Chemistry
Explain why
(a) Only all-glass apparatus should be used for the preparation of nitric acid by heating concentrated sulphuric acid and potassium nitrate.
(b) Nitric acid is kept in a reagent bottle for a long time.
Answer
(a) All glass apparatus is used in the laboratory preparation of nitric acid since the vapours of nitric acid being highly corrosive attack rubber, cork, etc.
(b) When nitric acid is kept in a reagent bottle for a long time, it turns dark yellowish brown in colour.
This is because nitric acid is unstable hence, it decomposes slightly even at ordinary temperatures and in the presence of sunlight. When it is kept for a long time, the decomposition is complete resulting in the formation of reddish brown nitrogen dioxide [NO2] that dissolves in the acid giving it a darker yellowish brown colour.
4HNO3 ⟶ O2 + 2H2O + 2NO2
Related Questions
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.
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 ?