Mixtures and Solutions
Objective
The student knows that matter has measurable physical properties and those properties determine how matter is classified, changed, and used. The student is expected to demonstrate that some mixtures maintain physical properties of their ingredients, such as iron filings and sand; and to identify changes that can occur in the physical properties of the ingredients of solutions, such as dissolving salt in water or adding lemon juice to water.
Foundation
A mixture is a combination of two or more different substances. The primary characteristic of a simple mixture is that the substances mixed together do not react chemically and can be separated by various processes. There is no new substance formed. Mixtures can have substances that are evenly distributed or not evenly distributed. Homogenized milk is a mixture of cream and butterfat particles in skim milk. The cream, butterfat, and skim milk are all evenly distributed in the liquid. A mixture of stones in soil is an example of an uneven distribution.
Mixtures can be combinations of solids, liquids, or gases. Sand and gravel is an example of a mixture of solids. Muddy water is an example of a solid and liquid mixture. An example of a solid and gas mixture would be smoke, which is a mixture of solid and liquid particulates and gases based on what is burning. Wood smoke is mainly warm air, dust, tiny particles of wood, and ash. Water and oil is an example of a two-liquid mixture. Fog is an example a liquid and gas mixture consisting of small water particles and air. A carbonated drink like Coca Cola is a mixture of gas and liquid. Left open, the gas will escape leaving a drink that tastes flat with no “fizz.” In each case, there are two or more substances that have been mixed together.
Mixtures can be separated back to their individual substances through a variety of procedures. Sometimes, the properties of the substances mixed together can be used to separate them. In an oil and water mixture, the oil will eventually separate and rise to the top because oil is lighter and less dense than water. In a sugar/water mixture, however, since the sugar dissolves in the water, it is not going to ‘settle’ out or be strained out. By heating a sugar/water mixture, evaporation of the water will leave the sugar back in its crystalline state. Some mixtures, such as sand and gravel, can be separated by sifting through a strainer. Some mixtures can be separated by using magnets if one of the substances is a form of iron.
Mixtures of certain substances such as sugar in water form solutions. Solutions are formed when one substance mixes homogeneously into another substance such as sugar dissolving in water. Solutions can be solid, liquid, or gas. Examples of solutions include brass (solid), soda (liquid), and air (gas).
Mixtures are combinations of materials which do not undergo a chemical reaction or change when mixed and can be separated back to their original state through various mechanical processes. Solutions are formed when the substances mix homogeneously, and often require different methods to separate the substances.