(a) (i) Define standard electrode potential. (ii) State two factors that affect the value of standard electrode potential. (iii) Give two uses of the values...

Assessment: WAEC SSCE - Chemistry - 2012 (Essay) Subject: Chemistry

Question 1 Report

 (a) (i) Define standard electrode potential.

(ii) State two factors that affect the value of standard electrode potential.

(iii) Give two uses of the values of standard electrode potential.

(iv) Draw and label a diagram for an electrochemic cell made up of Cu\(^{2+}\)/Cu; E° = +0.34 V  Zn\(^{2+}\)/Zn; E° = -0.76 V

(v) Calculate the e.m.f. of the cell in (a)(iv) above.

(b) (i) In terms of electron transfer, define: I. oxidation; II. oxidizing agent.

(ii) Balance the following redox reaction: MnO\(^{-4}\) + l\(^{-}\) \(\to\) l\(_{2}\) + Mn\(^{2+}\)

(c) Classiify each of the following oxides as basic, amphoteric, acidic or neutral: (i) Carbon (II) oxide; (ii) Sulphu (IV) oxide; (iii) Aluminium oxide; (iv) Lithium oxide.

(d) What is hydrogen bonding?

Answer Details

(a)(i) The standard electrode potential, E°, is the potential of a half-cell measured relative to the standard hydrogen electrode under standard conditions: temperature 298 K, ion concentration 1.0 mol dm−3, and gas pressure 1 atm.

(ii) Two factors which affect electrode potential are:

  1. concentration of ions in the electrolyte;
  2. temperature.

(iii) Standard electrode potentials are used to:

  1. predict the direction or feasibility of a redox reaction;
  2. calculate the e.m.f. of an electrochemical cell.

(iv) A correctly labelled electrochemical cell is shown below.

figure
Labelled Zn|Zn²⁺||Cu²⁺|Cu electrochemical cell.

Cell notation: \[\text{Zn(s)}\;|\;\text{Zn}^{2+}\text{(aq, 1 mol dm}^{-3}\text{)}\;||\;\text{Cu}^{2+}\text{(aq, 1 mol dm}^{-3}\text{)}\;|\;\text{Cu(s)}\] Zinc is the anode (negative electrode) where oxidation occurs, while copper is the cathode (positive electrode) where reduction occurs.

(v)

\[\begin{aligned}E^\circ_{\text{cell}}&=E^\circ_{\text{cathode}}-E^\circ_{\text{anode}}\\&=+0.34-(-0.76)\\&=+1.10\ \text{V}\end{aligned}\]

(b)(i)

  1. Oxidation is the loss of electrons.
  2. An oxidizing agent is a substance that accepts electrons and causes another substance to be oxidized.

(ii) In acidic solution, the balanced ionic equation is:

\[2\text{MnO}_4^-+16\text{H}^++10\text{I}^-\rightarrow2\text{Mn}^{2+}+5\text{I}_2+8\text{H}_2\text{O}\]

(c)

OxideClassification
Carbon(II) oxide, CONeutral
Sulphur(IV) oxide, SO2Acidic
Aluminium oxide, Al2O3Amphoteric
Lithium oxide, Li2OBasic

(d) Hydrogen bonding is the strong intermolecular attraction between a hydrogen atom covalently bonded to nitrogen, oxygen, or fluorine in one molecule and a lone pair of electrons on nitrogen, oxygen, or fluorine in a neighbouring molecule.

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