Why butter solidify at room temperature but not mustard oil?

Question

Why butter solidify at room temperature but not mustard oil?

Answer 1

This is because butter primarily contains saturated fats, whereas oils primarily contain unsaturated fats.

The fatty acid chains of saturated fats are straight, enabling them to lie together in a compact configuration.  This compact structure raises the melting point, and this is what allows butter to remain solid at room temperature.

In unsaturated fats, the fatty acid chains contain kinks and bends where carbons are double-bonded.  Because they aren't straight, they can't lie next to each other as tightly and rigidly as with saturated fats.  Because they're not as compact, this lowers the melting point, and this is why oils are liquid at room temperature.

Answer 2

why plastic, steel, and glass.... but not water?

i know that that may not make sense, but everything has a melting point... some things are higher (or lower) than others.

Answer 3

This has to do with Animal fat having more saturated trigylcerides than vegetable fats, which have unsaturated triglycerides.

Fats and oils are made of triglycerides. Triglycerides have three fatty acid tails (long chain of carbon atoms,like 22 or more). These tails are pack together when they are cold.

Now these tails can be saturated or unsaturated.

Saturated means that the bonds of long carbon chains are all filled with hydrogen, i,e, (-CH2-CH2-CH2-....CH2-CH2-CH3) This has the effect of keeping the fatty acid tails in a straight line. This means when that when it's cold these fatty acid tails can pack very close to each other and become a solid. Thus it takes more heat (higher temperature) for them to melt.

Unsaturated means that some of the carbons aren't completely filled with hydrogen and instead form double bonds with adjacent carbons.

Fatty acids:

...-CH2-CH2-CH2-CH=CH-CH2-CH2-CH=CH-CH...

Notice that the fourth and fifth carbon (from the left) formed a double bond, and eight and ninth carbon is also double-bonded.

Double bonds in fatty acids changed the bond angle from 180deg (straight line) to 120 degrees (a bend in the tail). This has the affect of keeping molecules apart and preventing the tight packing that is possible with saturated fatty acid tails. (look up diagram picture of saturated and unsaturated fatty acids to see what I'm talking about)

Thus at room temp, it is hard for vegetable fats to pack closely enough to form a solid like animal fat like butter.

But of course you know that if you add enough heat, butter melts. The molecules vibrate and move apart - eventually liquefying. It no longer can maintain solid form like the oil.

If you cool the mustard oil enough it will solidify, but since it cannot pack its molecules as closely together, it will melt before butter and other saturated fats when brought to room temperature.

Hope that helps

Answer 4

Indog nailed it