why does methanol have a low boiling point
Alcohols all contain the вOH group and this is generally responsible for their chemical properties and reactions. They are named after their вparentв alkane Hydrocarbon in which all the carbon-carbon bonds are single covalent bonds. , for example: methanol (alcohol) and methane (вparentв alkane); ethanol (alcohol) and ethane (вparentв alkane). Methanol can be used as a chemical вfeedstockв (starting material for other chemical reactions), in anti-freeze and in the production of
biodiesel A fuel that consists of long organic molecules (specifically, esters) which are obtained by processing crops. Ethanol can be used as a solvent A solvent is the liquid in which the solute dissolves to form a solution. and as a fuel. Short-chain alcohols like methanol and ethanol have a low boiling point (ie lower than water) because they have weak intermolecular force Attractive forces between molecules. which are easily overcome.
Longer chain alcohols have higher boiling points. Alcohols have higher boiling points than their corresponding alkane (eg ethanol has a higher boiling point than ethane) because the вOH group has the effect of strengthening the intermolecular forces. Short chain alcohols are very soluble Able to dissolve (usually in water). in water because of the effect of the вOH group that is strongly attracted to water molecules. Longer chain alcohols are less soluble because they behave more like an alkane and tend to float on top of the water. Alcohols are good fuels because of the presence of the hydrocarbons A group of organic compounds made up entirely of hydrogen and carbon. chain.
They burn in a good air supply to produce carbon dioxide and water. For example: Methanol is polar and with its -OH can form hydrogen bonds. Therefore its intermolecular forces are much stronger than the similarly sized oxygen. Intermo lecular forces must be overcome in order to boil something, so methanol will have a higher boiling point. A quick note on the "similarly sized" comment I made. Whoever it was who assigned you this question wisely made it an easy comparison by chosing two compounds with the same number of electrons (16). There is a huge misconception that exists surrounding intermolecular forces----that molecules with hydrogen bonding or are polar always have stronger intermolecular forces than non-polar molecules. This simply isn't true. Non-polar molecules are held together by dispersion forces, temporary dipoles caused by shifting electron clouds, and unlike hydrogen bonding and polarity, dispersion forces scale with size.
More electrons means more frequent and bigger fluctuations in the electron cloud and leads to stronger and stronger dispersion forces. This is why non-polar I2 with all its electrons is a solid, while methanol with its dispersion, dipole-dipole, and h-bonding forces is a liquid. By giving you two compounds with the same number of electrons, your teacher was basically requiring that the dispersion forces be comparable to each other, thus eliminating that as a variable. If you are using this to answer a homework question, you might want to talk about dispersion forces and how they are similar for these two compounds with the same number of electrons.
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