Laboratory preparation

1. Virtual Class
Topic: Lab Preparation
Class-XI
By
DP Paneru
M.Sc Chemistry
d.ppaneru1991@gmail.com

2. S.N. Content
1 Laboratory preparation Carbon Monoxide
2 Laboratory preparation of HI
3 Laboratory Preparation of hydrogen gas
4 Laboratory Preparation of hydrogen sulphide gas
5 Preparation of H2S by Kipp's Apparatus
6 Laboratory Preparation of SO2 gas
7 Laboratory Preparation of Ethene
8 Laboratory Preparation of Ethyne

3. Lab Preparation of CO
Carbon monoxide was first prepared in the laboratory in 1776 by J.M.F. de Lassone,
a French chemist. As carbon monoxide is extremely poisonous, its preparation
should be carried out only in a fume chamber.
In the laboratory carbon monoxide is prepared oxalic acid crystals with conc. H2SO4.
COOH ∆
│ + conc. H2SO4 → CO2 + CO + ( H2SO4.H2O)
COOH

4. Conc. H2SO4 dehydrates oxalic acid crystals and a mixture of CO2 and CO is set
free. The oxalic acid crystals are taken in a round bottomed flask and conc.
H2SO4 poured into it. On heating, mixture of gases (CO2 and CO) is produced
which is passed through sodium hydroxide where CO2 is absorbed by it and CO
is obtained.
CO is collected in the gas jar by downward displacement of water.
Physical Properties
a)Carbon monoxide is colorless, almost odorless and tasteless gas.
b) It is very slightly lighter than air.
c)Carbon monoxide is only very slightly soluble in water.
d) It is poisonous gas. Air containing even less than 1% of carbon monoxide, can be
fatal, if breathed in for about 10 to 15 minutes.

5. Chemical properties
 It is neutral (neither acidic nor basic in nature).
It doesn’t support combustion but burns with blue flame & gives carbon dioxide.
2CO + O2⟶2CO2 + Heat
 It reacts with hydrogen to form methanol (CH3 -OH).
CO + 2H2⟶CH3−OH
 It reacts with chlorine to form phosgene (phosgene can be used as deadly
weapon)
CO + Cl2⟶COCl2
 It reacts with caustic soda (NaOH) to form sodium formate (HCOONa).
CO + NaOH⟶HCOONa
 It combines with metals like iron, nickel, cobalt to form carbonyls.
Fe + 5CO⟶Fe(CO)5(Iron carbonyl)
Ni + 4CO⟶Ni(CO)4(Nickel carbonyl)
Co + 4CO⟶Co(CO)4(Cobalt carbonyl)
 It reacts as the reductant. It reduces metals oxides into metal.
Fe2O3 + 3CO⟶2Fe + 3CO2 (Ferric oxide to iron)
ZnO + CO⟶Zn + CO2 (Zinc oxide to zinc)

6. Uses
 Used as fuel.
 Used to prepare weapon ie. Phosgene.
 Purification of nickel by Mond’s process is done with it’s application.

7. Laboratory preparation of HI
In the laboratory, HI is prepared by dropping water on a mixture of red phosphorus
and iodine. A mixture of iodine and red phosphorus is taken in the flask and water
is dropped from the funnel. HI with some vapour of iodine is evolved.
P4 + 6I2 → 4PI3
PI3 + 3H2O → 3HI + H3PO3 ] * 4
P4 + 6I2 + 12H2O → 12HI + 4H3PO3
HI cannot be prepared in the same way as HCl by using conc. H2SO4 because HI
being stronger reducing agent, reduces the oxidizing acid (i.e.conc. H2SO4) to
SO2.
2HI + H2SO4 → SO2 + 2H2O + I2

8. Physical Properties
Hydrogen iodide is a colorless gas, with an acrid odor.
It is exceptionally soluble in water (245 g/100 mL), giving hydroiodic acid.
The dissolution is exothermic.
It is also slightly soluble in alcohols.

9. Laboratory Preparation of hydrogen gas
Principle
Hydrogen gas is prepared in laboratory by reacting dilute H2SO4.
Zn + dil. H2SO4 → ZnSO4 + H2 ↑
It is a redox reaction in which hydrogen is reduced and zinc is oxidized.

10. Procedure
The apparatus is shown in the figure. To produce hydrogen, dilute H2SO4 is poured
from the dropping funnel into the Wolfe's bottle which consists of granulated zinc.
The CuSO4 crystals can be added as a positive catalyst. As H2 gas is lighter than air
it is collected by downward displacement of water.
Precaution
i. The zinc used must not be pure.
ii. Concentrated H2SO4 should not be used instead of dilute H2SO4 because of the
oxidizing nature as conc. H2SO4 reacts with zinc metal and gives SO2 not H2
iii. Nitric acid cannot be used because with zinc it liberates nascent hydrogen and
that reduces the acid into the oxides.

11. Physical Properties
1. It is colorless, orderless and tasteless.
2. It is insoluble in water.
3. It can be liquefied at high pressure and low temperature.
4. It is the lightest gas having very low density.
5. It is neutral to litmus.
Chemical Properties
The bond dissociation energy of hydrogen molecule is 436 KJ mol and atomic size is
very small. Due to these reasons, it is less reactive in nature in nature. However,
it reacts with metals, non-metals and other compounds under suitable conditions.
1. Hydrogen is a stable molecule.
2. Action with metals:
a) With reactive metals like: Na, K, Ca etc. respective hydrides are formed.
2Na +H2→ 2NaH
b) With less reactive metals:Finely divided metals like palladium (Pd), platinum (Pt),
nickel (Ni), cobalt (Co) etc. absorb hydrogen to form interstitial hydrides.

12. 3. Action with non-metals:Hydrogen reacts with the number of non-metals under the
specific condition.
a) With oxygen:When hydrogen is heated with oxygen water is produced.
2H2 + O2 −−−→ 2H2O
b)With halogens:Hydrogen reacts with halogens to produce hydrogen halides.
Reactivity of hydrogen decreases from fluorine to iodine.
dark
H2 + F2 −−→ 2HF
sunlight
H2 + Cl2 −−−−−→2HCl
673K
H2 + Br2 −−−→2HBr
713K/Pt
H2 + I2 −−−−−→2HI

13. c) With nitrogen:
When nitrogen is treated with hydrogen about 773K and in the presence of
catalyst Fe & Mo as a promoter under a pressure of about 200 atmospheric
pressure, ammonia gas is formed. The reaction is reversible and exothermic.
N2 + 3H2 ⇌ 2NH3 + Heat
d) With sulphur:
Sulphur when heated with hydrogen, produces hydrogen sulphide (H2S).
700K
S8 + 8H2 −−−→8 H2S
e) With carbon:
Hydrogen reacts with carbon on heating to produce hydrocarbons.
1373K
C + 2H2 −−−→CH4
1773K
2C + 3H2 −−−→C2H6

14. 4. With other compounds:
a) With metal oxides:
Hydrogen is a reducing agent. So, it reduces metal oxides into pure metals.
Δ
CuO +H2 −→Cu + H2O
Δ
MgO +H2 −→ Mg + H2O
Δ
F e3O4 +4H2−→ 3Fe + 4H2O
b) With carbon monoxide:
Carbon monoxide reacts with hydrogen on heating about 537K and in the
presence of catalyst ZnO and Cr O atmos. pressure to get methyl alcohol
(methanol).
573K ZnO,Cr2O3 (200 atom)
CO + H2 −−−−−−−−−−−−−−−−→CH3OH
c) With unsaturated hydrocarbon:
Unsaturated organic compounds like ethene (CH2 = CH2) reacts with hydrogen to
produce saturated organic compounds like ethane. This reaction takes place in
the presence of Ni, Pb or Pt powder on heating at about 473K.
Ni or Pd or Pt
CH2 = CH2 + H2 −−−−−−−−−→ vegetable ghee (fat)

15. Hydrogen Sulphide (H2S)
Hydrogen Sulphide is prepared by the action of dilute hydrochloric acid on iron(II)
sulphide.
FeS + HCl-----------------> FeCl2 + H2S
The liberated gas is collected above warm water (since it readily dissolves in cold
water) or by downward delivery.

16. H2S cannot be prepared by treating FeS with HNO3 because H2S once formed may
reduce nitric acid to NO2 and H2S is itself oxidized.
2HNO3 + H2S→ 2H2O + 2NO2 + S
And conc. H2SO4 cannot be used for the preparation ofhydrogen sulphide because
conc. H2SO4 behaves as an oxidizing agent and oxidizes hydrogen sulphide to
sulphur. H2S + conc. H2SO4 → 2H2O + 2SO2 + S
Physical Properties
1. Hydrogen sulphide is colourless gas with rotten-gas smell;
2. It turns litmus paper red, because of the acidic nature of the gas
The gas is about 1.25 times denser than air, Purification of gas
H2S gas is purified by passing heat through the suspension of MgO.
MgO + 2H2S⟶Mg(HS)2 + H2O
Mg(HS)2→H2S ↑ +MgS

17. Preparation of H2S by Kipp's Apparatus
Principle
Hydrogen sulphide gas is prepared in Kipp’s Apparatus by action of HCl on FeS.
FeS + HCl-----------------> FeCl2 + H2S
For analytical purpose, H S gas is needed in small quantity in the regular interval in
small quantity. For this purpose, Kipp'sapparatus is used. It contains bulbs 'A',
'B' and'C' in which bulb 'A' has a long stem that connects bulb 'B' and 'C' as
shown in
the figure.

18. Working process
The middle bulbs contain iron sulphide pieces. Dil H2SO4 is poured from the top of
bulb A. When acid just covers the FeS pieces after filling the bulb C reactions starts
to give H2S gas and comes out when the tap is open.
FeS + H2SO4⟶FeSO4 + H2S ↑
When the tap is closed, the gaseous pressure in bulb 'B' increases that pushes H2SO
up, up to the bulb 'A' which breaks thecontact between acid and FeS and hence the
formation of gas is stopped. When the tap is open H2S gas comes out and acids come
in place of H2S and this process repeats.

19. Test of H2S
It has a pungent smell(rotten egg odour) and is tested by passing it through the
filter paper wetted by lead acetate which
turns into black.
Physical Properties
1. It is colourless gas with the pungent smell of rotten egg.
2. It is heavier than air.
3. It is fairly soluble in gas.
4. It is poisonous gas.

20. Laboratory Preparation of SO2 gas
Principle
In the laboratory, SO2 gas is prepared by the action of cupper turnings with
concentrated sulphuric acid.
Cu + 2H2SO4⟶CuSO4 + H2O + SO2
Hence, formed gas is collected in the gas jar by upward displacement of air.

21. Procedure
Cupper turnings pieces are taken in a round bottom flask. Conc. H2SO is poured
through thistel funnel and apparatus is made air tight as shown in figure. After
heating the flask, SO2 gas is formed which can be dried by passing it through
conc. H2SO4 in order to absorb moisture, pure and dry gas is obtained in the gas
jar by upward displacement of air.
Physical Properties
1. It is a colour gas with a pungent suffocating odour.
2. It is 2.2 times heavier than air.
3. It is highly soluble in water and the solution is called sulphurous acid.
4. It can be easily liquefied to a colourless liquid at -10°C and solidified at -26°C.

22. Preparation of Ozone
Ozone is best prepared by silent electric discharges through pure and dry oxygen.
3O2 ⇌ 2O3 − 96 cal
Different types of ozonizers can be used for this purpose. The ozonizer contains an
annular space between two tubes through which oxygen passes. In Siemen's
ozoniser, the inner tube is of iron or glass and it's concentric with outer one of
glass, partly coated with tin foil. Both these are connected to the two secondary
terminals of an induction coil and the ozone produced is continuously swept out
by the fresh current of oxygen.

23. Preparation of ethene
In the laboratory ethene is prepared by dehydration of ethanol. On heating ethyl
alcohol with sulphuric acid at a temperature of 170 °C temperature forms ethene.

24. Physical properties
 Ethene is a colourless gas.
 Ethene posses pleasant odour at STP.
 Ethene is completely soluble in organic solvents and slightly soluble in water.
 It is lighter than air.
 Boiling point of ethene is -102 ° C and melting point is: –169° C.
 It has anaesthetic effect on inhalation.
Chemical properties
1. Reactivity:
Ethene is more reactive than ethane and methane, as it has a double bond. The
double bond is weaker than single bond. Hence, it can be readily attacked any
other reactant. The typical reactions of alkenes involve the breaking of the
double bond to form two single bonds. Such reactions are called addition
reactions.
2. Combustion
Ethene on combustion produce carbon dioxide, water and heat.
C2H4 + 3O2 → 2CO2 + 2H2O + Heat

25. Addition of hydrogen to ethene: Gives ethane after catalytic hydrogenation in
presence of nickel.
Addition of chlorine: When treated with halogens, forms 1, 2, dihalo ethanes.
Polymerisation: Polymerisation is a process in which large number of unsaturated
hydrocarbons join together to form a big molecule. The big molecule formed in
this process is called a polymer.
The polymer polythene is formed by the polymerisation of ethene at high
temperature and pressure.

27. Test of Ethene
Two common qualitative tests for unsaturation are the reaction of the compounds
with bromide in carbon tetrachloride and with potassium permanganate.
1. Bromine in Carbon Tetrachloride
Bromine will add to the carbon-carbon double bond of alkenes to produce
dibromoalkanes, characteristic dark red-brown color disappears at the end of
reaction.Which indicate the presence of unsaturation.

28. Potassium Permanganate (Baeyer Test)
A second qualitative test for unsaturation, the Baeyer test, depends on the ability
of potassium permanganate to oxidize the carbon-carbon double bond to give
alkanediols only ethene gas gives both test and ethane doesn't give such tests.

29. Laboratory Preparation of Ethyne
Ethyne is prepared by the action of water on calcium carbide.
CaC2 + 2H2O → Ca(OH)2 + C2H2
A thin layer of sand is spread atomic the bottom of a conical flask. A few small
pieces of calcium carbide (CaC2) are placed over the sand. The whole apparatus
is set upon. Water is added to the flask drop wise with the help of a thistle funnel.
Ethyne (acetylene) gas so produced is collected in a gas jar by the downward
displacement of water.