Calculate pH for 2.0 × 10-3 M Sr(OH)2
Use this premium calculator to determine hydroxide concentration, pOH, and pH for strontium hydroxide solutions. By default, it evaluates the classic problem: 2.0 × 10-3 M Sr(OH)2.
pH Calculator
For 2.0 × 10^-3, enter 2.0 here.
For 2.0 × 10^-3, enter -3.
Strong base assumption is used for these compounds.
This calculator uses the standard 25°C relationship.
Results
Ready to calculate
Enter the concentration in scientific notation and click Calculate pH. For the default problem, the expected pH is slightly above 11.6 because Sr(OH)2 releases two hydroxide ions per formula unit.
How to calculate pH for 2.0 × 10-3 M Sr(OH)2
When students search for “calculate pH for 2.0 10 3 m sr oh 2,” they are almost always referring to the chemistry problem written more formally as calculate the pH of a 2.0 × 10-3 M Sr(OH)2 solution. This is a classic general chemistry exercise because it blends several core skills: reading scientific notation correctly, recognizing strong bases, accounting for stoichiometry, converting hydroxide concentration to pOH, and then converting pOH to pH.
The key idea is that strontium hydroxide, Sr(OH)2, is treated as a strong base in introductory chemistry. Strong bases dissociate essentially completely in water. That means one formula unit of Sr(OH)2 breaks apart to produce one Sr2+ ion and two OH– ions. Because two hydroxides are released per mole of dissolved Sr(OH)2, the hydroxide concentration is double the molar concentration of the base.
Step 1: Write the dissociation equation
The first thing to do is write the balanced dissociation of strontium hydroxide in water:
Sr(OH)2(aq) → Sr2+(aq) + 2OH–(aq)
This equation tells you the stoichiometric relationship. Every 1 mole of Sr(OH)2 yields 2 moles of hydroxide ions. If the solution concentration is 2.0 × 10-3 M in Sr(OH)2, then:
[OH–] = 2 × (2.0 × 10-3) = 4.0 × 10-3 M
Step 2: Calculate pOH
Once you know the hydroxide concentration, apply the pOH formula:
pOH = -log[OH–]
Substitute 4.0 × 10-3 M:
pOH = -log(4.0 × 10-3)
Evaluating this gives:
pOH ≈ 2.40
More precisely, with the usual significant figure treatment, pOH is about 2.398.
Step 3: Convert pOH to pH
At 25°C, the standard relationship is:
pH + pOH = 14.00
So:
pH = 14.00 – 2.40 = 11.60
Therefore, the pH of 2.0 × 10-3 M Sr(OH)2 is approximately:
pH = 11.60
Why Sr(OH)2 gives a basic pH above 11
Strontium hydroxide belongs to the family of metal hydroxides that strongly increase hydroxide concentration in water. Since pH is a logarithmic scale, a hydroxide concentration of 4.0 × 10-3 M is substantial enough to push the solution well into the basic range. Neutral water at 25°C has pH 7.00. A pH of 11.60 means the solution is thousands of times more basic than neutral water when judged by hydrogen ion concentration.
This is also a good place to remember that pH values are not linear. A shift from pH 10.60 to pH 11.60 is a tenfold change in hydrogen ion concentration. Because of this logarithmic behavior, even small numerical changes in pH can represent major chemical differences.
Full worked example for the exact problem
- Given concentration of base: 2.0 × 10-3 M Sr(OH)2
- Dissociation: Sr(OH)2 → Sr2+ + 2OH–
- Hydroxide concentration: [OH–] = 2 × 2.0 × 10-3 = 4.0 × 10-3 M
- pOH calculation: pOH = -log(4.0 × 10-3) ≈ 2.40
- pH calculation: pH = 14.00 – 2.40 = 11.60
If your instructor expects the answer with two decimal places, 11.60 is ideal. If they want proper significant figure reasoning based on the 2.0 concentration, that still usually leads to reporting two digits after the decimal place in the pH.
Common mistakes students make
- Forgetting the coefficient of 2 for OH–: This is the biggest error. Sr(OH)2 does not produce one hydroxide ion. It produces two.
- Using pH = -log[OH–]: That equation gives pOH, not pH.
- Dropping the negative exponent incorrectly: 10-3 means one-thousandth, not one thousand.
- Ignoring the 25°C assumption: In standard textbook problems, pH + pOH = 14.00 is used at 25°C.
- Rounding too early: Keep extra digits until the final step.
Quick comparison with other strong bases
Stoichiometry matters a lot when comparing bases. A 2.0 × 10-3 M solution of NaOH produces 2.0 × 10-3 M OH–, but the same concentration of Sr(OH)2 produces 4.0 × 10-3 M OH–. That means the strontium hydroxide solution is more basic at the same formal molarity.
| Base | Dissociation Pattern | OH– Produced per Mole of Base | [OH–] at 2.0 × 10-3 M Base | Approximate pH at 25°C |
|---|---|---|---|---|
| NaOH | NaOH → Na+ + OH– | 1 | 2.0 × 10-3 M | 11.30 |
| KOH | KOH → K+ + OH– | 1 | 2.0 × 10-3 M | 11.30 |
| Ca(OH)2 | Ca(OH)2 → Ca2+ + 2OH– | 2 | 4.0 × 10-3 M | 11.60 |
| Sr(OH)2 | Sr(OH)2 → Sr2+ + 2OH– | 2 | 4.0 × 10-3 M | 11.60 |
| Ba(OH)2 | Ba(OH)2 → Ba2+ + 2OH– | 2 | 4.0 × 10-3 M | 11.60 |
Scientific context and useful real data
Hydrogen ion concentration in pure water at 25°C is approximately 1.0 × 10-7 M, which defines the familiar neutral point of pH 7. The ion-product constant for water, Kw, is approximately 1.0 × 10-14 at 25°C. These benchmark values are what make the equation pH + pOH = 14.00 so useful in introductory chemistry. In a strong-base solution like this one, [OH–] is dominated by the dissolved base, not by the tiny autoionization of water.
In environmental and industrial settings, highly basic solutions can affect corrosion, scaling, treatment chemistry, and safety procedures. Although this calculator is aimed at classroom chemistry, the underlying pH concept matters in water treatment, laboratory reagent preparation, and chemical manufacturing.
| Reference Quantity | Typical Value at 25°C | Why It Matters for This Problem |
|---|---|---|
| Neutral pH of pure water | 7.00 | Provides the baseline for comparing how basic 11.60 really is. |
| Ion-product constant of water, Kw | 1.0 × 10-14 | Supports the relationship pH + pOH = 14.00 at 25°C. |
| Hydrogen ion concentration in neutral water | 1.0 × 10-7 M | Shows how far a pH 11.60 solution is from neutrality. |
| Hydroxide concentration for this Sr(OH)2 problem | 4.0 × 10-3 M | Directly used to compute pOH and then pH. |
When the simple method works best
The method used here works best under the assumptions of introductory chemistry:
- The base is strong and dissociates completely.
- The solution is dilute enough that activity corrections are not required.
- The temperature is approximately 25°C.
- You are asked for a classroom-style pH estimate rather than a rigorous thermodynamic treatment.
For advanced analytical chemistry, high ionic strength solutions may require activities instead of concentrations. However, for a problem like 2.0 × 10-3 M Sr(OH)2, the textbook approach is absolutely appropriate and is the expected solution in most general chemistry courses.
How to remember the formula without confusion
A fast mental framework can save a lot of mistakes:
- Identify whether the compound is an acid or base. Sr(OH)2 is a base because it contains hydroxide.
- Count the number of OH groups. There are 2 hydroxides, so multiply concentration by 2.
- Find pOH first. Bases naturally give [OH–], so compute pOH = -log[OH–].
- Use 14.00 – pOH. That gives pH at 25°C.
This mental checklist works for many strong bases. It is especially helpful when comparing compounds like NaOH, Ca(OH)2, and Sr(OH)2 where the number of hydroxide ions released per formula unit changes the answer.
Authoritative chemistry references
For students who want to verify the theory from high-quality scientific and educational sources, these references are excellent starting points:
- U.S. Environmental Protection Agency: Water Quality Criteria and pH context
- Chemistry LibreTexts hosted by educational institutions
- U.S. Geological Survey: pH and Water
Final answer
If the question is calculate the pH for 2.0 × 10-3 M Sr(OH)2, then the correct textbook result is:
[OH–] = 4.0 × 10-3 M
pOH = 2.40
pH = 11.60