A pH (potential hydrogen or potential of hydrogen ion) scale is an indicator that helps determine hydrogen ion concentration levels in a liquid. In other words, a pH scale helps ascertain a solution’s acidity or alkalinity levels. Founded in 1909 by a Danish chemist, Soren Sorensen, the pH scale’s value range is pH 0 to pH 14. The pH number is lower when hydrogen ions in a liquid are higher, and vice-versa. The lower the number on the pH scale, the more acidic is the liquid. Higher numbers represent strong alkalis.

A liquid with a 7 pH scale is neutral, meaning it’s neither an acid nor an alkali. If the number ranges between 1 and 6 on the scale, it’s an acid. And, if the figure falls in the 8 to 14 range, it’s an alkali. Water has a pH value of 7. Some acidic liquids are digestive juices with a pH level of 1, lemon juice with pH 3, and acid rain with pH 5. Human blood, liquid soaps, household cleaners, etc. are alkalis and have pH values above 7.

Testing & Interpreting Values

A universal indicator paper, which is also known as litmus paper, is generally used to test a liquid’s pH level. It’s dipped into the solution to be tested. The indicator changes color when it interacts with the solution. The color red represents pH 1, whereas green/yellow signifies pH 7. Different shades of blue represent higher pH values. Every specific pH number is denoted by a particular hue. In quite a few pH scales, the difference is denoted by a lighter or darker shade of the same color. Basically, there are no standard pH scale colors.

In numerical terms, the difference between the values on a pH scale is 1 (+/-). However, each value is ten times stronger or weaker than the numbers preceding and succeeding. For instance, the value 9 is ten times more acidic than 10 and ten times less acidic than 8. This means the value 8 is 100 times more acidic than 10 (10*10). According to some scientists, a liquid cannot be neutral. It should be either acid or alkaline. It’s therefore believed water or any liquid with a pH of 7 is an extremely weak base or acid.

Though the pH scale values are 0 to 14, these values don’t represent the maximum a liquid can go as far as being an acid or alkali. In other words, these numbers are not absolute and some liquids can be more of an acid than what pH 0 or pH 1 suggests or more of an alkali than what pH 14 indicates. This is because there is realistically no upper or lower limit to how many hydrogen ions there could be in a liquid. But since the majority of liquids tend to fall in this range, the pH scale is widely used.

Also, the pH value of a particular liquid may vary with temperature. For example, water at room temperature has a pH of 7. However, at 100 degree Celsius, the pH number could come down to 6.14. And at 0 degree Celsius, the pH value could touch 7.47. These fluctuations do not mean water is becoming alkaline or acidic. Those numbers are, in fact, the neutral point for water at the respective temperatures.  

Why Find Out pH Values?

There is nothing such as a “good” pH level. Certain substances are naturally designed to be acidic and others basic. The recommended pH for stomach acid is 1. Freshwater community aquariums’ pH values should be within 6.5 and 7.5. This is because most freshwater fishes are more comfortable in water that’s neutral or marginally acidic or basic. Water conditioners can be used to keep the water’s pH under control. The pH scale is also used by chemists and doctors to determine how neutral, sour (acid) or sweet (alkaline) a substance is.   

A heartburn could have been due to acid presence in the stomach. In such cases, a base such as antacid is administered to neutralize the extra acid. The pH value of blood is marginally basic. An alteration in the blood’s pH could seriously harm the body’s vital organs. Some diseases can be diagnosed only after checking urine and blood pH values. In agriculture, some crops grow better at a specific pH range. The enzyme activation in the human body also happens at a particular pH.