Calculate pH of Sr(OH)2
Use this interactive calculator to determine the pH, pOH, hydroxide concentration, and dissolved Sr(OH)2 molarity for strontium hydroxide solutions at 25°C, assuming ideal complete dissociation.
Results
Concentration vs pH Chart
Expert guide: how to calculate pH of Sr(OH)2 correctly
When students, lab technicians, and chemistry professionals need to calculate pH of Sr(OH)2, the key concept is that strontium hydroxide is a strong base that contributes hydroxide ions directly to solution. Unlike weak bases, which require an equilibrium expression to estimate ionization, Sr(OH)2 is treated in most introductory and intermediate chemistry problems as fully dissociated once dissolved. That dramatically simplifies the calculation. The only real challenge is remembering the stoichiometric factor: each formula unit of strontium hydroxide releases two hydroxide ions.
In water, the dissociation is written as:
Sr(OH)2(aq) → Sr2+(aq) + 2OH-(aq)
This equation tells you everything you need for a standard pH calculation at 25°C. If the molarity of dissolved Sr(OH)2 is known, then the hydroxide concentration is simply double that value. From there, you calculate pOH using a base-10 logarithm, and then convert pOH into pH by subtracting from 14. This workflow is quick, reliable, and widely used in chemistry education because it reflects the stoichiometric behavior of a strong metal hydroxide.
Fast formula for Sr(OH)2 pH
- Start with the dissolved molarity of Sr(OH)2, written as C.
- Compute hydroxide concentration: [OH-] = 2C.
- Compute pOH: pOH = -log10([OH-]).
- Compute pH at 25°C: pH = 14 – pOH.
Example: if a solution is 0.010 M Sr(OH)2, then the hydroxide concentration is 0.020 M. The pOH is -log10(0.020) = 1.699. The pH is 14 – 1.699 = 12.301. That is the correct approach because each mole of Sr(OH)2 supplies two moles of hydroxide ions.
Why the factor of 2 matters
Many pH errors come from forgetting that Sr(OH)2 contains two hydroxide groups. If you accidentally treat Sr(OH)2 like NaOH, you will underestimate the hydroxide concentration by a factor of 2. This changes pOH and causes a measurable pH error. Because the pH scale is logarithmic, even a simple stoichiometric mistake can shift the answer enough to be marked incorrect in coursework or to affect solution preparation in the lab.
For example, a 0.050 M NaOH solution has [OH-] = 0.050 M, but a 0.050 M Sr(OH)2 solution has [OH-] = 0.100 M. The second solution is significantly more basic. The difference does not come from “strength” in the acid-base sense, since both are strong bases. It comes from stoichiometry: Sr(OH)2 contributes twice as many hydroxide ions per mole of compound.
Common mistake checklist
- Using [OH-] = C instead of [OH-] = 2C for Sr(OH)2.
- Using pH = -log10[OH-] instead of pOH = -log10[OH-].
- Forgetting to convert mass to moles before dividing by volume.
- Mixing liters and milliliters.
- Ignoring that the standard relation pH + pOH = 14 is valid specifically at 25°C.
How to calculate pH of Sr(OH)2 from molarity
If your chemistry problem already gives molarity, you are one step away from the result. Suppose the concentration is 0.0020 M Sr(OH)2. First multiply by 2 to obtain hydroxide concentration:
[OH-] = 2 × 0.0020 = 0.0040 M
Then calculate pOH:
pOH = -log10(0.0040) = 2.398
Finally:
pH = 14.000 – 2.398 = 11.602
This method is direct and should be your default approach whenever the dissolved concentration is provided. The calculator above follows exactly this logic.
How to calculate pH of Sr(OH)2 from mass and volume
Sometimes a problem gives the amount of solid strontium hydroxide and the volume of solution prepared. In that case, you must convert mass to moles first. The molar mass of Sr(OH)2 is approximately 121.63 g/mol. The steps are:
- Convert mass into grams if needed.
- Calculate moles: moles = mass / 121.63.
- Convert volume into liters if needed.
- Calculate molarity: C = moles / liters.
- Then use [OH-] = 2C, followed by pOH and pH.
Suppose you dissolve 2.4326 g of Sr(OH)2 into enough water to make 500.0 mL of solution. Moles = 2.4326 / 121.63 = 0.02000 mol. Volume = 0.5000 L. So the Sr(OH)2 concentration is 0.04000 M. The hydroxide concentration is therefore 0.08000 M. Then pOH = -log10(0.08000) = 1.097, and pH = 12.903.
Comparison table: calculated pH values for common Sr(OH)2 concentrations
The table below shows real calculated values at 25°C using complete dissociation and the stoichiometric relation [OH-] = 2C. These values are useful for quick checking, estimation, and lab planning.
| Sr(OH)2 Molarity (M) | [OH-] (M) | pOH | pH at 25°C |
|---|---|---|---|
| 0.00010 | 0.00020 | 3.699 | 10.301 |
| 0.00100 | 0.00200 | 2.699 | 11.301 |
| 0.00500 | 0.01000 | 2.000 | 12.000 |
| 0.01000 | 0.02000 | 1.699 | 12.301 |
| 0.05000 | 0.10000 | 1.000 | 13.000 |
| 0.10000 | 0.20000 | 0.699 | 13.301 |
Comparison table: strong base stoichiometry and hydroxide yield
This second table helps clarify why Sr(OH)2 gives a different pH from one-hydroxide bases at the same molarity. The values shown are based on simple stoichiometric dissociation for a 0.0100 M solution of each base.
| Base | Hydroxides per formula unit | Base concentration (M) | [OH-] produced (M) | Calculated pH at 25°C |
|---|---|---|---|---|
| NaOH | 1 | 0.0100 | 0.0100 | 12.000 |
| KOH | 1 | 0.0100 | 0.0100 | 12.000 |
| Ca(OH)2 | 2 | 0.0100 | 0.0200 | 12.301 |
| Sr(OH)2 | 2 | 0.0100 | 0.0200 | 12.301 |
| Ba(OH)2 | 2 | 0.0100 | 0.0200 | 12.301 |
When ideal calculations are appropriate
In classroom chemistry and many routine calculations, treating Sr(OH)2 as fully dissociated is completely appropriate. This is especially true for moderate dilute solutions where the concentration of dissolved base is clearly given or where the problem statement implies full dissolution. In these settings, the calculation is a stoichiometric and logarithmic exercise, not an equilibrium problem.
However, in more advanced chemistry, several real-world effects can matter. Solubility limits, ionic strength, activity corrections, and temperature dependence can all shift measured pH from the ideal textbook result. If the system is very concentrated or if only a sparingly dissolved amount of Sr(OH)2 is present, then a more advanced treatment may be required. Still, for the vast majority of educational questions titled “calculate pH of Sr(OH)2,” the complete dissociation method is the expected and correct approach.
Practical interpretation of high pH values
Because Sr(OH)2 releases two hydroxide ions per mole, even modest concentrations produce strongly basic solutions. A 0.0010 M solution already has a pH of about 11.301. A 0.1000 M solution reaches about 13.301 under ideal conditions. Such values indicate corrosive, highly alkaline behavior. In practical lab settings, these solutions require eye protection, gloves, and good handling practices.
Step-by-step worked examples
Example 1: 0.0250 M Sr(OH)2
- Given: C = 0.0250 M
- [OH-] = 2 × 0.0250 = 0.0500 M
- pOH = -log10(0.0500) = 1.301
- pH = 14.000 – 1.301 = 12.699
Example 2: 500 mg in 250 mL
- Mass = 500 mg = 0.500 g
- Moles = 0.500 / 121.63 = 0.00411 mol
- Volume = 250 mL = 0.250 L
- C = 0.00411 / 0.250 = 0.01644 M
- [OH-] = 2 × 0.01644 = 0.03288 M
- pOH = -log10(0.03288) = 1.483
- pH = 14.000 – 1.483 = 12.517
How this calculator works
The calculator above automates the exact sequence used in standard chemistry. If you choose known molarity, it converts the entered unit into molarity, doubles that value to get hydroxide concentration, computes pOH with a logarithm, and then computes pH. If you choose mass and volume, it first calculates moles from the molar mass of strontium hydroxide, derives molarity by dividing by liters of solution, and then proceeds with the same hydroxide and pH calculations.
It also generates a chart that places your current solution in context by comparing your calculated pH against nearby Sr(OH)2 concentrations. This makes the logarithmic nature of pH easier to visualize and helps users understand why each tenfold concentration change does not create a linear pH jump.
Authoritative references for chemistry and pH fundamentals
For additional verification and deeper study, review these high-quality educational and government resources:
- LibreTexts Chemistry for strong base dissociation, pH, and pOH explanations.
- U.S. Environmental Protection Agency for water chemistry, pH background, and safety context.
- NCBI Bookshelf for broader scientific reference material related to chemical properties and laboratory handling.
Final takeaway
If you need to calculate pH of Sr(OH)2, remember one essential idea: double the molarity to get hydroxide concentration. Then apply the standard base formulas. At 25°C, the complete pathway is [OH-] = 2C, pOH = -log10[OH-], and pH = 14 – pOH. If you begin from mass and volume, first convert to molarity using the molar mass 121.63 g/mol. That is the reliable framework used in chemistry classes, routine solution preparation, and quick technical checks.