Metal sulphides occur mainly in rocks and metal halides occur in lakes and seas. Give reason.
(b) Pine oil is used in froth flatation process. Why ?
( c) What is a depresent ? Give an example.
(d) What is the role of stabiliser in froth flotation process ?
( e) What is gangue ?

Explanation

(a) Metal halides being soluble in water get dissolved in rain water and are carried to lakes and seas during weathering of rocks. On the other hand, metal sulphides being insoluble are left behind in the rock as residue.
(b) Pine oil increases the non-wetanility of ore particle by water, i.e., ore particles are preferntially wetted by pine oil and hence become ligher and rise to the surface along with the froth.
( c) Depressants are compounds which prevent the formation of froth flotation process. For example, `NaCN` acts as a depressant for `ZnS`in the separation of `ZnS` ore from `PbS` ore.
(d) Chemical compounds namely aniline and cresols. Which tend to stabilise the froth in froth flotating process, are called froth stabilisers.
( e) The earthy and siliceous impurities associated with ores is called gangue.