The document discusses the chemical alkynes, specifically ethyne (C2H2). It describes the laboratory preparation of ethyne from calcium dicarbide and water, which produces ethyne gas. Ethyne is colorless, insoluble in water but soluble in nonpolar solvents, and burns with a very hot, smoky flame when combusted. It can be used to cut and weld steel in oxy-acetylene torches. The document also discusses the manufacture and uses of hydrogen, including from natural gas reforming and electrolysis of water, and its use in the Haber process and as a fuel. Fuel cells that use hydrogen are also mentioned.
4. Laboratory Preparation of ethyne
Calcium dicarbide [CaC2] is a grey lumpy solid.
Reacts very exothermically with water
[Fizzing and steam produced as it reacts]
Calcium hydroxide is a white powder with a
greater volume
Acidified Copper Sulphate solution removes
impurities such as phosphine gas - produced
when calcium phosphide impurity reacts with
water.
5. Physical Properties
Ethyne
is a colourless gas with a sickly sweet
smell.
It is insoluble in water but soluble in non
polar solvents like cyclohexane.
6. Combustion
Ethyne
burns in oxygen with a very smoky
yellow flame
In excess pure oxygen it burns with a very hot
flame [3150oC] 1299 kJ mol-1
This is used to cut and weld steel.
Old name for ethyne is acetylene hence oxyacetylene torch or burner
8. Uses of Ethyne
Ethyne
is used in the oxy-acetylene torch to
cut and weld steel
9. Manufacture of Hydrogen
Steam
Reforming of Natural Gas
CH4 + H2O = 3 H2 + CO
In
presence of a suitable catalyst
10. Manufacture of Hydrogen
Electrolysis
of Water
using dilute H2SO4
forms
at cathode [negative electrode]
Overall
Too
H2O = H2 + 1/2 O2
expensive in most parts of world
11. Uses of Hydrogen
Haber
Process for producing ammonia
N2 + 3 H2 = 2 NH3
Hydrogenating
vegetable oils
12. Uses of Hydrogen
Fuel
- about 10% of worlds production of
hydrogen is used as fuel
Environmentally friendly
Water is the only product of combustion
H2 + 1/2 O2 = H2O
It is explosive with air
Difficulties with storage and transport