The pH scale shows how acidic or basic a chemical is in aqueous solution (mixed with water). The scale runs from 0 (most acidic) to 14 (most alkaline or basic), where 7 is neutral pH. Chemicals with pH values from 0 up to 7 are acids, those with a pH value of 7 are neutral, and those with pH values greater than 7 up to 14 are bases. Here is a table of pH values of common chemicals.
pH Values of Common Chemicals
|0||Hydrochloric acid (muriatic acid) – HCl|
|1.0||Stomach acid, battery acid (sulfuric acid)|
|2.2||Vinegar (Acetic acid)|
|7.4||Human tears, human blood|
|8.3||Baking soda (Sodium bicarbonate)|
|10.5||Milk of magnesia, Dead Sea|
|11.5-14.0||Hair straightening chemicals|
|12.4||Lime (calcium hydroxide)|
|14.0||Drain cleaner (sodium hydroxide)|
You’ll see charts that give slightly different pH values for some chemicals. There’s usually a pH range for a substance. For example, fruit acidity depends on soil, temperature, ripeness, and other factors. The pH of a soap depends on other ingredients in its formula. Soil pH ranges anywhere from 3 to 10. So, don’t get too caught up in the numbers.
Acids include chemicals with the word “acid” in their name. Examples include hydrochloric acid, acetic acid, and hyaluronic acid. Most fruits and vegetables are acidic. So is human skin and hair, which has a low pH to help protect the body from pathogens. Coffee, tea, wine, and milk are all acidic. Stomach acid is, of course, acidic.
Pure water is neutral. However, tap water may be slightly acidic or basic. Dissolving table salt in water does not change its pH, so ordinary salt water is neutral. Sea water is alkaline and not neutral. Fresh milk is nearly neutral, but it becomes more acidic as it sours. Vegetable oil (which is not an aqueous solution) typically registers as neutral with litmus paper.
Human blood is slightly alkaline. Baking soda (sodium bicarbonate) and washing soda (sodium carbonate) are bases. Cleaners are bases, including soap, detergent, bleach, ammonia, and drain cleaner.
What Is pH?
The numbers of the pH scale come from a formula for the hydrogen ion (H+) concentration. The equation for pH is:
pH = -log[H+]
The way a logarithmic scale works, chemicals that donate more hydrogen ions (protons) have lower pH values. These are acids. Chemicals that accept hydrogen ions have higher pH values and are bases. Because bases don’t have free hydrogen ions, it’s sometimes easier to calculate pOH. pOH is a measure of the hydroxide ion (OH–) concentration.
pOH = -log[OH–]
pH and pOH are related. At room temperature:
pH + pOH = 14
How to Measure pH
There are several ways to measure pH.
- In a lab, you’d use a pH meter for the most sensitive readings. However, pH meters are expensive and require calibration.
- Universal indicator is a liquid mixture displays a rainbow of colors. Adding a drop of a sample to a spot of universal indicator turns it a color that corresponds to a pH range. Other indicators are used for more accurate readings within narrow pH ranges.
- For home or school, pH paper test strips are a good option. Litmus paper turns red, purple, or blue to roughly estimate pH values. You’d don’t have to buy litmus paper, though. It’s easy to make homemade pH paper test strips using cabbage juice or another natural pH indicator.
- Myers, Rollie J. (2010). “One-Hundred Years of pH”. Journal of Chemical Education. 87 (1): 30–32. doi:10.1021/ed800002c
- Slessarev, E. W.; Lin, Y.; Bingham, N. L.; Johnson, J. E.; Dai, Y.; Schimel, J. P.; Chadwick, O. A. (November 2016). “Water balance creates a threshold in soil pH at the global scale”. Nature. 540 (7634): 567–569. doi:10.1038/nature20139