Calculate pH for 1.7 × 10-3 M Sr(OH)2
Use this interactive calculator to determine hydroxide concentration, pOH, and final pH for strontium hydroxide solutions. The default values are set for 1.7 × 10-3 M Sr(OH)2 at 25°C.
Sr(OH)2 pH Calculator
Results
Enter or confirm the values above, then click Calculate pH.
How to calculate pH for 1.7 × 10-3 M Sr(OH)2
If you need to calculate pH for 1.7 10 3 m sr oh 2, the chemistry is straightforward once you recognize that strontium hydroxide is a strong base. In water, Sr(OH)2 dissociates essentially completely into one strontium ion and two hydroxide ions. That detail matters because pH is not determined directly from the formal concentration of the base. Instead, you first find the resulting hydroxide ion concentration, then calculate pOH, and finally convert pOH to pH.
For the default problem, the concentration is 1.7 × 10-3 M. Since each formula unit of strontium hydroxide contributes 2 OH–, the hydroxide concentration becomes:
- Start with the base concentration: 1.7 × 10-3 M
- Multiply by 2 because Sr(OH)2 releases two hydroxide ions
- Compute [OH–] = 3.4 × 10-3 M
- Use pOH = -log[OH–]
- Then use pH = 14.00 – pOH at 25°C
When you carry out the math, pOH is approximately 2.47, which means the pH is approximately 11.53. That result makes sense chemically. A solution with millimolar hydroxide concentration should be clearly basic, and a pH above 11 is entirely consistent with a strong metal hydroxide in that range.
Step by step solution
The balanced dissociation equation is:
Sr(OH)2(aq) → Sr2+(aq) + 2OH–(aq)
Because the stoichiometric coefficient in front of hydroxide is 2, the hydroxide concentration is:
[OH–] = 2 × 1.7 × 10-3 = 3.4 × 10-3 M
Next:
pOH = -log(3.4 × 10-3) ≈ 2.4685
Finally, at 25°C:
pH = 14.0000 – 2.4685 = 11.5315
Rounded appropriately, the answer is pH ≈ 11.53.
Why the factor of 2 is essential
One of the most common mistakes in pH problems involving bases such as calcium hydroxide, barium hydroxide, and strontium hydroxide is forgetting the number of hydroxide ions produced by each unit of the compound. If you used 1.7 × 10-3 M directly as [OH–], you would underestimate the basicity of the solution. In acid-base stoichiometry, that coefficient is not optional. It is the entire reason why the final pH is higher than the value you would get from a simple one-to-one base.
- NaOH releases 1 hydroxide ion per formula unit
- KOH releases 1 hydroxide ion per formula unit
- Sr(OH)2 releases 2 hydroxide ions per formula unit
- Ba(OH)2 releases 2 hydroxide ions per formula unit
That means equal formal molar concentrations of NaOH and Sr(OH)2 do not produce equal hydroxide concentrations. For strong bases, the ion count directly changes the pOH and therefore the pH.
Comparison table: strong base stoichiometry and resulting pH
| Base | Formal concentration | OH– ions released | [OH–] produced | pOH at 25°C | pH at 25°C |
|---|---|---|---|---|---|
| NaOH | 1.7 × 10-3 M | 1 | 1.7 × 10-3 M | 2.77 | 11.23 |
| Sr(OH)2 | 1.7 × 10-3 M | 2 | 3.4 × 10-3 M | 2.47 | 11.53 |
| Ba(OH)2 | 1.7 × 10-3 M | 2 | 3.4 × 10-3 M | 2.47 | 11.53 |
This table shows the practical effect of dissociation stoichiometry. At the same initial concentration, a divalent hydroxide such as strontium hydroxide produces about twice the hydroxide ion concentration of a monovalent hydroxide like sodium hydroxide. Because pH is logarithmic, doubling [OH–] does not double the pH, but it does shift the result significantly.
Scientific notation and how to read the problem correctly
The phrase 1.7 10 3 m sr oh 2 is usually shorthand for 1.7 × 10-3 M Sr(OH)2. In chemistry, concentration values are often written in scientific notation to keep the numbers compact and clear. Here:
- 1.7 is the coefficient
- 10-3 indicates the decimal shift
- M means molarity, or moles per liter
- Sr(OH)2 is strontium hydroxide
Converting 1.7 × 10-3 to decimal form gives 0.0017 M. Since the compound releases two hydroxide ions, the hydroxide concentration becomes 0.0034 M.
What the pH value means in practice
A pH of 11.53 indicates a strongly basic solution. On the common pH scale, values above 7 are basic, values below 7 are acidic, and 7 is neutral at 25°C. However, the scale is logarithmic, so every single pH unit corresponds to a tenfold change in hydrogen ion activity. That means a solution at pH 11.53 is not just slightly basic. It is far more basic than neutral water.
In many educational contexts, solutions above pH 11 are treated as noticeably caustic and should be handled with appropriate laboratory precautions. Even when a problem is purely numerical, it is useful to connect the answer back to the chemistry: strong hydroxide concentration means strong basicity, and that matches the calculated result.
Common mistakes students make
- Forgetting the 2 in Sr(OH)2. This is the most frequent error.
- Using pH = -log[OH–]. That equation gives pOH, not pH.
- Dropping the negative exponent. 10-3 is 0.001, not 1000.
- Ignoring temperature assumptions. The relation pH + pOH = 14 is standard at 25°C.
- Rounding too early. Keep extra digits until the last step.
If you avoid these mistakes, the problem becomes routine. Strong base problems with complete dissociation are among the cleaner acid-base calculations in introductory chemistry.
Data table: pH values for several Sr(OH)2 concentrations
| Sr(OH)2 concentration | Resulting [OH–] | pOH | pH | Interpretation |
|---|---|---|---|---|
| 1.0 × 10-4 M | 2.0 × 10-4 M | 3.70 | 10.30 | Clearly basic |
| 1.0 × 10-3 M | 2.0 × 10-3 M | 2.70 | 11.30 | Strongly basic |
| 1.7 × 10-3 M | 3.4 × 10-3 M | 2.47 | 11.53 | Strongly basic |
| 1.0 × 10-2 M | 2.0 × 10-2 M | 1.70 | 12.30 | Very strongly basic |
These values are generated from the same stoichiometric logic used in the calculator above. They show a reliable trend: as the concentration of Sr(OH)2 increases by a factor of ten, pOH drops by about one unit and pH rises by about one unit. The logarithmic nature of pH creates this clean pattern.
Conceptual shortcut for strong hydroxides
Once you are comfortable with the chemistry, you can use a fast mental framework:
- Identify whether the base is strong
- Count how many OH– ions each formula unit releases
- Multiply the formal molarity by that number
- Take the negative log to get pOH
- Subtract from 14 at 25°C
In this case:
- Strong base: yes
- OH– per formula unit: 2
- [OH–] = 2 × 1.7 × 10-3
- pOH = 2.47
- pH = 11.53
How this connects to broader acid-base chemistry
The reason pH calculations are so central in chemistry is that acidity and basicity influence reaction rates, equilibrium, solubility, corrosion, biological compatibility, and environmental quality. Even though this problem is textbook style, the same principles appear in water treatment, industrial cleaning, analytical chemistry, and laboratory synthesis. Hydroxide concentration is especially important because many metal ions precipitate at elevated pH, and many materials degrade in strongly basic environments.
If you want a broader scientific context for pH and aqueous chemistry, authoritative resources from major public institutions are useful starting points. The USGS Water Science School explains how pH works in natural waters. The U.S. Environmental Protection Agency discusses environmental effects of pH. For foundational instructional chemistry, the University of Wisconsin chemistry materials provide a clear introduction to acid-base relationships.
Final answer
For 1.7 × 10-3 M Sr(OH)2:
- [OH–] = 3.4 × 10-3 M
- pOH ≈ 2.47
- pH ≈ 11.53
That is the correct result under the usual assumption of complete dissociation and the standard 25°C relationship pH + pOH = 14. Use the calculator above to verify the number, experiment with other concentrations, or compare how the pH changes when a base releases different numbers of hydroxide ions.