All About Solutions

Lesson Plan - Get It!

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What Is a Solution?

A solution is a type of homogeneous mixture in which one substance (the solute) dissolves evenly into another (the solvent).

These mixtures appear uniform throughout—you can’t see the parts, even under a microscope. Sugar water, saltwater, and soda are all solutions.

Solutions can exist in any phase: solid, liquid, or gas. Here are examples.

Steel is a solid solution of carbon in iron.

Carbonated drinks are gas dissolved in liquid.

Vinegar is a liquid solution of acetic acid in water.

Water is often called the universal solvent because it dissolves more substances than any other liquid—but that doesn’t mean it can dissolve everything.

What Determines Whether Something Dissolves?

Polarity: “Like Dissolves Like”

The key to understanding solubility is the concept of polarity. A substance’s polarity refers to the way electrons are shared in its molecules.

Polar molecules (like water) have uneven charge distribution.

Non-polar molecules (like oil) share electrons evenly.

A polar solute dissolves best in a polar solvent, and a non-polar solute dissolves best in a non-polar solvent.

That’s why oil and water don’t mix, but dish soap (which has both polar and non-polar parts) can help bridge the gap.

To explain this, imagine a molecular tug-of-war.

If two identical “wrestlers” (atoms with the same pull on electrons) are pulling from either side—like in carbon dioxide (CO?)—the molecule is non-polar overall. The pulls cancel out.

In a molecule like water (H?O), the tug-of-war isn’t even. Oxygen has more “pull” (electronegativity) and also holds onto lone pairs—unbonded electrons—giving it extra power. The result? An uneven distribution of charge. That’s what makes water polar and so good at dissolving other polar substances.

Factors That Affect Solubility

Solubility doesn’t just depend on polarity—it’s influenced by other factors, too.

Temperature

Solids (like sugar) dissolve faster in warm liquids.

Gases (like CO? in soda) dissolve better in cold liquids.

Pressure

Increasing pressure increases the solubility of gases in liquids. (That’s how carbonated drinks are bottled.)

Particle Size

Smaller particles dissolve faster—powdered sugar beats sugar cubes.

Mechanical Motion

Stirring, shaking, or swirling a mixture speeds up dissolving by increasing particle interaction.

How Solubility Works in Real Life

Sugar in tea: The sugar is the solute, tea is the solvent. Stirring helps it dissolve faster.

Dish soap vs. grease: Water alone can’t remove grease because they’re polar vs. non-polar. Dish soap works because it has both polar and non-polar ends, which trap grease and wash it away.

Soda: Carbon dioxide gas is forced into liquid under high pressure. Once opened, the pressure drops and the gas escapes—hence the fizz.

You’ve learned what makes a solution, what affects how substances dissolve, and why some things won’t mix.

Now, see how well you can sort through the science with a few quick checks and some hands-on discovery in the Got It? section.