Science · Solutions & reactions
Acids, Bases, and pH
Estimated time includes reading and one quiz. Take the time you need.
Start here: key ideas
- Acids increase hydrogen ion concentration in water.
- Bases decrease hydrogen ion concentration or increase hydroxide ions.
- A lower pH is more acidic; a higher pH is more basic.
- Each pH unit represents a tenfold change in hydrogen ion concentration.
- Neutralization combines acid and base effects.
- Buffers resist sudden pH change.
What you’ll be able to do
- Recognize acids and bases.
- Interpret the direction and tenfold steps of pH.
- Explain neutralization.
- Explain how a buffer limits pH change.
Compare acids and bases, read the pH scale, and explain neutralization and buffers.
Optional review
If you’d like to review the basics, visit Solutions, Concentration, and Solubility. You can start this lesson without completing those first.
Recognizing acids and bases
An acid increases hydrogen ion, H+, concentration in water. A base accepts H+ or increases hydroxide ion, OH−, concentration.
In water, H+ is carried as hydronium, H3O+. An acid can donate H+ and a base can accept H+. H+ is also called a proton; use the transfer of H+, rather than the name of a definition, to identify the roles.
Indicators change color over certain pH ranges. Strong and weak describe how fully an acid or base reacts in water. Concentrated and dilute describe amount, so these word pairs are not the same.
Acids often taste sour and react with some metals, while bases often feel slippery, but never identify lab chemicals by touching or tasting them. Use indicators or measurements. A strong acid may be dilute, and a weak acid may be concentrated.
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