As a class, alcohols have a functional group called a hydroxyl group. How does this property explain the face that ethanol, dissolves in water but ethane does not???
2007-03-04 10:12:28 · 5 answers · asked by Mani & Nima A 1 in Science & Mathematics ➔ Chemistry
The first few answers do not do an adequate job of explaining what is observed.
Alcohols do have a functional group called the hydroxyl group (-OH). Water, if you think about it, also has the same functional group (-OH), except unlike the alcohols, it has a simple hydrogen atom attached to the OH.
All molecules that have the functional group OH can undergo a special type of bonding, Hydrogen bonding. The bonds in molecules that contain the OH group are polarized, with more electron density around (or being pulled towards ) the oxygen atom from whatever the oxygen happens to be bonded to (oxygen is more electronegative than Hydrogen, so it always pulls the electron density in the O-H bond away from the hydrogen, towards itself - this is also true of a carbon-oxygen bond [C-O]). Basically hydrogen bonding takes place when the Oxygen atom in one hydroxyl group attracts the hydrogen atom in a second separate hydroxyl group on another molecule (basically drawn like this:
H-O --- H-O-H
because of the limitations of drawing with text, i've had to leave out the carbon-oxygen bond on the first hydroxyl group...but you can imagine the rest of the molecule attached to the OH group in the alcohol.)
This is basic hydrogen bonding. Ethane does not dissolve in water (or alcohol for that matter) because it is LACKING any hydroxyl groups which could hydrogen bond to other hydroxyl groups (in water or alcohol). Ethane is composed of only carbons and hydrogens. At least one oxygen in a hydroxyl group is needed for hydrogen bonding to occur.
2007-03-04 10:28:55 · answer #1 · answered by Cian 5 · 0⤊ 0⤋
Oxygen requires two electrons to fill it's shell. One Hydrogen donates it's only electron, becoming slightly positve with the oxygen becoming slightly negative. The carbon atom to which the oxygen attatches has allready accepted two electrons from the hydrogens and is carring a negative polar shift. The two negative charges repell and dissociate. Same principle for the water molecules, polarisation of the water molecule brings together the hydroxyl ion and the hydrogen ligands. The positive carbon attacts the slightly negative oxygen in the water molecules. This is Hydrophillic behaviour.
With Ethane there is no polar shift and no disociation. water isn't attracted to is and is called hydrophobic
2007-03-04 18:18:50 · answer #2 · answered by bubbyroller2000 2 · 0⤊ 1⤋
Alcohols are "polar" molecules, which means that the electric charge is not evenly distributed in the molecule. The same happens with water. Polar solvents dissolve polar compounds and non-polar solvents dissolve non-polar compounds.
Ethane is "non-polar" (which means that electric charge is evenly distributed in the molecule) and being the solvent polar, (water) it won't dissolve it.
2007-03-04 18:22:12 · answer #3 · answered by the penguin 2 · 0⤊ 0⤋
Ethanol can hydrogen bond with water, due to its -OH group, but ethane can't.
2007-03-04 18:21:57 · answer #4 · answered by Gervald F 7 · 0⤊ 0⤋
Like dissolves like
ethanol is polar, dissolves in water because water is polar
ethane is covalent and not like water
2007-03-04 18:16:32 · answer #5 · answered by science teacher 7 · 0⤊ 1⤋