Some pH levels of common substances include a pH of 7.0 for pure water, a pH of 2.0 for lemon juice and a pH of 11.0 for ammonia. Human blood has a pH of 7.4, tomatoes have a pH of 6.6, and vinegar has a pH of 2.2.
Because vinegar, tomatoes and lemon juice all have pH levels below 7.0, they are considered acids. Milk, which has a pH of 6.6, is also considered an acid. Wine, beer and apples are also acidic. Common substances with even higher acidity include battery acid, which has a pH of 1.0, and hydrochloric acid, which has a pH of 0.
Substances with a pH above 7.0 such as ammonia and human blood are considered bases. Some other common bases are baking soda, which has a pH of 8.3 and milk of magnesia, which has a pH of 10.5. Highly basic substances include lye, which has a pH of 13.0, and sodium hydroxide, which has a pH of 14.0.
Because pure water has a pH of 7.0, it is considered a neutral substance. Acids and bases neutralize each other when combined, so mixing an acid and a base causes the pH of the combined solution to move toward a neutral pH level of 7.0.