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Chemistry > Nitric Acid > Flashcards

Nitric Acid Flashcards

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1
Q

what was nitric acid also known as

A

aqua fortis

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2
Q

define fixation of atmospheric nitrogen

A

the conversion of free atmospheric nitrogen into useful nitrgenous compounds in the soil

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3
Q

lab prep of nitric acid

A

potassium nitrate/ sodium nitrate with concentrated sulphuric acid

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4
Q

collection of nitric acid in lab prep

A

the acid vapours condense and are collected in water-cooled receiver ‘Y’

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5
Q

precautions of lab prep of nitric acid

A
  1. apparatus made of glass since acid vapours are corrosive
  2. HCl is not used since it being volatile, cannot displace another volatile acid
  3. temperature is maintained and controlled(apparatus damage, decomposition of nitric acid)
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6
Q

why is sulphuric acid used in lab prep of nitric acid

A

it is a strong non volatile acid, and can displace more volatile nitric acid from the salt

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7
Q

why is the molar ratio of reactants 1:1

A

even though sulphuric acid is dibasic in nature, only half of it is used in formation of acidic salt

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8
Q

why is temp above 200 degrees not used

A
  1. damage to glass
  2. decomposition of nitric acid
  3. formation of hard residual crust of corresponding sulphate
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9
Q

why is nitric acid from lab prep yellowish brown

A

due to decomposition of the acid. decomposition leads to formation of NO2, a reddish brown gas, which imparts colour to the acid

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10
Q

3 chambers of ostwald’s process

A
  1. catalytic chamber
  2. oxidation chamber
  3. absorption tower
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11
Q

ratio of reactants in catalytic chamber, ostwald’s process

A

ammonia: air is 1:10

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12
Q

products of ostwald’s process catalytic chamber

A

nitrogen oxide, steam, 21.5 K heat

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13
Q

temp of oxidation chamber, ostwald’s process

A

50 degrees

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14
Q

what happens in absorption tower of ostwald’s process

A

nitrogen dioxide is converted to nitric acid by absorption in water in the presence of excess air

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15
Q

why is higher ratio of air used in ostwald’s process

A
  1. air is used in all three main reactions
  2. only 21% of air is oxygen
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16
Q

why is heating done initially only in ostwald’s process

A

the reaction is exothermic. the heat evolved maintains the temperature of the reaction

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17
Q

why are low temperatures used in oxidation chamber

A
  1. facilitate easy oxidation of nitric oxide to dioxide
  2. minimise chances of decomposition of NO2
18
Q

why is quartz packed in layers in absorption tower

A
  1. quartz is acid resistant
  2. it is packed in layers since it slows down the movement of gas NO2 and initiates better solvation of nitrogen dioxide in water
19
Q

bp of nitric acid

A

86 C

20
Q

how to make dil. nitric acid concentrated

A
  1. by distilling or boiling until constant boiling mixture is formed
  2. further distilling with conc. sulphuric acid under reduced pressure forms fuming nitric acid
21
Q

odour of nitric acid

A

suffocating

22
Q

density of pure acid

A

1.54

23
Q

density of commercial acid

A

1.42

24
Q

at what temp does nitric acid form constant boiling mixture

A

121 C of water with 68% of acid

25
Q

freezing point of acid

A

-42 C

26
Q

how does nitric acid affect skin

A

reacts with protein in skin forming xanthophenic acid, and stains the skin yellow

27
Q

why can’t distillation be used to concentrate nitric acid

A

on boiling, the mixture evolves out the vapours of both acid and water in same proportion as the liquid

28
Q

how can nitric acid be further concentrated

A

distillation of acid under reduced pressure in the presence of conc. sulphuric acid

29
Q

what is fuming nitric acid

A

98% acid

30
Q

how can colour of acid- formed by NO2- be removed

A

by warming the acid to 60-80 degrees and bubbling air through it

31
Q

ionisation of dilute nitric acid

A

completely ionised intro hydrogen and nitrate ions (monobasic acid)

32
Q

ionisation of concentrated nitric acid

A

poorly ionised
oxidising properties predominate

33
Q

why is hydrogen not released when dilute nitric acid reacts with metals

A
  1. nitric acid on decomposition forms nascent oxygen, which oxidises hydrogen to water
  2. only Mg and Mn react with cold, dilute acid at low temps to release hydrogen
34
Q

what is passivity

A

passivity is exhibited by certain metals under conditions in which chemical activity is expected. (inertness)

35
Q

examples of passivity

A

iron and aluminium are rendered passive when thin oxide coating is formed on the surface

36
Q

define nitration

A

organic compounds in which one or more hydrogen atoms are replaced by a nitro group (NO2), like toluene and benzene

37
Q

tests for nitric acid

A
  1. conc. nitric acid decomposes to form H2O, NO2, O2
  2. copper and conc. nitric acid gives reddish brown fumes of NO2, and blue solution of copper nitrate remains
38
Q

what is aim of brown ring test

A

to detect presence of nitrate (NO3) radical

39
Q

why is freshly prepared iron 2 sulphate soln used in test

A

iron 2 sulphate on exposure to atmosphere is oxidised to iron 3 sulphate, which does not answer to test

40
Q

why is brown ring formed in brown ring test

A

conc. sulphuric acid being heavier, settles down and the iron 2 sulphate layer remains above it resulting in formation of ring at junction

41
Q

why does the brown ring disappear when test tube is shaken in brown ring test

A

the conc. sulphuric acid reacts with water. it is an exothermic reaction, so it decomposes the brown ring

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