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Chemical and physical properties of zinc

Answer Text:
Properties of zinc
Physical properties
- Is a blue-grey lustrous metal with:
-Density of # 7.1gcm^(-3)#
-Melting point of #420^oC#
-Boiling point of #907^oC#
Chemical reactions
(a). with air;-
- Zinc tarnishes slowly forming a protective layer which prevents further reaction i.e. oxide layer or
basic carbonate.
Equations:
#2Zn(s) + O_2(g) to 2ZnO(s)#
Then;
#ZnO(s) + CO_2(g) to ZnCO_3(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) + O_2(g) to 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) + H_2O(g) to ZnO(s) + H_2(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^(+) to (aq) Zn^(2+) (aq) + H_2(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) + 2H_2SO_4(l) to ZnSO_4(aq) + 2H_2O(l) + SO_2(g)#
(ii). 50% concentrated nitric (v) acid.
- It reacts with 50% concentrated nitric (V) acid to liberate nitrogen (II) oxide.
Equation:
#3Zn(s) + 8HNO_3(l) to Zn(NO_3)_2(aq) + 2H_2O(l) + 2NO(g)#
(iii). Concentrated nitric (V) acid.
- It reduces concentrated nitric (V) acid to nitrogen (IV) oxide.
Equation:
#Zn(s) + 4HNO_3(l) to Zn(NO_3)_2(aq) + 4H_2O(l) + 2NO_2(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) + 2H_2O(l) to H_2(g) + [Zn(OH)_4]^(2-) (aq)# (Zincate ion)
(f). Other reactions.
(i). Zinc burns in chlorine to give zinc chloride #Zn(s) + Cl_2(g) ZnCl_2(s)#
(ii). Zinc combines with sulphur
#Zn(s) + S(s) to 2ZnS(s)#