In chemistry, the pH scale is used to measure the acidity or basicity of a solution. The scale ranges from 0 to 14, with 7 being neutral (neither acidic nor basic). Solutions with a pH below 7 are considered acidic, while those with a pH above 7 are basic. The pH scale is logarithmic, meaning that each whole number change in the scale represents a tenfold change in acidity or basicity. For example, a solution with a pH of 3 is 10 times more acidic than a solution with a pH of 4. Common substances and their pH levels include: - Battery acid: pH 0 - Lemon juice: pH 2 - Pure water: pH 7 - Baking soda: pH 9 - Ammonia: pH 11 Understanding the pH scale is important in various fields such as environmental science, agriculture, and medicine. For example, maintaining the pH balance of soil is crucial for plant growth, and monitoring pH levels in the human body can help diagnose and treat certain medical conditions. In conclusion, the pH scale is a fundamental concept in chemistry that helps us understand the properties of different substances based on their acidity or basicity.