7.54 × 10-4 M Sr(OH)2 Calculate pH
Use this premium calculator to find hydroxide concentration, pOH, and pH for strontium hydroxide solutions. The default example is 7.54 × 10-4 M Sr(OH)2 at 25°C, assuming complete dissociation.
Calculation Results
Enter or keep the default values, then click Calculate pH.
How to calculate the pH of 7.54 × 10-4 M Sr(OH)2
If your chemistry problem asks you to solve “7.54 10 4 m sr oh 2 calculate ph”, it is almost always shorthand for 7.54 × 10-4 M Sr(OH)2, where Sr(OH)2 is strontium hydroxide. This is a strong base, which means it dissociates essentially completely in water under typical introductory chemistry assumptions. Because each formula unit of strontium hydroxide produces two hydroxide ions, the pH calculation is not based directly on the stated molarity of the base alone. Instead, you first convert the concentration of Sr(OH)2 into hydroxide ion concentration, then find pOH, and finally convert that into pH.
The default example in this calculator uses a solution concentration of 7.54 × 10-4 M. Since Sr(OH)2 dissociates according to the equation Sr(OH)2 → Sr2+ + 2OH–, the hydroxide concentration is double the strontium hydroxide concentration. That single stoichiometric detail is the most important reason students sometimes get this problem wrong. They compute pOH from 7.54 × 10-4 directly, which would ignore the extra OH– produced by every dissolved unit of the base.
Step-by-step solution for 7.54 × 10-4 M Sr(OH)2
- Write the dissociation relationship: Sr(OH)2 gives 2 OH– for every 1 mole of Sr(OH)2.
- Calculate hydroxide concentration: [OH–] = 2 × 7.54 × 10-4 = 1.508 × 10-3 M.
- Find pOH using pOH = -log[OH–].
- Compute pOH: pOH = -log(1.508 × 10-3) ≈ 2.82.
- Use pH + pOH = 14.00 at 25°C.
- Find pH: pH = 14.00 – 2.82 = 11.18.
Therefore, the pH of 7.54 × 10-4 M Sr(OH)2 is approximately 11.18. Depending on your instructor’s rounding rules, you may report this as 11.18 or 11.179. Because the concentration is given with three significant figures, reporting to two decimal places is common and reasonable for pH in many classroom settings.
Why Sr(OH)2 changes the math compared with NaOH
Many students are comfortable calculating pH for a monohydroxide base such as NaOH or KOH. In those cases, one mole of dissolved base gives one mole of hydroxide ions, so the hydroxide concentration equals the base concentration. Strontium hydroxide is different because it is a di-hydroxide. Every mole releases two moles of OH–. That means the hydroxide concentration is doubled before the logarithm step.
This matters because the pH scale is logarithmic rather than linear. Doubling [OH–] does not add a full 1.00 pH unit, but it definitely changes the final answer. In fact, doubling the hydroxide concentration changes pOH by about 0.30 units because log(2) ≈ 0.3010. So if you forget the coefficient of 2, your pH will be off by about 0.30, which is a large error in a chemistry calculation.
| Compound | Dissociation pattern | OH– ions released per formula unit | Result if base concentration is 7.54 × 10-4 M |
|---|---|---|---|
| NaOH | NaOH → Na+ + OH– | 1 | [OH–] = 7.54 × 10-4 M |
| KOH | KOH → K+ + OH– | 1 | [OH–] = 7.54 × 10-4 M |
| Sr(OH)2 | Sr(OH)2 → Sr2+ + 2OH– | 2 | [OH–] = 1.508 × 10-3 M |
| Ba(OH)2 | Ba(OH)2 → Ba2+ + 2OH– | 2 | [OH–] = 1.508 × 10-3 M |
Detailed explanation of the chemistry behind the answer
pH measures the acidity or basicity of an aqueous solution. More specifically, pH is defined from hydrogen ion activity and is commonly approximated in general chemistry as the negative logarithm of hydrogen ion concentration. For basic solutions, it is often easier to work through pOH first. Hydroxide concentration tells us how basic the solution is, and then we use the relationship pH + pOH = 14.00 at 25°C.
Strong bases such as Sr(OH)2 are typically assumed to dissociate completely in water. That means if you place 7.54 × 10-4 moles of Sr(OH)2 in enough water to make one liter of solution, essentially all of those dissolved units split into ions. The strontium ion itself does not determine the pH in the simplified treatment. The dominant contribution comes from hydroxide ions produced in solution.
Once you know [OH–] = 1.508 × 10-3 M, the rest is logarithmic conversion. This is where scientific notation is especially useful. A concentration written as 1.508 × 10-3 naturally indicates a pOH a little below 3. If the concentration had been exactly 1.00 × 10-3, the pOH would be exactly 3.00. Because 1.508 is greater than 1, the pOH becomes a little smaller than 3, giving a pOH near 2.82. Then the pH becomes a little above 11.
Common mistakes students make
- Forgetting the coefficient of 2. Sr(OH)2 produces two hydroxides, not one.
- Using pH = -log[OH–]. That formula gives pOH, not pH.
- Dropping the negative exponent incorrectly. 10-4 means the decimal moves four places left.
- Rounding too early. Keep extra digits through the pOH step, then round the final pH.
- Ignoring temperature assumptions. In standard chemistry exercises, pH + pOH = 14.00 is usually assumed at 25°C.
Real statistics and comparison data related to pH
The pH scale is not just a classroom idea. It is used constantly in environmental chemistry, water treatment, manufacturing, agriculture, and laboratory work. For context, natural waters and regulated drinking waters occupy a much narrower pH range than the strong basic solution in this problem. A pH of 11.18 is far above ordinary drinking water conditions and firmly in the basic range.
| Water or solution type | Typical or recommended pH range | Comparison to pH 11.18 | Source context |
|---|---|---|---|
| Pure water at 25°C | About 7.00 | pH 11.18 is 4.18 pH units higher | Standard chemistry reference point |
| EPA secondary drinking water guideline range | 6.5 to 8.5 | pH 11.18 is well above the upper aesthetic guideline | U.S. EPA guidance |
| Typical rainwater | About 5.0 to 5.6 | pH 11.18 is strongly basic compared with weakly acidic rain | Environmental chemistry benchmark |
| Seawater | About 8.0 to 8.3 | pH 11.18 is substantially more basic | Marine chemistry benchmark |
These comparisons show why the answer to this problem should “feel” basic even before you complete the calculation. A hydroxide concentration on the order of 10-3 M corresponds to a pOH near 3, which places the pH near 11. That is significantly more alkaline than common environmental waters.
Why pH 11.18 is much more basic than pH 8.18
Because pH is logarithmic, a difference of 3 pH units is enormous. A solution at pH 11.18 is about 103, or roughly 1,000 times, lower in hydrogen ion concentration than a solution at pH 8.18. This is a useful way to build intuition. Even though the numeric gap looks small, the chemical difference is large.
When the simple strong-base method works best
The direct method used by this calculator is appropriate for standard general chemistry and homework problems where the base is treated as strong and fully dissociated. It is especially useful when the concentration is not extremely tiny and when the problem statement clearly expects the 25°C relation pH + pOH = 14.00. For highly dilute solutions, very precise work, or advanced physical chemistry settings, water autoionization and activity effects may matter more. But for a problem stated as 7.54 × 10-4 M Sr(OH)2, the standard classroom method is exactly what most instructors want.
Short memory trick for multi-hydroxide bases
- Read the formula carefully.
- Count the number of OH groups.
- Multiply base molarity by that count.
- Use the resulting hydroxide concentration for pOH.
- Convert pOH to pH at 25°C.
Authoritative references for pH and water chemistry
If you want deeper background on pH, water quality, and standard measurement concepts, these resources are useful:
- U.S. Environmental Protection Agency: pH overview
- National Institute of Standards and Technology: Physical Measurement Laboratory
- U.S. Geological Survey: pH and Water
Final answer for 7.54 × 10-4 M Sr(OH)2
To summarize the entire process: start with the base concentration, recognize that strontium hydroxide releases two hydroxide ions, double the concentration to get [OH–], calculate pOH with the negative logarithm, and subtract from 14. Using that approach, the hydroxide concentration is 1.508 × 10-3 M, the pOH is 2.82, and the pH is 11.18.
So if your assignment or search prompt is “7.54 10 4 m sr oh 2 calculate ph,” the correct final result is: pH ≈ 11.18.