pH Scale Table
| Substance | Approx pH | Substance | Approx pH |
|---|---|---|---|
| Drain cleaner | 13.5 | Pure water | 7.0 |
| Bleach | 12.5 | Milk | 6.7 |
| Ammonia | 11.5 | Coffee | 5.0 |
| Baking soda | 9.0 | Tomato juice | 4.5 |
| Seawater | 8.1 | Vinegar | 3.0 |
| Blood | 7.4 | Lemon juice | 2.2 |
The pH scale runs from 0 to 14 and grades how acidic or basic a water-based solution is: below 7 is acidic, 7 is neutral, above 7 is basic. Each step is a factor of ten - lemon juice at pH 2 is ten times more acidic than vinegar at 3 and a hundred thousand times more than pure water at 7. Type a pH and the converter reads back the class, the hydrogen-ion concentration in moles per liter, and the matching pOH.
The table places the everyday substances people actually ask about, from the extremes (battery acid at one end, drain cleaner at the other) to the narrow middle band where biology lives: blood holds near 7.4, skin sits slightly acidic near 5.5, and unpolluted rain is naturally mildly acidic around 5.6 because dissolved carbon dioxide makes weak carbonic acid - rain below about 5.0 is what the EPA counts as acid rain.
How to use
- Type a pH between 0 and 14 - the class, hydrogen-ion concentration and pOH update instantly.
- Read concentration in scientific notation: each pH step moves the decimal one place, so pH 4 is 10 times as concentrated in H+ as pH 5.
- Compare against the table's anchors, not the bare number: pH 6.5 sounds neutral but is four times the acidity of milk.
Frequently asked questions
Why does the pH scale stop at 14?
It doesn't, quite - the 0-to-14 range covers ordinary aqueous chemistry because water ionizes such that neutral is 7 at room temperature and strongly concentrated acids and bases land at the ends. Concentrated solutions can measure below 0 or above 14 in the lab, but household and environmental chemistry stays inside the classic ladder, which is why textbooks and the EPA chart draw it 0 to 14.
What pH is safe for skin and eyes?
Skin prefers slightly acidic, near pH 4.5 to 5.5, matching its acid mantle that discourages bacteria; eye moisture sits near 7.4. That is why harsh soaps sting - they are basic around 9 to 10 - and why pool operators hold water between 7.2 and 7.8: comfortable for swimmers and effective for chlorine at the same time.
Is pH logarithmic?
Yes - pH is the negative base-ten logarithm of hydrogen-ion concentration in moles per liter. One pH step equals a tenfold change in acidity, so the distance from lemon juice (2) to coffee (5) is not 3 units but a thousand-fold difference in H+ concentration. The pOH number mirrors it for hydroxide ions, and the two always sum to about 14 in water.
What pH is acid rain?
Normal rain is already mildly acidic near pH 5.6 from dissolved carbon dioxide; the EPA treats rain below about 5.0 as acid rain, where sulfur dioxide and nitrogen oxides from combustion form sulfuric and nitric acid. Streams and lakes differ naturally too - most surface water sits between 6.5 and 8.5, and the USGS notes aquatic life gets stressed outside roughly 6 to 9.
Which common substances sit in the middle of the scale?
Milk near 6.7, human blood held tightly near 7.4, and seawater around 8.1. The middle of the scale is where chemistry is alive: blood drifting just 0.3 toward acidic is a medical emergency, seawater has slipped about 0.1 since industrialization - a roughly thirty percent rise in hydrogen ions - and pool test kits resolve half-steps for exactly this sensitivity.