This free online tool will make it easy to check the pH or ion concentration of a solution. Just enter your data and get instant results for pH, pOH, [H⁺], and [OH⁻].
pH Calculator
Calculate pH, pOH, [H+], and [OH-] concentrations
Features of pOH calculator
ChemicalTweak tool offers Multiple Calculation Methods
- Calculate from H+/OH- ion concentrations
- Work directly with common acids and bases (HCl, NaOH, CH₃COOH, NH₃, etc.)
- Convert between pH and pOH values
- Handle both strong and weak acids/bases with proper equilibrium calculations
To calculate pH or concentration, you can determine the number of moles from mass with our Grams to Moles Calculator
How to Use This Calculator
Method 1: From Acid/Base Solutions
- Select your substance type (Strong Acid, Weak Acid, Strong Base, Weak Base)
- Choose the specific chemical from the dropdown (shows Ka/Kb values automatically)
- Enter concentration and units
- Hit Calculate
Example: For 0.1 M acetic acid solution, select “Weak Acid” → “Acetic acid” → enter “0.1” → select “M”
Method 2: From Ion Concentrations
- Choose H+ or OH- ions
- Enter concentration with appropriate units (M, mM, μM, nM)
- Calculate to get all related values
Method 3: From Known pH/pOH Simply enter the known pH or pOH value to calculate concentrations.
Calculation :
During equipment cleaning, a chemical plant generates wastewater containing 0.001 M hydrochloric acid (HCl). Before discharge, the effluent must be neutralized to pH ≈ 7 to meet environmental standards. Determine the pH of the wastewater and the amount of NaOH required to neutralize 1 m³ (1000 L) of this wastewater.
Step 1: Calculate pH
[H+]=0.001 M
pH=−log10(0.001)=3.00
The wastewater is acidic with a pH of 3.0.
Step 2: Calculate NaOH required for neutralization
HCl + NaOH → NaCl + H2O
For 1 m³ (1000 L) of wastewater:
n(HCl) = 0.001 × 1000 = 1.0
m(NaOH) = 1.0 × 40.0 = 40.0 g
✅ Result: 40 g of NaOH (or approximately 0.4 L of 10% NaOH solution) is needed to neutralize 1 m³ of wastewater to near-neutral pH.
FAQ
1. How to convert molarity to pH?
The Formula to calculate for strong acids, pH = log₁₀(molarity) and for strong bases, pOH = –log₁₀(molarity), then pH = 14 – pOH. For weak acids and bases, you can’t use a direct formula because they don’t fully dissociate. We can use the acid (Ka) or base (Kb) dissociation constant to find [H⁺] or [OH⁻]. Then, calculate pH: pH = –log₁₀[H⁺]
2. How to calculate pH?
There are a number of online tools available which can help you to calculate pH, such as ChemicalTweak online pH calculator
