Medicinal gases, Respiratory mechanism, Oxygen, Nitrogen, Nitrous oxide, Helium, Carbon dioxide, Gasometric assay

1. MEDICINAL GASES
GRACE SHAJI CHITTILAPPILLY
ASSISTANT PROFESSOR
DEPARTMENT OF PHARMACEUTICAL CHEMISTRY
KARPAGAM COLLEGE OF PHARMACY
COIMBATORE-32
Dept. of P Chemistry 1

2. CONTENTS
 INTRODUCTION
 MECHANISM OF INHALATION
 OXYGEN
 CARBON DIOXIDE
 NITROGEN
 NITROUS OXIDE
 HELIUM
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3. INTRODUCTION
oSeveral inorganic gaseous substances find medicinal uses. As they are to be inhaled or
administered through the respiratory system, they may be called inhalants or medicinal gases.
oInhalation happens when air or other gases enter the lungs.
oInhalation of air, as part of the cycle of breathing, is a vital process for all human life.
oThe process is autonomic (though there are exceptions in some disease states) and does not
need conscious control or effort.
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4. MECHANISM OF INHALATION
Inhalation Exhalation
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5. Inhalation begins with the contraction of the muscles attached to the rib cage; this causes an expansion in
the chest cavity.
Then takes place the onset of contraction of the thoracic diaphragm, which results in expansion of the
intrapleural space and an increase in negative pressure according to Boyle’s law.
This negative pressure generates airflow because of the pressure difference between the atmosphere and
alveolus.
The inflow of air into the lungs occurs via the respiratory airways. In health, these airways begin with the
nose.
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6. It is possible to begin with the mouth, which is the backup breathing system. However, chronic mouth
breathing leads to, or is a sign of, illness.
They end in the microscopic dead-end sacs(alveoli) always opened, though the diameters of the various
sections can be changed by the sympathetic and parasympathetic nervous systems.
The alveolar air pressure is therefore always close to atmospheric air pressure (about 100 kPa at sea level)
at rest, with the pressure gradients that cause air to move in and out of the lungs during breathing rarely
exceeding 2–3 kPa.
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7. ◦ Other muscles that can be involved in inhalation include:
• External intercostal muscles
• Scalene muscles
• Sternocleidomastoid muscle
• Trapezius muscle
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8. Dept. of P Chemistry 8

9. OXYGEN (O2)
 Essential to animal and human life.
 Constitutes about 21 % of the atmosphere and 50 % of the terrestrial matter.
 Plants take up CO2 and liberate O2 during photosynthesis
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10. PREPARATION
 Prepared by the fractional distillation of liquid air.
 Prepared by the electrolysis of water.
• Water is a non-conductor of electricity, sodium hydroxide solution is used.
• Iron electrodes are used and oxygen and hydrogen produced are collected separately.
PHYSICAL PROPERTIES
 Colourless
Tasteless
 Odourless
Slightly heavier than air
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11.  Liquefied at -118oC
 Sparingly soluble in water
 Freely soluble in alcohol
CHEMICAL PROPERTIES
 Oxygen stimulate a glowing splinter by burn brightly with a flame.
 Oxygen – most active elements
 At about 5000oC, the molecular form of oxygen (O2) dissociates into the atomic form (O) completely
– More active than molecular form.
 Oxidation reaction of O2 acidified with KMnO4 – gives atomic form (O).
 Oxygen combines with most metal directly.
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12. Magnesium ribbon burns in oxygen forming Magnesium oxide.
OFFICIAL TEST FOR IDENTITY
1. Oxygen causes a glowing splinter to burn brightly.
2. Oxygen is absorbed when shaken with alkaline pyrogallol solution solution turns dark brown.
3. Oxygen is mixed with an equal volume of nitric oxide Red fumes produced.
S + O2
SO2
C + O2 CO2
4Fe + 3O2 2Fe2O3
2Mg + O2 2MgO
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13. TEST FOR PURITY
1. Acidity or alkalinity
2. Carbon monoxide
3. Carbon dioxide
4. Halogens
5. Oxidising substances
Acidity or Alkalinity
• Gas is passed through carbon dioxide-free water containing a specified quantity of 0.01M
hydrochloric acid (Solution 1).
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14. • Another solution containing double the quantity of 0.01M hydrochloric acid is also prepared (Solution
3).
• Finally an equal volume of just carbon dioxide – free water only is also taken (Solution 2).
• Methyl red indicator solution is added to all containers.
• The intensity of colour in solution 1 should be between the colours seen in solutions 2 and 3
indicate that sample of oxygen gas being tested does not contain excess acidity or alkalinity.
Carbon monoxide
Pass the oxygen gas through first anhydrous silical gel impregnated with chromium (VI) oxide (removes
any ammonia and oily matter present in sample)
Pass through conc solution of Pot. Hydroxide (which removes carbon dioxide as Pot. carbonate)
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15. Pass through phosphorous pentoxide dispersed on pumice (removes higher oxides of nitrogen, halogen
and moisture)
Gas then passed into a tube containing heated iodine pentoxide @ 120oC
Oxidizes carbon monoxide to CO2, itself reduced to iodine.
Liberated iodine absorbed in a soln. of KI containing little starch
Titrated against 0.002M sodium thiosulphate
*Blank titration performed with oxygen free air
I2O5 + 5CO I2 + 5CO2
Carbon dioxide
Passing gas through barium hydroxide solution
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16. Turbidity produced , should not be more intense that
Produced by adding prescribed quantity of Sod. Bicarbonate in CO2 free water to barium hydroxide
solution.
Oxidising Substance
Gas is passed through a freshly prepared solution of soluble starch and potassium iodide containing a
little glacial acetic acid.
Colour of liquid not changed
Oxidising substance present
Halogens
Gas is passed through a dilute solution of silver nitrate
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17. No opalescence
Abs of Halogen
STANDARD
 O2 contains not less than 99% v/v of O2
STORAGE
 Storage under compression in appropriate metal cylinders with prescribed safety rules.
 The shoulder of the metal cylinder should be painted white and rest is painted black.
 Name of the gas or symbol ‘O2’ should be on the label and also painted on the shoulder of cylinder.
 Valves should not be lubricated.
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18. MEDICINAL & PHARMACEUTICAL USES
o Medicinal gas
oEssential for breathing
oUsed during surgery
oLiquid oxygen used to remove warts
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19. CARBON DIOXIDE (CO2)
• CO2 present in atmosphere to the extent of about 0.03%
• Produced by combustion, respiration and fermentation reactions.
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20. PREPARATION
1. Prepared by heating alkali carbonates and bicarbonates.
2. Prepared by action of acids on carbonates and bicarbonates.
3. CO2 is also formed from:
• Products of combustion of coke
• Fermentation:
• During the manufacture of lime by burning limestone.
2NaHCO3 Na2CO3 + CO2 + H2O
NaCO3 + H2SO4 Na2SO4 + CO2 + H2O
CaCO3 CaO CO2
+
C6H12O6 2C2H5OH 2CO2
+
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21. PHYSICAL PROPERTIES
 Colourless
 Odourless
 Freely soluble in water
 One and a half times heavier than air.it can be easily liquefied under pressure (50 – 60atm) and this
liquid become solid @ -57.7oC “dry ice”.
CHEMICAL PROPERTIES
CO2 does not support combustion a burning splinter is extinguished when it is introduced into a
jar containing CO2 it dissolves in water to form carbonic acid.
CO2 + H2O H2CO3
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22.  Carbonic acid (dibasic acid) forms both acid and normal salts
 Carbonic acid reddens blue litmus
 CO2 when passed into a soln. of calcium hydroxide (lime water) soln. turns milky due to
formation of calcium carbonate.
On passing more CO2 – liquid become clear due to formation of calcium bicarbonate.
If this soln. heated, CO2 is liberated and soln. again turns milky – due to reprecipitation of calcium
carbonate
NaOH + H2CO3
NaHCO3 + H2O
NaHCO3 + NaOH Na2CO3 H2O
+
Ca(OH)2
CO2 CaCO3 H2O
+ +
CaCO3
H2O CO2 Ca(HCO3)2
+ +
Ca(HCO3)2
CaCO3 H2O CO2
+ +
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23.  CO2 passed through reduced coke, CO2 is reduced to carbon monoxide.
TEST FOR IDENTITY
1. CO2 extinguishes a burning splinter.
2. Gas passed through a solution of barium hydroxide white ppt (Barium carbonate)
dissolves with effervescence on the addition of dil. Acetic acid.
TEST FOR PURITY
Acidity
Phosphoric hydrides, Hydrogen sulphide and organic reducing substances
Carbon monoxide
CO2 C CO
+
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24. Acidity
Pass the gas through carbon dioxide free water containing little methyl orange indicator + 1%w/v of
hydrogen peroxide
Dissolved CO2 flushed out by passing nitrogen for long time
Colour of soln. compared
With another sample of CO2 free water + 1% hydrogen peroxide + methyl orange indicator
To which specified quantity of 0.01M hydrochloric acid added
Phosphoric hydrides, hydrogen sulphide and organic reducing substances
Pass the gas through ammoniacal silver nitrate solution
Soln. compared with original reagent solution through which no gas has been passed
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25. Test solution should not be darker than reagent solution
If dark coloration is seen, it may be due to silver phosphide, silver sulphide or metallic silver
Carbon Monoxide
Pass the CO2 gas through first anhydrous silical gel impregnated with chromium (VI) oxide (removes any
ammonia and oily matter present in sample)
Pass through conc solution of Pot. Hydroxide (which removes carbon dioxide as Pot. carbonate)
Pass through phosphorous pentoxide dispersed on pumice (removes higher oxides of nitrogen, halogen
and moisture)
Gas then passed into a tube containing heated iodine pentoxide @ 120oC
Oxidizes carbon monoxide to CO2, itself reduced to iodine.
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26. Liberated iodine absorbed in a soln. of KI containing little starch
Titrated against 0.002M sodium thiosulphate
*Blank titration performed with CO2 free air
I2O5 + 5CO I2 + 5CO2
STANDARD
 CO2 contains not less than 99 %v/v of CO2
STORAGE
 Kept liquefied under pressure in approved metal cylinders.
 Metal cylinder should be painted grey and carry a label stating carbon dioxide.
 Carbon dioxide or the symbol ‘CO2’ should be stencilled in paint on shoulder of cylinder.
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27. MEDICINAL USE
• Medicinal gas
• Stimulate respiration
• Manufacturing some chemicals.
• Soda water act as carminative and promotes absorption in the stomach.
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28. NITROGEN (N2)
• Atmosphere to the extent of 79%.
• Occur in large quantities as white salt (NaNO3)
• Present as nitrates in the soil formed by soil bacteria such as the nitrifying bacteria.
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29. PREPARATION
 Nitrogen obtained either by removing the oxygen from the atmosphere air or by decomposing
compounds in which it may occur.
 Oxygen may be removed from atmospheric air by any one of following methods:
a. Burning phosphorus in air in a closed container.
b. Passing air over red – hot copper filings
c. Passing air through a soln. of sodium hydrosulphite (Na2S2O4) which will absorb oxygen.
d. Shaking an alkaline solution of pyrogallol with air. Alkaline solution of pyrogallol absorbs oxygen.
 Prepared by fractional distillation of liquid air.
 Chemically, Nitrogen – prepared by oxidation of ammonia with red hot copper oxide.
2NH3 + 3CuO N2 3H2O 3Cu
+ +
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30. PHYSICAL PROPERTIES
Colourless
Odourless
Tasteless
Slightly lighter than air
Slightly soluble in water
Not poisonous but animals die in an atmosphere of nitrogen for lack of oxygen.
Liquefied to a colourless liquid boiling at – 195.8 oC.
N2 neither burns itself nor supports combustion.
Its inert gas
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31. CHEMICAL PROPERTIES
Combines with other elements only with difficulty.
With oxygen it combines only in the presence of lighting or when the mixture is passed through an
electric arc.
With hydrogen it combines under a pressure of 200 – 900 atm & in presence of catalyst made of finely
divided iron and molybdenum @ 452 oC.
Nitrogen – non-combustion and not a supporter of combustion
Burning magnesium or aluminium continues to burn in an atmosphere of nitrogen forming the
corresponding nitride.
N2 O2 2NO
+
N2 + 3H2 2NH3
3Mg N2
Mg3N2
+
Magnesium
nitride
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32. Ash containing the nitride is moistened with water nitride is hydrolysed and ammonia formed can
be tested with red litmus.
TESTS FOR IDENTITY
1. N2 is colourless, odourless and tasteless
2. N2 has no action on litmus and lime water
3. Flame of burning wood splinter introduced into N2 extinguished.
4. Burning magnesium ribbon continues to burn in a jar of nitrogen.
STORAGE
 Stored under pressure in a gas cylinder tightly closed
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33. MEDICINAL USES
o Retard or prevent oxidation by providing inert atmosphere in containers.
o Used for filling electric lamps
o Used in manufacture of ammonia, nitric acid, calcium cyanamide and other nitrogen
compounds.
o Liquid nitrogen used to freeze water
oMercury thermometer used above 200oC have nitrogen filled above the mercury column to
decrease evaporation and to prevent oxidation.
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34. NITROUS OXIDE (N2O)
• Its commonly known as “Laughing gas” because it produces an exhilarating effect
when inhaled.
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35. PREPARATION
 Prepared by heating ammonium nitrate (since ammonium nitrate explode when strongly heated, so
mixture of sodium nitrate and ammonium sulphate may be used).
Gas collected over hot water
Purified by passing through ferrous sulphate soln. (remove higher oxides of nitrogen), caustic soda soln.
(remove nitric acid) and conc. H2SO4 (remove water vapour)
 Formed by reducing nitric acid with stannous chloride and hydrochloric acid
2HNO3 8HCl 4SnCl2
4SnCl4 N2O 5H2O
+ + + +
NH4NO3 N2O 2H2O
+
2NaNO3 + (NH4)2SO4 2N2O 4H2O Na2SO4
+ +
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36. PHYSICAL PROPERTIES
 Colourless
 Odourless
 Tasteless
 One and a half times heavier than air.
 Soluble in water and freely soluble in alcohol.
 Liquefied to a thin, mobile, colourless liquid which boils @ -89.5 oC.
 Liquid freeze to white solid @ -102.4 oC.
CHEMICAL PROPERTIES
 On heating it decomposes into nitrogen and oxygen
2N2O 2N2 O2
+
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37. Does not support combustion.
It readily decomposed, the oxygen released from it supports the combustion of a burning splinter, burning
phosphorous and burning sulphur.
Nitrous oxide is reduced to nitrogen when it is passed over hot copper.
TEST FOR IDENTITY
1. A glowing wood splinter bursts into flame when introduced into the gas.
2. Gas is not absorbed by alkaline pyrogallol solution.
C 2N2O CO2 2N2
+
S 2N2O SO2 2N2
+ +
Cu N2O CuO N2
+ +
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38. TEST FOR PURITY
1. Acidity or alkalinity
2. Arsine and phosphine
3. Carbon dioxide
4. Carbon monoxide
5. Halogens and hydrogen sulphide
6. Nitric oxide and nitrogen dioxide
7. Oxidising substances
8. Water
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39. Acidity and alkalinity – same as in Oxygen
Arsine and Phosphine
 Pass the sample gas through a mercuric chloride paper attached to a glass tube as in limit test for arsenic.
Carbon dioxide
Pass the gas through barium hydroxide soln.
Any turbidity produced
Should not be more intense than that produced by adding specific quantity of sodium bicarbonate in CO2 –
free water to barium hydroxide solution.
Carbon monoxide – same as in Carbon dioxide
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40. Halogens and hydrogen sulphide
Pass the gas through a dilute solution of silver nitrate
Neither opalescence or darkening produced
If opalescence produced If darkness produced
Due to halogens Due to Hydrogen sulphide
Nitric oxide and nitrogen dioxide – limited by spectrophotometric test
First the higher oxides of nitrogen oxidised to nitrous acid which is used to diazotise sulphanilic acid in acetic
acid.
Coupled with N-1(1-naphthyl) ethylenediamine dihydrochloride in acetic acid
Colour obtained is compared with
Colour obtained by adding specified quantity of sodium nitrite to reagent soln. containing
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41. Sulphanilic acid in glacial acetic acid mixed with N- (1-naphthyl) ethylenediamine dihydrochloride.
Red colour in sample soln. should not be more intemse than reference solution.
Oxidising substances
Pass the gas through KI soln. containing starch
No blue colour produced
No oxidizing substance
STANDARD
 Nitrous oxide contains not less than 95% v/v of N2O in gaseous phase.
STORAGE
 Stored under compression in metal cylinders of type conforming to appropriate safety regulations.
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42.  Temp. not exceeding 37oC.
 Cylinder painted blue and carries a label with name of gas or N2O which is painted on shoulder of
cylinder.
MEDICINAL USES
 Medicinal gas
 General anaesthetic
 Analgesic
 Used for calming excited mental patients.
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43. HELIUM (He)
 It is an inert gas.
 It is present in a concentration of 2% in the natural gas obtained from Canada and
U.S.A.
 It is also present in ores of some radioactive elements such as uranium and thorium.
 Helium is always present in the free state.
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44. PREPARATION
 First a mixture of noble or inert gases is isolated from air which should have been already freed from dust,
carbon dioxide, water vapour etc..
For this dry air is passed over heated copper where oxygen in air is removed as copper oxide.
Next air is passed over heated magnesium which removes nitrogen as magnesium nitride.
Theses procedure is repeated again and again till O2 and N2 are completely removed.
Residual air is only mixture of noble gases
Noble gases are separated by using coconut charcoal which adsorbs each gas at a different temp.
Mixture of noble gases is sent into a double-walled glass bulb containing coconut charcoal placed in a bath at
373K and allowed to remain in contact with charcoal for about half an hour. - @ this temp. Argon, Krypton and
xenon are adsorbed
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45. This mixture allowed to remain in contact with another sample of coconut charcoal at 93K only Neon is
absorbed and Helium is left free.
 Helium also obtained by fractionation of the liquid air.
 Obtained from natural petroleum gas by liquefaction and rectification at low temperatures.
 Helium is obtained by heating monazite to 1273K or by heating with dil. H2SO4 or KHSO4.(pass it over
KOH solution to free it from CO2)
PROPERTIES
 Colourless
 Odourless
 Tasteless
 it is the lightest gas after hydrogen.
It is monatomic and can be liquefied under pressure.
If helium is cooled below 2.18K, a new form of He called HeII is obtained. It exhibits unusual
properties and is called as degenerate gas or superfluid.
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46.  Its thermal conductivity is very high.
 It is able to rise against gravity and flow over the top of the container in which it is kept.
TESTS FOR PURITY
 Acidity or alkalinity
 Oxidising substance
 Reducing substance
 Carbonaceous compounds
 Specific gravity
1. Acidity or alkalinity : same as Oxygen.
2. Reducing substance
Pass gas through a dilute solution of KMnO4.
Colour should not be completely discharged.
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47. 3. Carbonaceous compounds
Pass the gas over activated copper oxide heated to 600oC
The pass through barium hydroxide solution
Any carbonaceous compound present is oxidized to CO2 which produces turbidity in Ba(OH)2 solution
Turbidity is matched against a std.
4. Specific gravity: determined by weighing a sample of gas in a glass bulb.
ASSAY
A sample of the gas is introduced into a glass bulb containing coconut charcoal cooled by liquid oxygen.
Unabsorbed gas (Helium) is pumped out and measured.
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48. STORAGE
◦ Helium is kept at a pressure in a metallic cylinder able to withstand the pressure in a cool dry place.
◦ The body and valve end of the gas cylinder should be painted brown.
◦ Cylinder containing O2 and He mixtures should have the body painted black and the value end
painted white and brown.
MEDICINAL USES
◦ Medicinal gas.
◦ Mixture of He (79%) & O2 (21%) is administered in cases of Respiratory distress.
◦ Used for inflating tyres of aeroplanes and for filling balloons (Becoz of its lightness and non-
inflammable).
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49. GASOMETRIC
ASSAY
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50. ASSAY OF NITROUS OXIDE
APPARATUS
 Comprises of a gas burette of 100 ml capacity
 Connected through a two – way tap at its upper end to two capillaries:
Capillary A – used to introduce the gas into the apparatus
Capillary B – being connected to a vertical capillary arm to form a four-way junction
 Descending arm of the junction is connected to a condenser (C) of 60 ml capacity.
 Right arm of junction is connected to a mercury manometer (M).
 Tap D on upper vertical arm of junction opens to the air.
The lower part of gas burette is fitted with a one-way tap connected to a rubber tube to a mercury
reservoir.
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51. The upper part of burette is graduated from 0 to 5 ml and lower part from 99.5 to 100.5 ml, both in
increments of 0.1 ml.
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52. METHOD
 Close the 3 taps and immerse the condenser in liquid nitrogen, keeping the level slightly above the upper
part of the condenser.
 By manipulation 2-way tap and mobile reservoir create a partial vaccum in apparatus, choosing an
arbitrary pressure Po (btw 6.7 and 8 kPa).accurately measured.
 Pressure must remain constant for 10 mins to demonstrate that the apparatus is gas-tight.
 Open the 2-way tap to tube A and completely fill the burette and tube A with mercury.
 Close the 2-way tap.
 Connect a rubber tube through a suitable pressure –relieving device to exit valve of cylinder of gas
under examination and pass a current of gas through the rubber tube for 1 min.
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53.  Whilst the gas is still flowing , connect the rubber tube to end of tube A and immediately open the two
way tap to tube A.
 Allow the specified vol. of gas to enter the burette by lowering the mercury reservoir.
 Disconnect the rubber tube and expel the gas from burette by slowly raising the mercury reservoir above
the capillary tube.
 Allow the specified quantity of gas under examination to enter the burette by lowering the mercury
reservoir and ensure that the pressure of gas is equal to atmospheric pressure.
 Close the 2-way tap.
 Raise the mercury reservoir slightly above tube A and lower the level of liquid nitrogen to the middle of
the condenser.
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54.  Carefully open the tap of the burette to connect with the condenser and allow the mercury to rise in the
burette until it reaches the tap close the tap.
 Raise the level of the liquid nitrogen so as to totally immerse the condenser read the pressure and
wait until it remains steady for 2 mins.
 Place the mercury reservoir in its bottom position and open the tap of the burette to make connection
with the condenser.
 Move the mercury reservoir until the manometer reading is the same as the initial pressure Po.
 Close the tap of the burette and, by means of the mercury reservoir, bring the pressure of the gas in the
burette to atmospheric pressure.
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55.  The number of ml of gas represents the non-condensable volume in the specified volume used.
 After each series of 10 determinations allow atmospheric air to enter by opening the tap D, remove the
liquid nitrogen from the condenser and allow the condenser to warm to room temp.
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56. ASSAY OF OXYGEN
APPARATUS
 Comprises a gas burette as that of assay of nitrous oxide
 Tube B is connected to a gas pipette comprising two bulbs of suitable size.
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57. METHOD
 Charge the pipette with the reagents specified in the monograph. (Ammonia buffer 10.9 solution)
 With the two-way tap open to tube B, draw the solution just to the level of the tap by moving the
mercury reservoir.
 Open the two-way tap to tube A, completely fill the burette and tube A with mercury and close the two-
way tap.
 Connect a rubber tube to the exit valve of the cylinder of the gas under examination through a suitable
pressure reducing device and pass a current of the gas through the tube for 1 mins.
 Whilst the gas is still flowing, connect the rubber tube to tube A, immediately open the two-way tap to
tube A, allow the specified quantity of the gas to enter the burette by lowering the mercury reservoir and
close the two-way tap.
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58.  Increase the pressure of the gas by raising the mercury reservoir, open the two-way tap to tube B and
transfer all the gas to the pipette.
 Close the tap and gently shake the pipette.
 After 15 mins, when most of the gas has been absorbed by the liquid , draw the residual gas back into the
burette and repeat the procedure beginning at the words “ Increase the pressure of the gas..” until the
volume of residual gas is constant.
 Measure the volume of the residual gas in the burette.
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59. THANK YOU….
Dept. of P Chemistry 59
“EVERYDAY IS A CHANCE TO GET BETTER, DON’T WASTE IT…”