Kitchen Chemistry

Cooking with a hydrophobic (water hating) liquid .
We call it oil.

Cooking with oil has some great advantages.
Firstly it can heat up to temperatures well above 100 ^oC, water can only be heated to 100^oC. This makes food cook faster at higher temperatures.

Secondly oil is hydrophobic. As the name implies it is water fearing. Oil and water repel each other and do not mix. These two characteristics also make oil very dangerous in the kitchen.

When you put dough into the deep fryer the temperature of the oil causes the surface of the dough to quickly cook and become crispy while the inside remains soft. Since oil and water do not mix the dough will not become wet and soggy.

Another characteristic of oil is that it is less dense than water so it floats on the surface of water. Using two of these properties of water, namely that it is hydrophobic and less dense than water we can make some cool demonstrations.

Let's start. You will need some food dye, some oil of course, a glass cup, a very small bowl and some water. See the image on the right.

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Place about 4 tablespoons of oil into a small bowl and drop 4 drops of each colour into the oil, making sure each drop is well separated from another drop of food dye.
Does the food dye and oil mix?

Now pour the oil and food dye mixture on the surface of a glass of water, as shown on the right.

Observe the display of colours as they fall and swirl in the water.

Do you think the food dye is hydrophobic like the oil or does it dissolve in water?

Explain how this comes about using the properties of oil.