Re: What melts faster butter or margarine? Why?

You have a very good question. The answer is that the margarine you used has 
more unsaturation than butter so melts at a lower temperature. These fatty 
acids are made up of carbon, hydrogen, and oxygen atoms. They can have any 
number of carbons. Usually the number of carbons is even. So, we have fatty 
acids with 2, 4, 6, 8, and so on, carbons.  As we add carbons we increase 
the melting point. So a fatty acid with 2 or 4 carbons is likely a gas at 
room temperature while one with 10 will be a liquid and one with 16 or more 
will be solid. 
There is another difference in fatty acids that can change the melting 
point. That is something called the degree of unsaturation or the number of 
double bonds. What is a double bond? Well, most of the carbons except the 
ones at the end of the carbon chain have two hydrogens and are saturated. 
Sometimes two carbons that are side by side only have one hydrogen each. We 
say those carbons are unsaturated. (They are double bonded.)  If only two 
carbons in a fatty acid are unsaturated we say the fatty acid is 
monounsaturated.  Mono means one. So, monounsaturated means only one pair of 
unsaturated carbons 
If we have several pairs of carbons with only one hydrogen per carbon, we 
say the fatty acid is polyunsaturated. Poly means many. So, a 
polyunsaturated fatty acid has many pairs of unsaturated carbons.
As the numbers of pairs of unsaturated carbons increases in a fatty acid, 
the melting point decreases. See Table 1 below.

Table 1. Fatty acid melting point and number of carbons
Fatty Acid		Pairs of unsaturated carbons	Melting point in oC
Stearic		0						69.7
Oleic			1						10.5
Linoleic		2						-5
Linolenic		3						-11
		
Note that Stearic acid is a solid at room temperature. Oleic acid is a 
liquid a room temperature but if you put it in a refrigerator it will go 
solid. The other two fatty acids are liquid at room temperature and in the 
refrigerator.
Before going on, there is one more piece of information you need. We do not 
find fatty acids free in nature. They are always part of something we call a 
triglyceride. We use the short form TG to stand for a triglyceride.

When you put butter in the refrigerator it goes very hard and if you take it 
out of the refrigerator and try to spread it, it tears your bread. Most 
people do not like this. So several years ago, the food scientists decided 
to do something about that. They knew all the information we have talked 
about so far. A liquid TG like say sunflower or corn oil, has unsaturated 
fatty acids. Food scientists thought that if they could remove some of the 
unsaturation by making the unsaturated carbons saturated, they should be 
able to make the oil a solid both at room temperature and at the temperature 
of the refrigerator. They wanted to find the amount of unsaturation they 
needed so even if the product was put in the refrigerator, you could take it 
out and spread it on your bread without tearing the bread. 
They have succeeded in getting margarine that is easy to spread even when 
you take it right out of the refrigerator. They do this by a process called 
hydrogenation. In this process, some unsaturated carbons become saturated. 
Something else happens during hydrogenation too. In nature, all the 
unsaturated carbons are cis. During hydrogenation some of them become trans. 
Don’t worry what cis and trans mean.  There is one thing that trans 
unsaturation does. It makes fatty acids have a higher melting point. For 
example the 18 carbon fatty acid with two pairs of unsaturated carbons has a 
melting point of –11oC if it is cis and +15oC if it is trans. 

So the most likely reasons your margarine melted at a lower temperature than 
butter is because the margarine had more unsaturation than the butter. It 
started out as an oil and only some of the unsaturation was removed. 

I hope this makes sense. 
Good luck with your science and keep up the good work.