Nitric Acid Flashcards
what was nitric acid also known as
aqua fortis
define fixation of atmospheric nitrogen
the conversion of free atmospheric nitrogen into useful nitrgenous compounds in the soil
lab prep of nitric acid
potassium nitrate/ sodium nitrate with concentrated sulphuric acid
collection of nitric acid in lab prep
the acid vapours condense and are collected in water-cooled receiver ‘Y’
precautions of lab prep of nitric acid
- apparatus made of glass since acid vapours are corrosive
- HCl is not used since it being volatile, cannot displace another volatile acid
- temperature is maintained and controlled(apparatus damage, decomposition of nitric acid)
why is sulphuric acid used in lab prep of nitric acid
it is a strong non volatile acid, and can displace more volatile nitric acid from the salt
why is the molar ratio of reactants 1:1
even though sulphuric acid is dibasic in nature, only half of it is used in formation of acidic salt
why is temp above 200 degrees not used
- damage to glass
- decomposition of nitric acid
- formation of hard residual crust of corresponding sulphate
why is nitric acid from lab prep yellowish brown
due to decomposition of the acid. decomposition leads to formation of NO2, a reddish brown gas, which imparts colour to the acid
3 chambers of ostwald’s process
- catalytic chamber
- oxidation chamber
- absorption tower
ratio of reactants in catalytic chamber, ostwald’s process
ammonia: air is 1:10
products of ostwald’s process catalytic chamber
nitrogen oxide, steam, 21.5 K heat
temp of oxidation chamber, ostwald’s process
50 degrees
what happens in absorption tower of ostwald’s process
nitrogen dioxide is converted to nitric acid by absorption in water in the presence of excess air
why is higher ratio of air used in ostwald’s process
- air is used in all three main reactions
- only 21% of air is oxygen
why is heating done initially only in ostwald’s process
the reaction is exothermic. the heat evolved maintains the temperature of the reaction
why are low temperatures used in oxidation chamber
- facilitate easy oxidation of nitric oxide to dioxide
- minimise chances of decomposition of NO2
why is quartz packed in layers in absorption tower
- quartz is acid resistant
- it is packed in layers since it slows down the movement of gas NO2 and initiates better solvation of nitrogen dioxide in water
bp of nitric acid
86 C
how to make dil. nitric acid concentrated
- by distilling or boiling until constant boiling mixture is formed
- further distilling with conc. sulphuric acid under reduced pressure forms fuming nitric acid
odour of nitric acid
suffocating
density of pure acid
1.54
density of commercial acid
1.42
at what temp does nitric acid form constant boiling mixture
121 C of water with 68% of acid
freezing point of acid
-42 C
how does nitric acid affect skin
reacts with protein in skin forming xanthoproteic acid, and stains the skin yellow
why can’t distillation be used to concentrate nitric acid
on boiling, the mixture evolves out the vapours of both acid and water in same proportion as the liquid
how can nitric acid be further concentrated
distillation of acid under reduced pressure in the presence of conc. sulphuric acid
what is fuming nitric acid
98% acid
how can colour of acid- formed by NO2- be removed
by warming the acid to 60-80 degrees and bubbling air through it
ionisation of dilute nitric acid
completely ionised intro hydrogen and nitrate ions (monobasic acid)
ionisation of concentrated nitric acid
poorly ionised
oxidising properties predominate
why is hydrogen not released when dilute nitric acid reacts with metals
- nitric acid on decomposition forms nascent oxygen, which oxidises hydrogen to water
- only Mg and Mn react with cold, dilute acid at low temps to release hydrogen
what is passivity
passivity is exhibited by certain metals under conditions in which chemical activity is expected. (inertness)
examples of passivity
iron and aluminium are rendered passive when thin oxide coating is formed on the surface
define nitration
organic compounds in which one or more hydrogen atoms are replaced by a nitro group (NO2), like toluene and benzene
tests for nitric acid
- conc. nitric acid decomposes to form H2O, NO2, O2
- copper and conc. nitric acid gives reddish brown fumes of NO2, and blue solution of copper nitrate remains
what is aim of brown ring test
to detect presence of nitrate (NO3) radical
why is freshly prepared iron 2 sulphate soln used in test
iron 2 sulphate on exposure to atmosphere is oxidised to iron 3 sulphate, which does not answer to test
why is brown ring formed in brown ring test
conc. sulphuric acid being heavier, settles down and the iron 2 sulphate layer remains above it resulting in formation of ring at junction
why does the brown ring disappear when test tube is shaken in brown ring test
the conc. sulphuric acid reacts with water. it is an exothermic reaction, so it decomposes the brown ring
