(a) (i) Consider the following metals:

K, Ca, Al, Cu, Ag, Fe

Select from the above metals, a metal which

I. does not react with oxygen even at high temperature.

II. reacts with oxygen at ordinary temperature and forms a protective oxide layer which prevents the metal from further oxidation.

III. catches fire when kept in the open.

IV. does not burn in oxygen but the hot metal is coated with a black coloured oxide layer.

(ii) What are amphoteric oxides? With the help of balanced chemical equations show that aluminium oxide is an amphoteric oxide.

(iii) What are alkalis? Give one example.

OR

(b) (i) With the help of balanced chemical equations state the process of extracting (I) mercury from its ore called cinnabar, and (II) copper from its sulphide ore.

(ii) Silver and copper articles slowly lose their shiny surfaces when exposed to air. Name the compounds formed on (I) silver articles, and (II) copper articles in the form of coating.

(a) (i) I. Silver (Ag) does not react with oxygen even at high temperature.

II. Aluminium (Al) reacts with oxygen at ordinary temperature and forms a protective oxide layer which prevents the metal from further oxidation.

III. Potassium (K) catches fire when kept in the open.

IV. Copper (Cu) does not burn in oxygen but the hot metal is coated with a black coloured oxide layer.

(ii) Amphoteric oxides are those oxides which react with both acids as well as bases to produce salts and water. Aluminium oxide is an amphoteric oxide. It reacts with both acids as well as bases to produce salts and water.

Al2O3 + 6HCl $\rightarrow$ 2AlCl3 + 3H2O

Al2O3 + 2NaOH $\rightarrow$ 2NaAlO2 + H2O

(iii) Alkalis are the hydroxides of highly electropositive metals. One example of an alkali is sodium hydroxide (NaOH).

OR

(b) (i) (I) The process of extracting mercury from its ore called cinnabar is: 2HgS + 3O2 $\rightarrow$ 2HgO + 2SO2

HgO + H2 $\rightarrow$ Hg + H2O

(II) The process of extracting copper from its sulphide ore is: 2Cu2S + 3O2 $\rightarrow$ 2Cu2O + 2SO2

Cu2O + FeS $\rightarrow$ Cu2S + FeO

(ii) (I) The compound formed on silver articles is silver sulphide (Ag2S).

(II) The compound formed on copper articles is copper oxide (CuO).