1. Other Chemical
Fuels

2. Alkynes

General formula
CnH2n-2

First member
ethyne

Functional group
-C≡C-
C2H2

3. Laboratory Preparation of ethyne
CaC2(s) + 2 H2O(l) = Ca(OH)2(s) + C2H2(g)

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

7. Tests for Unsaturation
 Ethyne
 Ethyne
decolourises bromine water.
decolourises acidified potassium
manganate(VII) (potassium permanganate.

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

13. Fuel Cell