What will happen if the pressure is increased in the following reaction mixture at equilibrium?

CO₂ (g) + H₂O (l) $\rightleftharpoons$ H⁺ (aq) + HCO₃⁻ (aq)

A. The equilibrium will shift to the right and pH will decrease.

B. The equilibrium will shift to the right and pH will increase.

C. The equilibrium will shift to the left and pH will increase.

D. The equilibrium will shift to the left and pH will decrease.

A

Which classification is correct for the reaction?

H₂PO₄⁻(aq) + H₂O(l) → HPO₄²⁻(aq) + H₃O⁺(aq)

D

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)

D

Which apparatus can be used to monitor the rate of this reaction?

${\mathrm{CH}}_3{\mathrm{COCH}}_3 \left(\mathrm{aq}\right)+{\mathrm{I}}_2 \left(\mathrm{aq}\right)\to {\mathrm{CH}}_3{\mathrm{COCH}}_2\mathrm{I} \left(\mathrm{aq}\right)+{\mathrm{H}}^{+} \left(\mathrm{aq}\right)+{\mathrm{I}}^{-} \left(\mathrm{aq}\right)$

1. A pH meter
2. A gas syringe
3. A colorimeter
   

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

B

It was pleasing to see that a vast majority of candidates could select equipment necessary to monitor rates of reaction. This was one of the best answered questions in the exam.

Which is not a source of oxides of sulfur and nitrogen?

A. burning coal

B. internal combustion engines

C. burning methane

D. volcanic eruptions

C

One teacher thought this was a tricky question if candidates did not think of impurities in the combustion. However, 64 % of candidates answered correctly.

What is the major reason why the pH of unpolluted rain is less than 7?

A. methane

B. carbon dioxide

C. nitrogen oxides

D. sulfur dioxide

B

This was one of the challenging questions on the paper. 58 % of the candidates identified carbon dioxide as the cause of acidity in unpolluted rain. The rest mainly chose either nitrogen oxides (option C) or sulfur dioxide (option D), the causes of acidity in polluted rain.

Activity series of selected elements:

$$\text{greatest activity}\stackrel{\text{K, Ca, Al, Fe, H, Cu, Ag, Au}}{\leftarrow }\text{least activity}$$

Which react with dilute sulfuric acid?

       I.     Cu

       II.     CuO

       III.     CuCO₃

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

C

Which statement is correct?

A.     A strong acid is a good proton donor and has a strong conjugate base.

B.     A weak acid is a poor proton acceptor and has a strong conjugate base.

C.     A strong acid is a good proton donor and has a weak conjugate base.

D.     A strong base is a good proton donor and has a weak conjugate acid.

C

Which 0.01 mol dm^–3 aqueous solution has the highest pH?

A.  HCl

B.  H₂SO₄

C.  NaOH

D.  NH₃

C

A student carried out a titration to determine the concentration of an acid and found that his value had good precision but poor accuracy. Which process explains this outcome?

A. Consistently overshooting the volume of solution from the burette into the flask.

B. Collection of insufficient titration data.

C. Reading the meniscus in the burette at a different angle each time.

D. Forgetting to rinse the flask after one of the titrations.

A

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)

C

Which solution is basic at 25 °C?

K_w = 1.0 × 10⁻¹⁴

A. [H⁺] = 1.0 × 10⁻³ mol dm⁻³

B. [OH⁻] = 1.0 × 10⁻¹³ mol dm⁻³

C. solution of pH = 4.00

D. [H₃O⁺] = 1.0 × 10⁻¹³ mol dm⁻³

D

This was very poorly answered and had one of the highest discriminatory indices. More candidates thought that a basic solution would have [OH^- ] = 1.0 x 10^-13 mol dm^-3 , rather than [H₃O⁺ ] = 1.0 x 10^-13 mol dm^-3

What is the conjugate acid of HS⁻?

A.  H₂S

B.  S²⁻

C.  H₂SO₃

D.  H₂SO₄

A

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?

B

The question involved the formation of a precipitate – not a familiar concept to the candidates. It required candidates (to work out how the number of ions and hence conductivity were changing. 37% of the candidates got the correct answer (conductivity decreased as volume of H₂SO₄ increased). The majority increased conductivity as H₂SO₄ was added.

Which cannot act as a Brønsted–Lowry base?

A.  HPO₄²⁻

B.  H₂O

C.  CH₄

D.  NH₃

C

What occurs when solid sodium hydrogen carbonate reacts with aqueous sulfuric acid? 

A. Bubbles of sulfur dioxide form. 

B. Bubbles of both hydrogen and carbon dioxide form. 

C. Bubbles of hydrogen form. 

D. Bubbles of carbon dioxide form.

D

Which of these acids has the weakest conjugate base?

A.  $\mathrm{HCl}$

B.  ${\mathrm{CH}}_3\mathrm{COOH}$

C.  ${\mathrm{NH}}_4\mathrm{Cl}$

D.  ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}$

A

More than 59% of the candidates understood that strong acids have weak conjugate bases.

What is the pH of 0.001 mol dm⁻³ NaOH (aq)?

A. 1

B. 3

C. 11

D. 13

C

The question discriminated well between high scoring and low scoring candidates. 58 % of the candidates were able to calculate the pH of the aqueous solution of NaOH. The most commonly chosen distractor was B (pH = 3) where the students determined pOH but did not complete the calculation. It is interesting that these candidates did not seem to notice that NaOH is a base and should have a higher pH.

Which causes acid deposition?

A.  SO₂

B.  SiO₂

C.  SrO

D.  CO₂

A

What are the products of the reaction between sulfuric acid and sodium hydrogen carbonate?

A.     NaSO₄ + H₂O + CO₂

B.     Na₂SO₄ + CO₂

C.     Na₂SO₄ + H₂O + CO₂

D.     NaSO₄ + H₂CO₃

C

What is the strongest acid in the equation below?

H₃AsO₄ + H₂O $\rightleftharpoons$ H₂AsO₄⁻ + H₃O⁺      K_c = 4.5 × 10⁻⁴

A.  H₃AsO₄

B.  H₂O

C.  H₂AsO₄⁻

D.  H₃O⁺

D

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.

Which of the following is correct?

A.     A weak acid is a proton donor and its aqueous solution shows good conductivity.

B.     A weak acid is a proton donor and its aqueous solution shows poor conductivity.

C.     A weak acid is a proton acceptor and its aqueous solution shows good conductivity.

D.     A weak acid is a proton acceptor and its aqueous solution shows poor conductivity.

B

Which is an example of an amphiprotic species?

A.  Al₂O₃

B.  CO₃²⁻

C.  P₄O₁₀

D.  HPO₄²⁻

D

Which substance will not produce copper(II) chloride when added to dilute hydrochloric acid?

A.  $\mathrm{Cu} \left(\mathrm{s}\right)$

B.  $\mathrm{Cu}\left(\mathrm{OH}{)}_2 \right(\mathrm{s})$

C.  ${\mathrm{CuCO}}_3 \left(\mathrm{s}\right)$

D.  $\mathrm{CuO} \left(\mathrm{s}\right)$

A

Poorly answered with less than ½ of candidates able to identify that copper metal would not produce
copper II chloride when added to dilute HCl.

Which is an acid-base conjugate pair?

A.     H₃O⁺ / OH^–

B.     H₂SO₄ / SO₄^2–

C.     CH₃COOH / H₃O⁺

D.     CH₃NH₃⁺ / CH₃NH₂

D

What is the difference between a conjugate Brønsted–Lowry acid–base pair?

A.  Electron pair

B.  Positive charge

C.  Proton

D.  Hydrogen atom

C

Which of the 0.001 mol dm⁻³ solutions is most likely to have a pH of 11.3?

A.  Ca(OH)₂(aq)

B.  H₃PO₄(aq)

C.  NaOH (aq)

D.  NH₄OH (aq)

A

This required calculation of pH of a base – not an easy task for SL candidates without a calculator. 28% of the candidates answered the question correctly.

Which ions are present in an aqueous solution of Na₂CO₃?

I.   HCO₃⁻
II.  OH⁻
III. CO₃²⁻

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

D

Which statement is incorrect for a 0.10 mol dm^–3 HCOOH solution?

A. pH = 1

B. [H⁺] << 0.10 mol dm^–3

C. [HCOO^–] is approximately equal to [H⁺]

D. HCOOH is partially ionized

A

10.0 cm³ of an aqueous solution of sodium hydroxide of pH = 10 is mixed with 990.0 cm³ of distilled water. What is the pH of the resulting solution?

A. 8

B. 9

C. 11

D. 12

A

Which species behave as Brønsted–Lowry bases in the following reaction? 

H₂SO₄ + HNO₃  H₂NO₃⁺ + HSO₄^- 

A. HNO₃ and HSO₄^- 

B. HNO₃ and H₂NO₃⁺ 

C. H₂SO₄ and HSO₄^- 

D. H₂NO₃⁺ and HSO₄^-

A

Which solution has a pH of 9?

A.  1.0 × 10⁻⁹ mol dm⁻³ $\text{HCl}$ (aq)

B.  1.0 × 10⁻⁵ mol dm⁻³ $\text{KOH}$ (aq)

C.  1.0 × 10⁻⁹ mol dm⁻³ $\text{KOH}$ (aq)

D.  1.0 × 10⁻⁵ mol dm⁻³ $\text{HCl}$ (aq)

B

Which 1.0 mol$$dm^–3 solution has the highest pH?

A.     Ammonium chloride

B.     Sulfuric acid

C.     Sodium chloride

D.     Ammonia

D