# Science: A Field Of Wonder/Homogeneous and Heterogeneous Mixtures

   When you slice apples, strawberries, kiwis, pineapples, and grapes, and you mix them all together in a bowl, you have just made a salad that tastes good and healthy. Like salad, many useful things are made by mixing two or more kinds of matter. These are called mixtures.

## Pure Substances and Mixtures

You have learned that a fruit, cheese, spoon, plate, and bowl are matter. Some things are made of only one kind of matter. Sugar is one example. Sugar is made only of sugar. It does not contain any other kind of matter. Sugar is a pure substance. A pure substance is made of a single kind of matter with certain properties. Every part of a substance is the same throughout.
Most of the things around us are mixtures, such as the air, the ocean, the soil, and even food! A box of mixed nuts and assorted marshmallows, pile of leaves and twigs under a tress, and a gallon of ice cream are all mixtures.
A mixture is a physical combination of two or more substances. The substances in a mixture are not chemically combined as they are in a compound. Hence, a mixture is not a pure substance. One important property of mixtures is that proportions of its parts can change. Mixtures have two kinds: homogeneous mixtures and heterogeneous mixtures.
Making a mixtures is a physical change. Mixing together two or more substances often changes the form, color, size, or texture of those substances, but the properties of each substance in the mixture do not change. When you look at the salad, how do you know it is made with different kinds of vegetables? You can pick the onions out of the vegetable salad, and they are still onions.

### Homogeneous Mixture
#### Solution

You have read that when you mix sugar in water, the sugar particles dissolves and thus, you do not see them in water. Sugar-water mixture is a solution. A solution is a homogeneous mixture in which two or more substances are so evenly mixed that the separate parts cannot be seen. The properties of the substances that make up the mixture are the same as they were before they mixed together. That is why you can taste the sugar in the water.
In a sugar-water solution, the sugar has dissolved in water. To dissolve means to mix completely with another substance to form a solution. In a solution of water and sugar, water is the solvent and sugar is the solute.
Water is called as the "universal solvent" because it is capable of dissolving more substances than any other liquid.
Particles in a solution spread evenly throughout the solution. There are solutions, such as lemonade and saltwater, that have a liquid solvent and a solid solute. However, solutions can have other combinations . Soda water is a solution made of carbon dioxide dissolve in water. Air is a solution of several different gases.
Since not all solutions are made by mixing a solid substance with water, many solutions are mixtures of matter in other states.
Some Types of Solutions :
| Types | Examples | Parts |
| gas dissolved in gas | air | oxygen, nitrogen, other gases |
| solid dissolved in solid | steel | iron, nickel, chromium |
| solid dissolved in liquid | ocean water | salt, minerals, water |
| gas dissolved in liquid | soda water | carbon dioxide, water |
Recall that the substances in a solution are evenly mixed that the specific parts cannot be seen. This means that the molecules of the two substances become evenly mixed.

### Heterogeneous Mixture

Another type of mixture is the heterogeneous mixture. Mixing salt in water forms a solution, but mixing soul with water forms another kind of mixture called suspension.
A suspension is a heterogeneous mixture that contains particles huge enough to be seen by your naked eye. These are mixtures from which some of the particles settle slowly when set aside. Examine some liquid food and medicines, if you see Shake before using on the label, it means it is a suspension. Another example of this is soil shaken with water. The soil particles start to settle when the shaking tops.
Take a glass of water and place a handful of sand or dirt. Stir it well. Have you made a solution? Sand and dirt do not dissolve in water. Although it may look homogeneous for a few moments, the sand or dirt gradually sinks to the bottom of the glass. Therefore, it is an example of a suspension.

#### Colloid

Another type of heterogeneous mixture is colloid. A colloid is a mixture that contains particles that are too small to be seen. its particles are intermediate in size between those found in solutions and suspensions and can be mixed such that they remain evenly distributed without settling out.
A colloid is exactly like a suspension, but because the particles are so small, they never settle to the bottom. Milk is a colloid because it scatters a beam of light passing through it; therefore, it shows the Tyndall effect.
Emulsion is a kind of colloid. An emulsion is a mixture of two liquids that do not dissolve. For example, mayonnaise is an emulsion of vegetable oil, egg yolks, and vinegar or lemon juice.
What you see in the picture below is a colloid of water droplets suspended in air. Fog is a mixture of water droplets and air. Even though fog appears to be gas, it is still a heterogeneous mixture because it contains water droplets.
Have you see smoke rising from a barbeque grill? Is smoke a mixture? Smoke is a mixture made up of air, other gases, and tiny solid particles of ash. Dust is another solid that mixes with air.