| Date | May 2022 | Marks available | 1 | Reference code | 22M.1.sl.TZ2.20 |
| Level | SL | Paper | 1 | Time zone | TZ2 |
| Command term | Deduce | Question number | 20 | Adapted from | N/A |
Question
What is the strongest acid in the equation below?
H3AsO4 + H2O H2AsO4− + H3O+ Kc = 4.5 × 10−4
A. H3AsO4
B. H2O
C. H2AsO4−
D. H3O+
Markscheme
D
Examiners report
A challenging question that combined interpreting the implications of the value of the equilibrium constant with the Brønsted-Lowry concept. Most candidates focused on BL theory and the forward reaction only. 36% of the candidates answered the question correctly by selecting the acid involved in the backward reaction.
Syllabus sections
- 17N.2.hl.TZ0.1e: Suggest why the enthalpy change of neutralization of CH3COOH is less negative than that of HCl.
- 18M.1.sl.TZ2.20: Which statement is correct? A. A strong acid is a good proton donor and has a strong...
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18N.2.hl.TZ0.6a.i:
State the equation for the reaction of each substance with water.
- 22M.2.sl.TZ2.3c(ii): State the meaning of a strong Brønsted–Lowry acid.
- 16N.2.sl.TZ0.2a: Distinguish between a weak acid and a strong acid. Weak acid: Strong acid:
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17M.1.sl.TZ1.20:
Which 1.0 moldm–3 solution has the highest pH?
A. Ammonium chloride
B. Sulfuric acid
C. Sodium chloride
D. Ammonia
-
22M.1.sl.TZ2.30:
20 cm3 of 1 mol dm−3 sulfuric acid was added dropwise to 20 cm3 of 1 mol dm−3 barium hydroxide producing a precipitate of barium sulfate.
H2SO4 (aq) + Ba(OH)2 (aq) → 2H2O (l) + BaSO4 (s)
Which graph represents a plot of conductivity against volume of acid added?
-
19N.2.sl.TZ0.4a(iii):
The dissociation of citric acid is an endothermic process. State the effect on the hydrogen ion concentration, [H+], and on the equilibrium constant, of increasing the temperature.
- 19N.2.sl.TZ0.4a(ii): The value of the equilibrium constant for the first dissociation at 298 K is 5.01 ×...
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18M.2.sl.TZ1.5a:
Predict, giving a reason, a difference between the reactions of the same concentrations of hydrochloric acid and ethanoic acid with samples of calcium carbonate.
-
18M.2.hl.TZ1.5a:
Predict, giving a reason, a difference between the reactions of the same concentrations of hydrochloric acid and ethanoic acid with samples of calcium carbonate.
-
17M.2.hl.TZ2.8b.v:
State a technique other than a pH titration that can be used to detect the equivalence point.
- 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.
-
18N.1.sl.TZ0.20:
What is the order of increasing pH for the following solutions of the same concentration?
A. HCl (aq) < NH3 (aq) < NaOH (aq) < CH3COOH (aq)
B. CH3COOH (aq) < HCl (aq) < NH3 (aq) < NaOH (aq)
C. HCl (aq) < CH3COOH (aq) < NH3 (aq) < NaOH (aq)
D. NaOH (aq) < NH3 (aq) < CH3COOH (aq) < HCl (aq)
-
19M.2.hl.TZ1.5a:
Outline why ethanoic acid is classified as a weak acid.
-
17M.2.sl.TZ1.4c:
Hydrazine reacts with water in a similar way to ammonia. Deduce an equation for the reaction of hydrazine with water.
-
17M.3.hl.TZ2.4a:
Identify the other product formed.
- 19N.2.sl.TZ0.4b: Outline one laboratory methods of distinguishing between solutions of citric acid and...
-
19M.2.sl.TZ2.5a(i):
Distinguish between a weak and strong acid.
Weak acid:
Strong acid:
-
19N.3.sl.TZ0.16a:
Identify the compound responsible for the acidity of gastric juice, and state whether it is a strong or weak acid.
-
19N.2.hl.TZ0.4a(iii):
The dissociation of citric acid is an endothermic process. State the effect on the hydrogen ion concentration, [H+], and on Ka, of increasing the temperature.
- 19N.2.hl.TZ0.4a(ii): The value of Ka at 298 K for the first dissociation is 5.01 × 10−4. State, giving a reason,...
- 19N.2.hl.TZ0.4b: Outline two laboratory methods of distinguishing between solutions of citric acid and...
-
17M.2.sl.TZ1.4d:
Outline, using an ionic equation, what is observed when magnesium powder is added to a solution of ammonium chloride.
-
19M.2.sl.TZ1.5a:
Outline why ethanoic acid is classified as a weak acid.
-
18M.2.sl.TZ2.2b.ii:
State and explain the effect on the rate of reaction if ethanoic acid of the same concentration is used in place of hydrochloric acid.
-
17M.3.sl.TZ2.14b.ii:
Describe how large amounts of CO2 could reduce the pH of the ocean using an equation to support your answer.
-
19M.2.hl.TZ2.5a(i):
Distinguish between a weak and strong acid.
Weak acid:
Strong acid:
-
21M.2.sl.TZ1.2b(ii):
Saturated aqueous hydrogen sulfide has a concentration of 0.10 mol dm−3 and a pH of 4.0. Demonstrate whether it is a strong or weak acid.
-
20N.1.sl.TZ0.20:
Which of these acids has the weakest conjugate base?
A.
B.
C.
D.
- 20N.2.sl.TZ0.1c(i): Hypochlorous acid is considered a weak acid. Outline what is meant by the term weak acid.
- 20N.2.hl.TZ0.1c(i): Hypochlorous acid is considered a weak acid. Outline what is meant by the term weak acid.
-
17M.3.sl.TZ2.14b.i:
Oceans can act as a carbon sink, removing some CO2(g) from the atmosphere.
CO2(g) CO2(aq)
Aqueous carbon dioxide, CO2(aq), quickly reacts with ocean water in a new equilibrium reaction. Construct the equilibrium equation for this reaction including state symbols.
- 21N.1.sl.TZ0.20: Which ions are present in an aqueous solution of Na2CO3? I. HCO3−II. OH−III. CO32− A. I...
