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 Form 4 Chemistry online video lessons on metals

Chemical and physical properties of zinc

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Answer Text:
Properties of zinc
Physical properties
- Is a blue-grey lustrous metal with:
-Density of 7.1gcm-3
-Melting point of 420oC
-Boiling point of 907oC
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)+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 sulphur
Zn(s)+S(s)2ZnS(s)


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