What do lemonade, saltwater, and the air we breathe all have in common?
They are solutions, uniform mixtures of substances that play a role in everything from medicine to oceans to your bloodstream. In this lesson, we will break down what solutions are, how they form, what affects them, and how to measure what is inside them.
What Is a Solution?
A solution is a homogeneous mixture, a physical blend of two or more substances that looks and behaves like one.
Components of a solution:
- Solvent: the substance that does the dissolving, usually present in greater amount
- Solute: the substance that gets dissolved
Example: In saltwater, water is the solvent and salt is the solute.
Types of Solutions
Solutions can form in different states of matter:
| Type | Solute | Solvent | Example |
| Solid in liquid | Salt | Water | Saltwater |
| Gas in liquid | Carbon dioxide | Water | Soda |
| Liquid in liquid | Alcohol | Water | Rubbing alcohol |
| Solid in solid | Copper | Zinc | Brass alloy |
| Gas in gas | Oxygen | Nitrogen | Air |
Solubility: How Much Can Dissolve?
Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature and pressure.
Factors that affect solubility:
- Temperature
- Solids: usually dissolve more at higher temperatures
- Gases: dissolve less at higher temperatures (why warm soda goes flat faster)
- Pressure
- Affects gases only. Higher pressure allows more gas to dissolve (as in sealed soda cans)
- Polarity
- “Like dissolves like.” Polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes
- Example: water (polar) dissolves salt (polar) but not oil (nonpolar)
Saturation Levels
| Type of Solution | Description |
| Unsaturated | More solute can still dissolve |
| Saturated | The maximum amount of solute has dissolved |
| Supersaturated | Contains more solute than normally possible; unstable |
Example: Heating water to dissolve extra sugar and then cooling it. Crystals may form as the solution releases the extra solute.
Concentration Calculations
Concentration describes how much solute is dissolved in a given amount of solvent.
- Molarity (M):
M = moles of solute ÷ liters of solution
Example: If 2 moles of NaCl are dissolved in 1 liter of water, the solution is 2.0 M (read as “2 molar”). - Percent Concentration:
- Percent by mass = (mass of solute ÷ mass of solution) × 100%
- Percent by volume = (volume of solute ÷ volume of solution) × 100%
Example: A 70% alcohol solution means 70 mL of alcohol per 100 mL of solution.
Acids, Bases, and the pH Scale
Many solutions we encounter are acids or bases, and their strength is measured on the pH scale.
| pH Level | Type | Example |
| 0–6 | Acid | Lemon juice, vinegar |
| 7 | Neutral | Pure water |
| 8–14 | Base | Soap, baking soda |
- Acids donate hydrogen ions (H⁺)
- Bases donate hydroxide ions (OH⁻)
- Strong acids and bases ionize completely, while weak ones only partially ionize
Fun fact: stomach acid is about pH 1. Coffee is around 5. Soap is about 10.
Recap Chart
| Concept | Meaning |
| Solution | Homogeneous mixture of solute and solvent |
| Solubility | Maximum amount of solute that can dissolve |
| Molarity | Moles of solute per liter of solution |
| Saturated | Solution holding the maximum solute |
| Supersaturated | Solution with more solute than normally possible |
| pH Scale | Measures acidity or basicity on a 0–14 scale |
Thought to Take With You
Solutions are everywhere, both in chemistry and in life. Sometimes all it takes is the right mix. (guys look how wise i am oh my gawsh)
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