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Some lemonade is a mixture of lemon juice, water, and sugar.
You know there’s sugar in lemonade, because the drink tastes sweet. But you can’t see the sugar. Why? Because the sugar is completely dissolved in the liquid.
Mixed together, lemon juice, water, and sugar form a solution. A solution is a mixture in which the different kinds of matter are spread out evenly. In lemonade, water is called the solvent. Sugar and lemon juice are solutes. A solute is matter that dissolves in a solvent. The solvent is often a liquid, such as water. If a solution consists of different amounts of two liquids, the solvent is the liquid that there’s more of.
▲ You can make lemonade by mixing water, lemon juice, and sugar.
The Lemony Ticket
Lemonade has properties similar to other solutions.
Once it is completely mixed, a solution is the same throughout. In the example of lemonade, the ratio of sugar to water to lemon juice is the same everywhere in the glass or pitcher.
◀ Ocean water is a solution of salt and water. There are about 2.2 pounds of salt in every cubic foot of ocean water. How much water is in a cubic foot? It’s all the water that would fit in a box one foot high, one foot wide, and one foot deep. If all the salt in the ocean were spread over the land, it would form a layer about as tall as a 40-story building.
Desalination Plant
▲ Scientists have found ways to use evaporation and other methods to create freshwater from ocean water. The process is called desalination. Desalination is important in areas of the world where freshwater is scarce.
Oil
Sand
Pepper
Wood
▲ Sugar and salt form solutions with water easily, but oil, pepper, sand, and wood do not. That’s because of molecules, and the forces that hold them together. A molecule is the very smallest amount of something. For a solution to form, there must be an attraction between the molecules of the solute and the solvent. Here, we’re talking about the molecules of water and oil—or sand or pepper or wood. If that attraction is not strong enough, the solvent does not spread out into the water. That’s why no solution forms.
◀ Water can form a solution with air, and that produces humidity. Like other solutions, air can become saturated with water. When that happens, we say that the relative humidity is 100 percent. As the temperature cools down, the air can hold less water, and that leads to rain.
Fog
Mud
▲ Mud puddles and fog are mixtures, but neither one is a solution. Mud puddles and fog are both called suspensions, which are mixtures of bits of matter that are big enough to be seen. A mud puddle is a suspension of soil and water. Fog is a suspension of water droplets in air. The matter in most suspensions can be separated with a filter. But not fog, because it is a kind of suspension called a colloid. Colloids have very tiny particles of matter, so they can’t be filtered easily.
