pH Calculator
Convert between pH, pOH, $[H^+]$, and $[OH^-]$ instantly.
pH Scale
The Ruler of Chemistry
pH is more than just a number on a test strip. It is the master variable that controls biological life, industrial corrosion, and the taste of your food.
The Mathematics
The "p" in pH stands for the negative logarithm. It turns tiny, complicated decimal numbers into simple, readable integers.
The Power of 10
Never underestimate a single pH unit.
- 1 UnitDifference between pH 6 and pH 7 is 10x the acidity.
- 2 UnitsDifference between pH 5 and pH 7 is 100x the acidity.
- 6 UnitsStomach acid (pH 1) is 1,000,000x more acidic than water (pH 7).
Common pH Values
| Substance | Approximate pH | Nature |
|---|---|---|
| Battery Acid | 0.0 | Strong Acid |
| Lemon Juice | 2.0 | Acidic |
| Coffee | 5.0 | Acidic |
| Pure Water | 7.0 | Neutral |
| Baking Soda | 9.0 | Basic |
| Bleach | 13.0 | Strong Base |
Batteries
Lead-acid batteries rely on Sulfuric Acid (pH ~0.8). The extreme acidity allows for rapid electron flow, generating the high current needed to start a car engine.
Food Preservation
Pickling works by lowering the pH below 4.6. Most dangerous bacteria (like botulism) cannot survive in this acidic environment, keeping the food safe for years.
Swimming Pools
High pH (above 7.8) makes chlorine ineffective and causes scaling. Low pH (below 7.2) corrodes pipes and irritates eyes. Keeping it between 7.2-7.6 is a delicate art.
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Frequently Asked Questions
What is pH?
pH stands for 'potential of Hydrogen'. It is a logarithmic measure of the hydrogen ion concentration [H+] in a solution. It tells you how acidic or basic a water-based liquid is on a scale of 0 to 14.
What is the formula for pH?
The definition is pH = -log[H+]. This means pH is the negative logarithm (base 10) of the molar concentration of dissolved hydrogen ions.
How do I calculate [H+] from pH?
To reverse the calculation, use the formula [H+] = 10-pH. For example, if pH is 5, the [H+] is 0.00001 M.
What is pOH?
pOH is the 'potential of Hydroxide'. It measures basicity using the concentration of OH- ions. The relationship is simple: pH + pOH = 14.
Why is the scale 0-14?
This range covers the vast majority of solutions found in nature and chemistry. However, it is possible for extremely strong acids to have negative pH (below 0) and strong bases to exceed 14.
What is neutral pH?
A pH of 7 is neutral. This is because pure water splits into equal amounts of H+ and OH- (10-7 M each). When they are balanced, the solution is neither acidic nor basic.
How do I enter scientific notation?
You can use 'e' notation. For example, to enter 1.5 × 10-5, type 1.5e-5.
Why is pH logarithmic?
Because acidity varies by huge amounts. A solution with pH 1 has 1,000,000 times more H+ ions than a solution with pH 7. Logarithms shrink these giant numbers into a simple 0-14 scale.
Does adding water change pH?
Yes. Diluting an acid makes it less acidic (pH rises toward 7). Diluting a base makes it less basic (pH falls toward 7). You cannot cross the neutral line (7) just by adding water.
How is pH measured?
Roughly with litmus paper (which changes color) or precisely with an electronic pH meter (which measures voltage potential between electrodes).
What is the pH of blood?
Human blood is slightly basic, strictly maintained between 7.35 and 7.45. If it drops below 6.8 or rises above 7.8, it can be fatal.
Can I drink water with high pH?
Alkaline water (pH 8-9) is popular but scientifically has little effect on your body's pH, which is tightly regulated by your kidneys and lungs.
What is Acid Rain?
Normal rain is slightly acidic (pH 5.6) due to CO2. 'Acid Rain' has a pH below 5.0, usually caused by industrial pollutants like Sulfur Dioxide (SO2) reacting with clouds.
Why is pH important for plants?
Soil pH determines which nutrients are available. If soil is too acidic or basic, roots physically cannot absorb certain minerals (like Iron or Phosphorus), causing the plant to starve.
What causes Heartburn?
Heartburn is acid reflux. Your stomach contains Hydrochloric Acid (pH 1.5-3.5). If this strong acid splashes up into your esophagus (which isn't protected by mucus), it burns.