Understanding Mixtures and Solutions in Chemistry

Unit 3: Mixtures & Solutions

Mixtures

1. Mixtures

A mixture is a sample of matter which is formed by two or more different components that are not bound and without any fixed proportions to each other. For instance, if you look at a granite rock, you can easily distinguish between a gray portion, some black dots, and some crystals which reflect the light. Granite is a mixture composed of quartz, feldspar, and mica.

Almost everything you can find is a mixture because even a pure substance, such as distilled water, has a few impurities, such as salt.

2. Homogeneous Matter

A phase is a portion of homogeneous matter which is uniform throughout. In other words, it has the same appearance and physical properties everywhere.

3. Heterogeneous Mixtures

On a general basis, we can classify mixtures into two different types: heterogeneous and homogeneous mixtures. A heterogeneous mixture is one which visibly has several portions of matter or phases of different appearances. In other words, in a heterogeneous mixture, we can see a boundary or a surface which separates at least two different portions.

For instance, a vinegar and oil salad dressing is a heterogeneous mixture because we can see a layer of oil at the top of the mixture and a vinegar layer at the bottom, which lets us distinguish them easily.

Other examples of heterogeneous mixtures are the beach sand, which has particles of different colors, cereals in milk, or water and steam inside a pressure cooker. Remember that the prefix “hetero” means difference.

Activity 1

Classify some of these mixtures into homogeneous and heterogeneous: granite, wine, coke, a sample of soil, air with dust, sea water, apple juice.

Activity 2

Try to explain why the oil splashes when some drops of water fall into the pan. Furthermore, these portions have different physical properties (e.g., boiling point, color, etc.) and consequently, they can be easily isolated using separating methods which don't change the state of the sample. These methods are called physical separation methods because no chemical processes are involved.

Most Important Physical Separation Methods

1. Magnet Separation: If one of the components of the mixture has magnetic properties (e.g., iron, nickel, etc.) and the other does not, we can use magnet separation. A magnet attracts the portions of iron and the rest can be discarded.
2. Filtration: We use filtration to separate an insoluble solid from a liquid. For instance, a mixture which consists of sand and water can be separated by pouring the mixture through a filter paper placed in a funnel.