Understanding Acids
Acids are substances that can donate protons (H+) in a solution, and they usually have a sour taste. Let's evaluate the substances listed: seawater, tap water, lime juice, and human saliva.
Seawater
- Seawater is primarily composed of water and various dissolved salts.
- It has a slightly alkaline pH, generally around 7.5 to 8.0, making it not an acid.
Tap Water
- Tap water is typically neutral with a pH close to 7.
- While it may contain small amounts of dissolved minerals, it is not acidic.
Lime Juice
- Lime juice is known for its sour taste due to citric acid.
- It has a pH of about 2 to 3, categorizing it clearly as an acid.
Human Saliva
- Human saliva is slightly acidic to neutral, with a pH that can range from 6.2 to 7.6.
- It contains enzymes and other substances, but it is not predominantly acidic like lime juice.
Conclusion
Among the listed substances, lime juice is the only one that qualifies as an acid due to its low pH and the presence of citric acid. Understanding the nature of these substances helps in identifying their properties and applications in daily life.