This GCSE Chemistry quiz is all about emulsions. Emulsions are mixtures of two or more liquids that are non-soluble with one another. They are immiscible. A good example is water and vegetable oil. These are non-soluble with each other so when you mix a vegetable oil with water, you will see two distinct layers. This is because many oils are less dense than water and therefore float on top. You make the oil and water mixtures into emulsions simply by shaking the two liquids together. The oil breaks up into droplets and becomes dispersed (scattered) through the water. We call this an 'oil in water' emulsion. If it is the water that disperses through the oil then you have a 'water in oil' emulsion. Whichever type of emulsion you make, leave it to stand and you will notice that it soon separates. We say that the emulsion 'breaks'.
It is possible to make a much more stable emulsion by using an emulsifier. This keeps the droplets dispersed for a much longer time. Emulsifiers are added to many foods in order to make sure that they are more appealing. Egg yolk contains a natural emulsifier which is what holds the vinegar and vegetable oil together in mayonnaise. Another common food additive is the emulsifier lecithin which is a totally natural emulsifier that is extracted from seeds. It isn't a single substance, it's a mixture.
For higher tier candidates, you need to know that an emulsifier is a molecule that has at least one part, the head, that likes to dissolve in water (hydrophilic or water loving) and at least one other part, the tail, that likes to dissolve in oil (hydrophobic or water hating). The hydrophilic end remains in the water and the hydrophobic end dissolves in the oil droplets, surrounding them and keeping them apart.
For the GCSE, you need to know some examples of where emulsions are used, but that's not too difficult as they are things you meet in your daily life - milk, salad dressings, paint, cosmetics ... the list is long. What is a little harder is to remember whether they are oil in water (milk, ice cream, salad cream, mayonnaise) or water in oil (margarine, butter, skin moisturising cream).
Try this quiz and see if you understand emulsions and how we can make mixtures of non-soluble liquids.
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