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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 is sweet. But you can’t see the sugar. Why not? Because the sugar is completely dissolved in the liquid.
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 stuff that dissolves in a solvent. The solvent is often a liquid, like water. Say a solution consists of different amounts of two liquids. The solvent is the liquid that there’s more of.
▲ Here’s a good way to make lemonade: mix together lemon juice, water, and sugar.
The Lemony Ticket
Lemonade is like many other solutions.
Once it is completely mixed, a solution is the same throughout. In lemonade, the amounts of sugar, water, and lemon juice are 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? Imagine a box that’s one foot high, one foot wide, and one foot deep. Now fill it with water. That’s a cubic foot of water. 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 create freshwater from ocean water. They use evaporation and other methods. The process is called desalination. It is important in places where freshwater is hard to find.
Oil
Sand
Pepper
Wood
▲ Sugar and salt form solutions with water easily. But oil, pepper, sand, and wood do not. Why? It has to do with molecules, and the forces that hold them together. What’s a molecule? It’s the very smallest amount of something. For a solution to form, there must be an attraction between the molecules of the solute and 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. The result is 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. What do you think happens then? It rains, of course!
Fog
Mud
▲ Mud puddles and fog are mixtures, but neither is a solution. Mud puddles and fog are suspensions. A suspension is a mixture 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. Fog is a kind of suspension called a colloid. Colloids have very tiny particles of matter. As a result, they can’t be filtered easily.
