4.6 CHAPTER 4. ELECTROCHEMICAL REACTIONS
(b) Consider the reaction represented by the following equation:
Br2(l)+ 2I−aq→ 2Br−aq+ I2(s)
Which one of the following statements about this reaction is cor-
rect?
i. bromine is oxidised
ii. bromine acts as a reducing agent
iii. the iodide ions are oxidised
iv. iodine acts as a reducing agent
(IEB Paper 2, 2002)
(c) The following equations represent two hypothetical half-reactions:
X 2 + 2e−� 2X−(+1.09 V) and
Y++ e−� Y (− 2. 80 V)
Which one of the following substances from these half-reactions
has the greatest tendency to donate electrons?
i. X−
ii. X 2
iii. Y
iv. Y+
(d) Which one of the following redox reactionswill not occur spon-
taneously at room temperature?
i. Mn + Cu2+→ Mn2++ Cu
ii. Zn + SO^24 −+ 4H+→ Zn2++ SO 2 + 2H 2 O
iii. Fe3++ 3NO 2 + 3H 2 O→ Fe + 3NO− 3 + 6H+
iv. 5H 2 S + 2MnO− 4 + 6H+→ 5S + 2Mn2++ 8H 2 O
(e) Which statement isCORRECT for a Zn-Cu galvanic cell that op-
erates under standard conditions?
i. The concentration ofthe Zn2+ions in the zinc half-cellgrad-
ually decreases.
ii. The concentration of the Cu2+ions in the copper half-cell
gradually increases.
iii. Negative ions migrate from the zinc half-cell to the copper
half-cell.
iv. The intensity of thecolour of the electrolytein the copper
half-cell gradually decreases.
(DoE Exemplar Paper 2,2008)
- In order to investigatethe rate at which a reaction proceeds, a learner
places a beaker containing concentrated nitric acid on a sensitive bal-
ance. A few pieces of copper metal are droppedinto the nitric acid.
(a) Use the relevant half-reactions from the table of Standard Reduc-
tion Potentials to derivethe balanced nett ionicequation for the
reaction that takes placein the beaker.
(b) What chemical property of nitric acid is illustrated by this reac-
tion?
(c) List three observations that this learner would make during the
investigation.
