Give reasons for each of the following :
(i) Solution of silver nitrate is kept in coloured bottles
(ii) Properties of water are different from the properties of its constituent elements
(iii) Hydrogen is collected by downward displacement of water
(iv) Use of concentrated sulphuric acid as drying agent
(v) Argon is used to fill light bulbs
Answers
I) The solution of silver nitrate is kept in coloured bottles because in the presence of light silver nitrate decomposes to silver .
II) This is because the properties of all compounds is different from it's constitutents.
III) Hydrogen is collected by downward displacement of water as it is less denser than water.
IV) Concentrated Sulphuric Acid is used as a drying agent because it has a strong affinity for water and thus it absorbs water quickly.
V) Argon gas is used in light bulbs to stop the oxygen in the light bulbs from corroding the hot tungsten filament.
The use of argon in light bulbs prevents the evaporation of the tungsten filaments, which results in increased light bulb life.
The reasons of the above questions are:--
(i)Solutions of silver nitrate are kept in coloured bottles generally black because the fast moving photons present in sunlight can decompose the silver nitrate solution into its constituents and black silver solid is deposited at the surface. Therefore to prevent photo dissociation of silver nitrate it is kept in coloured bottles.
(ii)Water is a compound and a compound has properties different from that of constituent elements as compound has mixture of properties of its constituents atoms. Hence they have different properties as compared to elements. Like oxygen is supporter of combustion whereas water is non supporter of combustion.
(iii)Hydrogen is collected by downward motion as it is less denser than water,hence comes at surface of water if it reacts with air it forms explosive or is carried away as it is a light gas. It is highly reactive and burns with blue flame in air and give water so is not collected by upward motion and air as medium
Hence hydrogen is always collected by its downward motion and water as a medium so is collected by displacement of water by downward motion.
(iv)Concentrated sulphuric acid is used as drying agent as concentrated form of acid is highly reactive in nature and has great affinity towards water and hence absorbs water very quickly.
The concentrated form of acid is hygroscopic in nature so absorbs water without dissolving so is good drying , dehydrating or dessicating agent.
(v)Argon is used in light bulbs, fluorescent light so that it can stop the oxygen from corroding the filament of bulb which is made up of tungsten.This increases the life of bulbs as tungsten is protected by argon, in absence of argon tungsten filament would have reacted with oxygen and evaporated.
Argon being noble gas do not react with the filament and is a good coolant so takes the heat produced and hence cool the filament preventing it from busting and thus increases life of bulbs.