PROPERTIES OF ALKANES
Properties of alkanes
Alkanes are colourless gases, solids and liquids that are not poisonous.
They are slightly soluble in water.
The solubility decrease as the carbon chain increase.
The melting and boiling point increase as the carbon chain increase.
This is because of the increase in van-der-waals / intermolecular forces as the carbon chain increase.
The 1st four straight chain alkanes (methane, ethane, propane and butane) are therefore gases
The next six (pentane ,hexane, heptane,octane,nonane, decane) are liquids.
From unidecane ,alkane with 11 carbon atoms are solids .
The density of straight chain alkanes increase with increasing carbon chain as the intermolecular forces increases.
This reduces the volume occupied by a given mass of the compound.
Summary of physical properties of alkanes
|
Alkane |
General formula |
Melting point(K) |
Boiling point(K) |
Density gcm-3 |
State at room(298K) temperature and pressure atmosphere (101300Pa) |
|
Methane |
CH4 |
90 |
112 |
0.424 |
gas |
|
Ethane |
CH3CH3 |
91 |
184 |
0.546 |
Gas |
|
Propane |
CH3CH2CH3 |
105 |
231 |
0.501 |
gas |
|
Butane |
CH3(CH2)2CH3 |
138 |
275 |
0.579 |
gas |
|
Pentane |
CH3(CH2)3CH3 |
143 |
309 |
0.626 |
liquid |
|
Hexane |
CH3(CH2)4CH3 |
178 |
342 |
0.657 |
liquid |
|
Heptane |
CH3(CH2)5CH3 |
182 |
372 |
0.684 |
liquid |
|
Octane |
CH3(CH2)6CH3 |
216 |
399 |
0.703 |
liquid |
|
Nonane |
CH3(CH2)7CH3 |
219 |
424 |
0.708 |
liquid |
|
Octane |
CH3(CH2)8CH3 |
243 |
447 |
0.730 |
liquid |
state the general properties of alkanes