Chemical and physical properties of zinc
Answer Text: Properties of zincPhysical properties- Is a blue-grey lustrous metal with:-Density of 7.1gcm-3-Melting point of 420oC-Boiling point of 907oCChemical reactions(a). with air;-- Zinc tarnishes slowly forming a protective layer which prevents further reaction i.e. oxide layer orbasic carbonate.Equations:2Zn(s)+O2(g)→2ZnO(s)Then;ZnO(s)+CO2(g)→ZnCO3(s)- It burns with a blue-green flame when strongly heated in air to form an oxide which is yellow when hot and white when cold.Equation:2Zn(s)+O2(g)→2ZnO(s)(b). With water- Zinc does not react with water- Steam reacts with red-hot zinc, forming zinc oxide and liberating hydrogen gas.Equation:Zn(s)+H2O(g)→ZnO(s)+H2(g)(c). with dilute acids- Zinc is above hydrogen in the reactivity series hence displaces hydrogen from steam (water) and dilute acids like H2SO4 and HCl.Equation:Zn(s)+2H+→(aq)Zn2+(aq)+H2(g)- Pure zinc reacts slowly while impure zinc reacts faster/ more quickly.- Copper (II) sulphate is used as a catalyst to speed up the reaction.(d). Concentrated acids.(i). Concentrated sulphuric (VI) acid.Equation:Zn(s)+2H2SO4(l)→ZnSO4(aq)+2H2O(l)+SO2(g)(ii). 50% concentrated nitric (v) acid.- It reacts with 50% concentrated nitric (V) acid to liberate nitrogen (II) oxide.Equation:3Zn(s)+8HNO3(l)→Zn(NO3)2(aq)+2H2O(l)+2NO(g)(iii). Concentrated nitric (V) acid.- It reduces concentrated nitric (V) acid to nitrogen (IV) oxide.Equation:Zn(s)+4HNO3(l)→Zn(NO3)2(aq)+4H2O(l)+2NO2(g)(e). with alkalis.- Zinc is amphoteric and dissolves in hot alkalis to give the zincate ion and hydrogen gas.Equation:Zn(s)+2OH-(aq)+2H2O(l)→H2(g)+[Zn(OH)4]2-(aq) (Zincate ion)(f). Other reactions.(i). Zinc burns in chlorine to give zinc chloride Zn(s)+Cl2(g)ZnCl2(s)(ii). Zinc combines with sulphurZn(s)+S(s)→2ZnS(s)