Essay Molecules: Colloids

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C13 Colloids
This topic focuses on a variety of colloidal systems and stresses their importance in everyday life. Hand cream, salad cream and milk are all emulsions. For example, milk is an emulsion of fat droplets in water. Jelly baby sweets are a gel and muddy river water is a sol. Fog or mist is an example of a colloid called an aerosol.

|Syllabus Core |Page |Notes |
|Know that a colloid consists of one substance finely dispersed in another|p1 & 2 |of this booklet and |
|and know the meaning of the words sol, gel and emulsion |p4 |of the “Unit 11 Colloids Information” document |
|Know that colloidal systems are not | | |
|transparent; | | |
|Appreciate the purpose of emulsifiers | | |
|Supplement | | |
|Understand that colloidal systems are not transparent because they | | |
|scatter light rays | | |
|Understand, in simple terms, the action of emulsifiers | | |

Know what colloids are

Look at the photos on p164-168 of Nuffield Co-ordinated Sciences Chemistry (p 1 – 3 Word doc) and write down some examples of colloids below.
Some examples of colloids:
1. Emulsion paint

2. Cosmetic emulsions

3. Butter

A continuous phase and a disperse phase

Colloids are everywhere and all the different types of colloids have something in common; they consist of a mixture of two substances which cannot mix.

“Every colloid has at least two parts. One part is the continuous phase like the water in milk or the air in mist. The other part is split up into minute particles like the fat in milk or the water droplets in mist. These scattered particles make up the disperse phase.”
Read p164 −168 of Nuffield Co-ordinated Sciences Chemistry and then fill in the gaps in the passage that follows from p165. (page 1 of “Unit 11 Colloids Information”)

“One way or another, many of the things we take for granted involve colloids. Colloids muddle up the simple idea that everything is either a solid, a liquid or a gas . A colloid is made by mixing two things which cannot mix!. This sounds stupid until you look at some examples and think about the meaning of the word “mix“. Thus, the trick to understanding the topic of colloids is to stop and think about how different mixtures are described. It also helps to understand the technical meanings of some of the words used to describe colloids.
“There are eight different types of colloid made by ....................... ......... .............. ..... ......... ....................... ..... ................... .” p168 Nuffield (p 4 of “Unit 11 Colloids Information” – WORD doc).

Fortunately, the syllabus only requires us to memorize only three types:

Know the meaning of the words SOL, GEL and EMULSION.

A sol is a solid dispersed in a liquid. e.g. paint
A gel is a liquid dispersed in a solid. e.g. jelly or butter
An emulsion is one liquid dispersed in another liquid. e.g. salad cream, milk or hand cream
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