Chemistry
With respect to the brown ring test for nitrates, explain :
(a) Freshly prepared ferrous sulphate is used.
(b) Brown ring disappear if the test tube is disturbed.
(c) Lead nitrate does not respond properly to the brown ring test.
Hint - Salt solution forming insoluble sulphates interfere with the result of the brown ring test.
(d) What is the name and formula of the brown ring formed ?
Answer
(a) Freshly prepared FeSO4 is used in the brown ring test, because upon exposure to the atmosphere, it is oxidised to ferric sulphate which will not give brown ring.
(b) The brown ring of nitroso ferrous sulphate decomposes on disturbing the test tube. The heat evolved decomposes the unstable brown ring.
(c) Lead nitrate (Pb(NO3)2) contains Pb2+ ions, which can form an insoluble precipitate of PbSO4 when H2SO4 (sulphuric acid) is added.
This precipitate interferes with the formation of the necessary layers and prevents proper diffusion and interaction with Fe2+, thus suppressing the brown ring formation.
(d) Nitroso ferrous sulphate - FeSO4.NO
Related Questions
(a) Mention three important uses of nitric acid. Give the property of nitric acid involved in the use.
(b) Explain with the help of a balanced equation, the brown ring test for nitric acid.
(c) Why is freshly prepared ferrous sulphate solution used for testing the nitrate radical in the brown ring test
The action of heat on the blue crystalline solid X, gives a reddish brown gas Y, a gas which re-lights a glowing splint and leaves a black residue. When gas Z, which has a rotten egg smell, is passed through a solution of X, a black ppt. is formed.
(a) Identify X, Y and Z.
(b) Write equation for action of heat on X.
(c) Write equation between solution of X and gas Z.
(a) Dilute nitric acid is generally considered a typical acid except for it's reaction with metals. In what way is dilute nitric acid different from other acids when it reacts with metals?
(b) Write the equation for the reaction of dilute nitric acid and conc. nitric acid with copper.
The figure given below illustrates the apparatus used in the laboratory preparation of nitric acid.
(a) Name A (a liquid), B (a solid) and C (a liquid). (Do not give the formulae).
(b) Write an equation to show how nitric acid undergoes decomposition.
(c) Write the equation for the reaction in which copper is oxidized by concentrated nitric acid.