Question

give reasons for the following :-
a)keeping food in air tight containers help in preventing rancidity.
b)white colored silver chloride turns grey when exposed to sunlight.
c)metal reacts with non metal is always a redox reaction.
d)corrosion of alumunium is considered to be beneficial.
e)gold and platinum do not get affected by the presence of moist and acidic gases.

Answer 1

a)It does not allow air (oxygen) to come in contact with the food and this prevents oxidation of food. Thus the food never become rancid and its smell and taste remains the same.

b) Silver chloride turns grey due to decomposition reaction. 
This decomposition reaction is called photoletic decomposition. 
2AgCl gives Ag + Cl2 
(silver (silver) (chloride) 
Chloride)

c)redox means -- oxidation and reduction at the same time. there is a new definition for oxidation and reduction. if an atom loses elctrons then it is oxidized and if an atom gains electrons it is reduced. 
so, when a metal and a non metal react, there is an ionic bond formed, which means 1 loses electrons while the other gains them. so, since this reaction involves the exchange of electrons , so it is termed as a redox reaction.

d) When outer layer of aluminium reacts with oxygen it forms a passive layer of aluminium oxide.Though outer layer gets corroded but it creates a protective coating which saves inner layer from further corrosion.Therefore aluminium corrosion becomes advantageous.

e) Gold and platinum are least reactive metals.They do not react with the atmospheric oxygen and water.

Corrosion of some metals like aluminium protect the inner metal.When aluminium corrodes it forms a thin layer of alumium oxide on the surface of the metal.This layer prevents the corrosion of the metal inside.

Answer 2

Answer:

when food is kept in airtight container it slow down the oxidation of food containing fats and oil and therefore prevent rancidity of food