A pH less than 7 indicates acidity. The pH scale ranges from 0 to 14, with 7 being neutral. Solutions with a pH below 7 are considered acidic, while those above 7 are alkaline (basic). The lower the pH value, the stronger the acid.
Understanding the pH Scale
The pH scale is a logarithmic scale that measures the concentration of hydrogen ions (H⁺) in a solution. As mentioned in multiple sources, including the US EPA (https://www.epa.gov/goldkingmine/what-ph), the USGS (https://www.usgs.gov/media/images/ph-scale-0), and the Merck Manual (https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/acid-base-balance/overview-of-acid-base-balance), a pH of 7 is neutral. Values below 7 represent increasing acidity, with 0 being the most acidic.
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Examples of acidic substances: Lemon juice (pH around 2), vinegar (pH around 3), stomach acid (pH around 1.5-3.5). Even clean rain is slightly acidic, with a pH between 5.0 and 5.5, as noted by the EPA (https://www3.epa.gov/acidrain/education/site_students/phscale.html).
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Practical implications: Understanding pH is crucial in many fields, including chemistry, biology, environmental science, and food science. For instance, the pH of soil affects plant growth, and the pH of water influences aquatic life. In medicine, pH levels are vital for diagnosing conditions like acid reflux (as seen in the MedlinePlus explanation of esophageal pH tests https://medlineplus.gov/lab-tests/esophageal-ph-test/).
Acidity and Hydrogen Ions
Khan Academy (https://www.khanacademy.org/science/biology/water-acids-and-bases/acids-bases-and-ph/a/acids-bases-ph-and-bufffers) explains that acidic solutions have a higher concentration of hydrogen ions (H⁺) than pure water. This high concentration is what gives acids their characteristic properties.
