(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:
Zn\(^{2+}\)\(_{(aq)}\) + 2e\(^-\) Zn(s) EαΆΏ = – 0.76 V
Cu\({2+}\)\(_{(aq)}\) + 2e\(^-\) Cu(s) EαΆΏ = + 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.
Explanation
(a) When a standard hydrogen electrode is connected to a standard zinc half-cell the emf measured is 0.76V. The negative sign implies the flow of electrons from the zinc electrode to the hydrogen electrode.
(b)(i) Anode/ Zn electrode
Zn(s) β Zn\(^{2+}\)\(_{(aq)}\) + 2e\(^-\) / Zn(s) β 2e\(^-\) β Zn\(^{2+}\)\(_{(aq)}\)
Cathode/Cu electrode
Cu\(^{2+}\) \(_{(aq)}\) + 2e\(^-\) β Cu(s)
(ii) Zn(s) + Cu\(^{2+}_{(aq)}\) β Zn\(^{2+}_{(aq)}\) + Cu(s)
(iii) Anode/Zn electrode β oxidation
Cathode/Cu electrode β reduction
(iv) Eocell = Eored β Eooxid
= (0.34 V) β (-0.76 V)
= + 1.10 V
(c) (i) - Textile
- Brewery
- Plastic
- Refinery
- Cement
- Food [e.g flour, tea, sugar, etc]
- Pharmaceutical
- Fertilizer
- Metallurgical
- Paint
- Soap and detergent
- Ceramic
- Rubber
- Glass
- Etc
(ii) - nearness to raw materials / feed stock
- nearness to market
- labour supply
- transportation
- nearness to power supply
- government policy
- away from residential area
- availability of water
(iii)- Improvement in the standard of living
- Employment opportunities
- Development in the community
- Pollution: air, noise, water, thermal
- Social effects
(d)(i) Hydrogen peroxide reduces silver oxide to silver metal/H2O2is oxidized to O2
A + H\(_2\)O\(_2\)\(_{(aq)}\) β 2Ag\(_{(s)}\) + H\(_2\)O\(_{(l)}\) + O\(_{2(g)}\)
(ii) Hydrogen peroxide reduces chlorine to hydrochloric acid/H\(_2\)O\(_2\) is oxidized to O\(_2\)
Cl\(_{2(g)}\) + H\(_2\)O\(_{2(aq)}\) β 2HCl\(_{(aq)}\) + O\(_{2(g)}\)
(e) - colourless
- odourless
- slightly lighter / less dense than air
- slightly soluble in water
- low melting (-210\(^{o}\)C/ 63 K)/low boiling point (-196\(^{o}\)C/ 77 K)