

B. H₂PO₄⁻ (aq) and HPO₄²⁻ (aq)

C. HPO₄²⁻ (aq) and H₂O (l)

D. H₂PO₄⁻ (aq) and H₂O (l)
20N.2.hl.TZ0.5d:
Calculate the $K_{b}$ of the conjugate base of ethanoic acid using sections 2 and 21 of the data booklet.
19M.2.hl.TZ2.5a(ii):
The hydrogencarbonate ion, produced in Equilibrium (2), can also act as an acid.

State the formula of its conjugate base.
19M.2.hl.TZ2.5e:
The reaction of the hydroxide ion with carbon dioxide and with the hydrogencarbonate ion can be represented by Equations 3 and 4.

Equation (3) OH⁻ (aq) + CO₂ (g) → HCO₃⁻ (aq)
Equation (4) OH⁻ (aq) + HCO₃⁻ (aq) → H₂O (l) + CO₃²⁻ (aq)

Discuss how these equations show the difference between a Lewis base and a Brønsted–Lowry base.

Equation (3):

Equation (4):
21N.2.hl.TZ0.5d: Outline the reasons that sodium hydroxide is considered a Brønsted–Lowry and Lewis base.
21M.1.hl.TZ1.26:
Which is a Lewis acid, but not a Brønsted-Lowry acid?

A.   ${BF}_{3}$

B.   $H_{3} O^{+}$

C.   ${NH}_{3}$

D.   ${Cl}^{-}$
19M.2.hl.TZ1.2d:
Draw the structure of the conjugate base of benzoic acid showing all the atoms and all the bonds.
21M.1.sl.TZ2.19: Which cannot act as a Brønsted–Lowry base? A. HPO42− B. H2O C. CH4 D. NH3
21M.2.sl.TZ1.2b(i): State the formula of its conjugate base.
20N.1.sl.TZ0.20:
Which of these acids has the weakest conjugate base?

A.   $HCl$

B.   ${CH}_{3} COOH$

C.   ${NH}_{4} Cl$

D.   $C_{6} H_{5} COOH$
20N.2.sl.TZ0.1c(ii):
State the formula of the conjugate base of hypochlorous acid.
20N.2.hl.TZ0.1c(ii):
State the formula of the conjugate base of hypochlorous acid.
20N.1.hl.TZ0.26:
Which species is a Lewis acid but not a Brønsted–Lowry acid?

A.   ${Cu}^{2 +}$

B.   ${NH}_{4}^{+}$

C.   $Cu$

D.   ${CH}_{3} COOH$
22M.2.sl.TZ1.2e(i): State the relationship between NH4+ and NH3 in terms of the Brønsted–Lowry theory.
21N.2.hl.TZ0.5b:
Formulate two equations to show the amphiprotic nature of H₂PO₄⁻.
21N.1.sl.TZ0.21: What is the conjugate acid of HS−? A. H2S B. S2− C. H2SO3 D. H2SO4
21N.2.sl.TZ0.5b:
Formulate two equations to show the amphiprotic nature of H₂PO₄⁻.

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