Calculate the pH of 0.0022 M NaOH
Use this interactive chemistry calculator to determine the pOH, pH, hydroxide concentration, and hydrogen ion concentration for a sodium hydroxide solution. For a strong base like NaOH, dissociation is essentially complete in dilute aqueous solution, so the stoichiometric hydroxide concentration is the starting point for the pH calculation.
Calculator
NaOH is treated as a strong base that dissociates completely.
Enter molarity in mol/L, such as 0.0022.
This calculator uses pH + pOH = 14.00 at 25 degrees C.
Choose how many decimals to display in the final values.
Optional label for your own lab, homework, or revision context.
Chart compares pH, pOH, hydroxide concentration, and hydrogen ion concentration on a logarithmic visual scale.
How to calculate the pH of 0.0022 M NaOH
Calculating the pH of 0.0022 M NaOH is a standard general chemistry problem that tests your understanding of strong bases, hydroxide ion concentration, logarithms, and the pH scale. Sodium hydroxide, written as NaOH, is one of the most familiar strong bases encountered in chemistry classes, analytical laboratories, industrial cleaning formulations, and process control systems. Because it is a strong base, it dissociates essentially completely in water:
NaOH(aq) → Na+(aq) + OH–(aq)
That complete dissociation is the key shortcut. If the solution concentration is 0.0022 M NaOH, then the hydroxide concentration is also 0.0022 M OH–, assuming the solution is dilute and measured at standard classroom conditions. Once you know the hydroxide concentration, you calculate pOH using the negative base-10 logarithm, then convert pOH to pH by using the 25 degrees C relationship pH + pOH = 14.
Step by step solution
- Identify NaOH as a strong base.
- Assume complete dissociation in water.
- Set hydroxide concentration equal to the NaOH molarity: [OH–] = 0.0022 M.
- Calculate pOH: pOH = -log(0.0022).
- Evaluate the logarithm: pOH ≈ 2.6576.
- Use the 25 degrees C relationship pH = 14.000 – 2.6576.
- Get the final pH: pH ≈ 11.3424.
Rounded to three decimal places, the pH of 0.0022 M NaOH is 11.342. Rounded to two decimal places, it is 11.34. This value confirms that the solution is basic, as expected for sodium hydroxide.
Why the hydroxide concentration equals the NaOH concentration
In many acid-base calculations, equilibrium expressions are needed because the solute does not ionize completely. NaOH is different. It is classified as a strong electrolyte and a strong base. In introductory and most intermediate pH problems, this means each mole of NaOH contributes one mole of OH–. Therefore:
- 0.0022 mol/L NaOH gives 0.0022 mol/L OH–
- There is a 1:1 mole ratio between NaOH and OH–
- No ICE table is required for the basic classroom calculation
This is also why sodium hydroxide calculations are often easier than weak base calculations involving ammonia or amines, where the base dissociation constant and equilibrium setup become essential.
The exact formula used
The formula sequence is simple:
- [OH–] = CNaOH
- pOH = -log10[OH–]
- pH = 14.00 – pOH
Substituting the given concentration:
pOH = -log10(0.0022) = 2.6576
pH = 14.0000 – 2.6576 = 11.3424
Scientific notation version
Some students prefer to convert 0.0022 M into scientific notation before applying the logarithm:
0.0022 = 2.2 × 10-3
Then:
pOH = -log(2.2 × 10-3) = -(log 2.2 + log 10-3) = -(0.3424 – 3) = 2.6576
This gives the same result and can help you understand how the logarithm changes when concentration changes by a factor of ten.
Comparison table: NaOH concentration vs pH at 25 degrees C
| NaOH Concentration (M) | [OH-] (M) | pOH | pH | Interpretation |
|---|---|---|---|---|
| 0.00010 | 1.0 × 10^-4 | 4.000 | 10.000 | Mildly basic |
| 0.0010 | 1.0 × 10^-3 | 3.000 | 11.000 | Clearly basic |
| 0.0022 | 2.2 × 10^-3 | 2.658 | 11.342 | Moderately basic |
| 0.0100 | 1.0 × 10^-2 | 2.000 | 12.000 | Strongly basic |
| 0.1000 | 1.0 × 10^-1 | 1.000 | 13.000 | Very strongly basic |
This table shows a key trend: every tenfold increase in hydroxide concentration lowers pOH by 1 unit and raises pH by 1 unit at 25 degrees C. Your target solution, 0.0022 M NaOH, falls between 0.0010 M and 0.0100 M, so its pH is sensibly between 11 and 12.
Comparison table: hydrogen ion and hydroxide ion concentrations
| Solution | [OH-] (M) | [H+] (M) | pOH | pH |
|---|---|---|---|---|
| Pure water at 25 degrees C | 1.0 × 10^-7 | 1.0 × 10^-7 | 7.000 | 7.000 |
| 0.0022 M NaOH | 2.2 × 10^-3 | 4.55 × 10^-12 | 2.658 | 11.342 |
| 0.0100 M NaOH | 1.0 × 10^-2 | 1.0 × 10^-12 | 2.000 | 12.000 |
Notice how small the hydrogen ion concentration becomes in a basic solution. For 0.0022 M NaOH, the hydrogen ion concentration is only about 4.55 × 10-12 M. That is why the pH is so far above neutral.
Common mistakes when solving this problem
- Using pH = -log(0.0022) directly. That would be correct only for a strong acid, not for NaOH.
- Forgetting to calculate pOH first. Since NaOH gives OH–, you find pOH before pH.
- Mixing up the formula. The correct relationship at 25 degrees C is pH + pOH = 14.00.
- Ignoring temperature assumptions. The value 14.00 is a classroom standard at 25 degrees C.
- Dropping the 1:1 stoichiometry. One mole of NaOH gives one mole of OH–.
How this relates to laboratory chemistry
In real laboratories, pH can be measured with pH electrodes, indicator papers, or colorimetric probes, but calculation remains important. A chemist preparing a dilute sodium hydroxide solution often estimates the expected pH before making the solution. This helps with quality control, titration planning, corrosion awareness, safety protocols, and compatibility with glassware, seals, and analytical instruments.
For example, if you are preparing a wash solution, regeneration bath, or titrant, knowing that 0.0022 M NaOH has a pH around 11.34 immediately tells you the solution is significantly basic but still far less concentrated than common stock NaOH solutions used in industrial settings. This distinction matters for hazard assessment and dilution planning.
Does water autoionization matter here?
For 0.0022 M NaOH, not really. Water contributes roughly 1.0 × 10-7 M OH– at 25 degrees C, which is tiny compared with 2.2 × 10-3 M from the dissolved sodium hydroxide. Since the NaOH concentration is about 22,000 times larger than the hydroxide from pure water, the water contribution is negligible for normal coursework and routine calculations.
What if the concentration were much smaller?
At very low strong-base concentrations, especially near 10-7 M, the autoionization of water becomes significant and the simplified approach becomes less accurate. But 0.0022 M is comfortably high enough that the standard strong-base shortcut is valid. In other words, this problem is exactly the kind of case where complete dissociation and pH + pOH = 14 work cleanly.
Interpreting the answer in practical terms
A pH of 11.342 indicates a basic solution that can irritate skin and eyes and should still be handled with laboratory care. It is nowhere near neutral, and it contains far more hydroxide than pure water. However, it is also much less concentrated than 1.0 M NaOH, which would have a much higher pH and significantly greater corrosive potential.
Quick mental estimation method
Since 0.0022 M equals 2.2 × 10-3 M, the exponent alone tells you pOH will be a little less than 3, because log(2.2) is positive. Therefore pOH should be about 2.66, and pH should be about 11.34. This quick estimate is a great exam technique because it lets you check whether your calculator result is reasonable.
Authoritative chemistry references
For foundational chemistry and water chemistry data, consult: U.S. Environmental Protection Agency, National Institute of Standards and Technology, and Chemistry LibreTexts.
Final answer
To calculate the pH of 0.0022 M NaOH, first recognize that NaOH is a strong base and dissociates completely, so [OH–] = 0.0022 M. Then calculate pOH using the logarithm:
pOH = -log(0.0022) ≈ 2.658
Next, convert to pH at 25 degrees C:
pH = 14.000 – 2.658 = 11.342
Therefore, the pH of 0.0022 M NaOH is approximately 11.34.