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  1. Olive oil consists of almost 100% of fat. As you can see in the table of contents below, it includes both unsaturated, monounsaturated and polyunsaturated fats in the oil.

Nutrition declaration per 100 ml (= 92 g) Energy 3390kJ / 823 Kcal Fat 92 g Carbohydrate 0 g Of which saturated fat is 13 g Of which sugars are 0 g Monounsaturated fat 68 g Protein 0 g Polyunsaturated fat 7.2 g Salt 0 g

If you add bromine water, Br2 (aq), to the olive oil, its consistency changes significantly and it becomes more viscous. What is it that happens chemically with the olive oil when adding bromine water and why does it become more viscous?


marked as duplicate by Karsten Theis, Ivan Neretin, Mithoron, Todd Minehardt, Mathew Mahindaratne May 1 at 1:13

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It is a similar process to hydrogenation of plant oil on Raney nickel, producing margarines.

The saturated fats have zig-zag structure of $\ce{C-C}$ chain, what makes them good in "molecule spooning", leading to high melting point.

The addition of bromine had a similar effect.

OTOH the cus double bonds of oils are obstacles for "spooning" and the menting point is low.

The bromine is, AFAIK, used to determine the amount of unsaturated bonds in edible oils.

$$\begin{align} \small \ce{ \\ \small -CH2-CH=CH-CH_2 - + H2 &->[Ni] \small -CH2-CH2-CH2-CH_2 -\\ \small -CH2-CH=CH-CH_2 - + Br2 &-> \small -CH2-CHBr-CHBr-CH_2 -\\ }\end{align}$$


Fatty acids are components of many types of lipids. Fatty acids are carboxylic acids with very long hydrocarbon chains, usually consists of 12-18 carbon atoms long hydrophobic chain. Olive oil is a liquid obtained from olives, which contains mixture of fatty acids. According to Wikipedia:

The composition of olive oil varies with the cultivar, altitude, time of harvest and extraction process. It consists mainly of oleic acid (up to 83%), with smaller amounts of other fatty acids including linoleic acid (up to 21%) and palmitic acid (up to 20%).

The main component of olive oil, oleic acid, is a monounsaturated fatty acid (FA; See Table) and generally average about 70% in olive oil. Another monounsaturated FA, palmitoleic acid averages in the range of 0.3-3.5%. Olive oil also contains polyunsaturated FAs such as linoleic acid (~15%) and $\alpha$-linolenic acid (~0.5%). Only about 20% saturated FAs (see Table)) are present in olive oil and most of them are palmitic acid (~13.0%) and stearic acid (~1.5%).

Structures of Common Fatty Acids (saturated), of which, palmitic (~13.0%) and stearic acid (~1.5%) are present in olive oil: $$ \begin{array}{ccc} \text{Name of FA} & \text{# of carbons} & \text{Structure} & \text{Melting Point} \\ \hline \text{Lauric acid} & 12 & \ce{CH3(CH2)10CO2H} & \pu{44 ^{\circ}C} \\ \text{Myristic acid} & 14 & \ce{CH3(CH2)12CO2H} & \pu{58 ^{\circ}C} \\ \text{Palmitic acid } & 16 & \ce{CH3(CH2)14CO2H} & \pu{63 ^{\circ}C} \\ \text{Stearic acid} & 18 & \ce{CH3(CH2)16CO2H} & \pu{70 ^{\circ}C} \\ \hline \end{array} $$

Structures of Common Fatty Acids (unsaturated), three of which, oleic acid (~70%, linoleic acid (~15%), and $\alpha$-linolenic acid (~0.5%) are present in olive oil:

$$ \begin{array}{ccc} \text{Name of FA} & \text{# of carbons} & \text{Structure} & \text{Melting Point} \\ \hline \text{ Palmitoleic acid} & 16 & \ce{CH3(CH2)5CH=CH(CH2)7CO2H} & \pu{-1 ^{\circ}C} \\ \text{Oleic acid} & 18 & \ce{CH3(CH2)7CH=CH(CH2)7CO2H} & \pu{4 ^{\circ}C} \\ \text{Linoleic acid} & 18 & \ce{CH3(CH2)4CH=CHCH2CH=CH(CH2)7CO2H} & \pu{-5 ^{\circ}C} \\ \text{ Linolenic acid} & 18 & \ce{CH3CH2(CH=CHCH2)2CH=CH(CH2)7CO2H} & \pu{-11 ^{\circ}C} \\ \hline \end{array} $$

According to the melting points of FAs in olive oil, one can conclude that it contains a lot of double bonds (mostly mono-unsaturated). These unsaturated fatty acids contain only cis-double bonds (e.g., oleic and linoleic acid). The presence of cis-double bonds has an important lowering effect on the melting point of the fatty acid (see Table), because cis-double bonds form rigid kinks in the fatty acid chains (see the picture of oleic acid):

Oleic acid

Keep in mind that there is no rotation around a double bond, and as a result, the unsaturated fatty acids cannot line up very well to give a regularly arranged crystal structure. On the other hand, saturated fatty acids would line up in a very regular manner, better than that of unsaturated, leading to better van der Waals-forces, thus get closer together (thicker). This is one of the reasons why they are solids in ambient conditions with high melting points (see Table).

Now, what happens when you add bromine water to olive oil? Bromine added to double bond (same reaction as clarification test for unsaturation), making the fatty acid saturated. For example, when $\ce{Br2}$ added to $\ce{C18}$ oleic acid (m.p.: $\pu{4 ^{\circ}C}$), it'd become a resemblance of $\ce{C18}$ stearic acid (m.p.: $\pu{70 ^{\circ}C}$) with two extra $\ce{Br}$ atoms replacing 2 $\ce{H}$ atoms. Now you see why olive oil getting thicker!


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