(a) Explain the statement, the standard electrode potential of zinc is -0.76 v.What is meant by the term periodic property of elements? (b) Consider the fol...
Question 1 Report
(a) Explain the statement, the standard electrode potential of zinc is -0.76 v.What is meant by the term periodic property of elements?
(b) Consider the following standard electrode potentials:
| \( \mathrm{Zn}^{2+}_{(aq)} + 2e^- \) | \( \mathrm{Zn(s)} \) | Eᶿ = - 0.76 V |
| \( \mathrm{Cu}^{2+}_{(aq)} + 2e^- \) | \( \mathrm{Cu(s)} \) | Eᶿ = + 0.34 V |
When the two half cells are connected:
(i) write the reaction equation at each electrode;
(ii) write the overall cell reaction equation;
(iii) state the type of reaction occurring at each electrode;
(iv) calculate the e.m.f. of the cell.
(c) (i) Name two chemical industries.
(ii) State two factors that should be considered when siting a chemical industry.
(iii) List two effects of a chemical industry on the community in which it is sited.
(d) Using chemical equations, explain briefly what would happen when hydrogen peroxide is added to:
(i) silver oxide;
(ii) chlorine gas.
(e) List three physical properties of nitrogen.
Answer Details
(a) The statement means that when a zinc electrode dipped in a 1 mol dm-3 solution of its ions at 25 °C is connected to a standard hydrogen electrode, the measured potential difference is 0.76 V, with zinc as the negative electrode. Zinc therefore loses electrons more readily than hydrogen (it is a stronger reducing agent).
A periodic property is a property (e.g. atomic radius, ionization energy, electronegativity) that varies regularly and recurs at intervals with increasing atomic number of the elements.
(b)(i) Anode (Zn): \( \text{Zn} \to \text{Zn}^{2+} + 2e^- \)
Cathode (Cu): \( \text{Cu}^{2+} + 2e^- \to \text{Cu} \)
(b)(ii) \[ \text{Zn} + \text{Cu}^{2+} \to \text{Zn}^{2+} + \text{Cu} \]
(b)(iii) Oxidation at the zinc electrode; reduction at the copper electrode.
(b)(iv) \[ E_{cell} = E_{cathode} - E_{anode} = (+0.34) - (-0.76) = +1.10\ \text{V} \]
(c)(i) The petrochemical industry and the fertilizer industry.
(c)(ii) Nearness to raw materials and availability of water and power.
(c)(iii) Provision of employment/development (beneficial) and environmental pollution of air and water (harmful).
(d)(i) Hydrogen peroxide reduces silver oxide, liberating oxygen:
\[ \text{Ag}_2\text{O} + \text{H}_2\text{O}_2 \to 2\text{Ag} + \text{H}_2\text{O} + \text{O}_2 \]
(d)(ii) Hydrogen peroxide reduces chlorine:
\[ \text{H}_2\text{O}_2 + \text{Cl}_2 \to 2\text{HCl} + \text{O}_2 \]
(e) Nitrogen is a colourless, odourless, tasteless gas; it is slightly (sparingly) soluble in water; and it is slightly less dense than air (and neutral to litmus).
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