Calculate Ph For 1.0 10 3 M Sr Oh 2

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Calculate pH for 1.0 × 10-3 M Sr(OH)2

Use this premium calculator to determine hydroxide concentration, pOH, and pH for aqueous strontium hydroxide. The default setup solves the classic chemistry problem for 1.0 × 10-3 M Sr(OH)2, while also letting you test other concentrations and temperatures.

Enter values and click Calculate pH to see the full solution for Sr(OH)2.

Visual Breakdown of the Solution

The chart compares the dissolved base concentration, generated hydroxide concentration, pOH, and final pH for your selected setup.

How to Calculate pH for 1.0 × 10-3 M Sr(OH)2

If you need to calculate pH for 1.0 × 10-3 M Sr(OH)2, the key idea is that strontium hydroxide is treated as a strong base in introductory and most intermediate chemistry settings. That means it dissociates essentially completely in water:

Sr(OH)2(aq) → Sr2+(aq) + 2 OH-(aq)

Because each mole of Sr(OH)2 releases two moles of hydroxide ions, the hydroxide concentration is double the formal molarity of the dissolved base. For a solution that is 1.0 × 10-3 M in Sr(OH)2, the hydroxide concentration becomes:

  1. Start with the given base concentration: [Sr(OH)2] = 1.0 × 10^-3 M
  2. Use stoichiometry from dissociation: [OH-] = 2 × [Sr(OH)2]
  3. Substitute values: [OH-] = 2 × 1.0 × 10^-3 = 2.0 × 10^-3 M
  4. Calculate pOH: pOH = -log(2.0 × 10^-3)
  5. At 25 degrees C, calculate pH: pH = 14.00 – pOH

Performing the logarithm gives a pOH of about 2.699, so the final pH is approximately 11.301. Rounded reasonably for most coursework, the answer is usually reported as pH = 11.30.

Final standard answer at 25 degrees C: pH ≈ 11.30 for 1.0 × 10-3 M Sr(OH)2, assuming complete dissociation.

Why Sr(OH)2 Produces Two Hydroxide Ions

This problem is often missed because students remember that a strong base increases pH, but they forget to account for stoichiometry. Strontium hydroxide has the formula Sr(OH)2. The subscript 2 on hydroxide means that each formula unit contributes two OH– ions when it dissociates in water. That is why you do not use 1.0 × 10^-3 M directly as the hydroxide concentration. Instead, you must double it.

Compare that with sodium hydroxide, NaOH, which contributes only one hydroxide ion per formula unit. A 1.0 × 10-3 M NaOH solution would have [OH-] = 1.0 × 10^-3 M, but a 1.0 × 10-3 M Sr(OH)2 solution has [OH-] = 2.0 × 10^-3 M.

Step-by-Step Chemistry Logic

Here is the full reasoning in a format you can use for homework, lab reports, quizzes, or exam review:

  • Identify the solute type: Sr(OH)2 is a strong base.
  • Write the dissociation equation: Sr(OH)2 → Sr2+ + 2OH–
  • Determine hydroxide concentration: multiply the base molarity by 2.
  • Find pOH: use pOH = -log[OH-].
  • Convert to pH: at 25 degrees C, pH + pOH = 14.00.

In numeric form:

[OH-] = 2(1.0 × 10^-3) = 2.0 × 10^-3 M
pOH = -log(2.0 × 10^-3) = 2.699
pH = 14.00 – 2.699 = 11.301

Common Student Mistakes When Solving This Problem

Even though this is a short strong-base problem, there are several classic mistakes:

  1. Forgetting the coefficient of 2 for OH–. This is the most common error.
  2. Using pH = -log[OH–]. That expression gives pOH, not pH.
  3. Ignoring temperature assumptions. The relationship pH + pOH = 14.00 is exact only at 25 degrees C.
  4. Using the wrong scientific notation. 10-3 means 0.001, not 0.0001.
  5. Rounding too early. Keep extra digits through the logarithm step, then round at the end.

Comparison Table: Strong Bases at the Same Formal Concentration

The table below shows how hydroxide yield changes with base formula. This helps explain why Sr(OH)2 gives a higher pH than a monohydroxide base at the same molarity.

Base Formal Concentration (M) OH– Released per Formula Unit [OH–] (M) pOH at 25 degrees C pH at 25 degrees C
NaOH 1.0 × 10-3 1 1.0 × 10-3 3.000 11.000
KOH 1.0 × 10-3 1 1.0 × 10-3 3.000 11.000
Ca(OH)2 1.0 × 10-3 2 2.0 × 10-3 2.699 11.301
Sr(OH)2 1.0 × 10-3 2 2.0 × 10-3 2.699 11.301
Ba(OH)2 1.0 × 10-3 2 2.0 × 10-3 2.699 11.301

Real Statistics: pH Scale Benchmarks

To put the result in context, a pH of about 11.30 is clearly basic. The pH scale is logarithmic, so each one-unit change reflects a tenfold change in hydrogen ion activity. Neutral pure water at 25 degrees C has pH 7.00, while this Sr(OH)2 solution is several orders of magnitude more basic than neutral water.

Reference System Typical pH Interpretation
Pure water at 25 degrees C 7.00 Neutral benchmark used in general chemistry
Natural rain (unpolluted average) About 5.6 Slightly acidic due to dissolved carbon dioxide
Seawater About 8.1 Mildly basic natural system
1.0 × 10-3 M NaOH 11.00 Basic strong monohydroxide solution
1.0 × 10-3 M Sr(OH)2 11.30 More basic because 2 OH– ions are produced
Household bleach 11 to 13 Strongly basic consumer product range

Does Water Autoionization Matter Here?

In very dilute acid-base problems, the self-ionization of water can matter. However, for a hydroxide concentration of 2.0 × 10^-3 M, the contribution from pure water is tiny by comparison. At 25 degrees C, pure water contributes only about 1.0 × 10^-7 M each of H+ and OH–. Since 2.0 × 10^-3 M is much larger than 1.0 × 10^-7 M, ignoring water autoionization is fully justified for this calculation.

What If the Temperature Is Not 25 Degrees C?

This calculator includes alternate temperature assumptions because the ionic product of water, Kw, changes with temperature. That means the familiar shortcut pH + pOH = 14.00 applies specifically to 25 degrees C. At other temperatures, the sum is different. In many classroom settings, unless your instructor states otherwise, you should assume the problem is at 25 degrees C.

For this reason, if your textbook question simply asks you to calculate pH for 1.0 × 10-3 M Sr(OH)2, the expected answer is almost always 11.30.

Worked Example in Compact Exam Format

If you want a concise write-up for an exam, use this:

  1. Sr(OH)2 → Sr2+ + 2OH-
  2. [OH-] = 2(1.0 × 10^-3) = 2.0 × 10^-3 M
  3. pOH = -log(2.0 × 10^-3) = 2.699
  4. pH = 14.00 – 2.699 = 11.301
  5. Answer: pH = 11.30

Why This Problem Is a Good Acid-Base Skills Check

Chemistry instructors like this problem because it checks several concepts at once. You must recognize a strong base, write the dissociation correctly, use stoichiometric coefficients, perform a logarithm, and convert pOH to pH. It is simple enough to solve quickly but still exposes whether the student understands the structure of ionic hydroxides.

It also reinforces an important broader rule: the chemical formula matters. Compounds with two hydroxide groups are not interchangeable with compounds that have only one. Looking carefully at subscripts is often the difference between a correct and incorrect final answer.

Authoritative References for pH, Water Chemistry, and Acid-Base Fundamentals

Bottom Line

To calculate pH for 1.0 × 10-3 M Sr(OH)2, first double the concentration to get hydroxide because each dissolved unit releases two OH– ions. That gives [OH-] = 2.0 × 10^-3 M. Then calculate pOH = 2.699 and finally pH = 11.301. Under the standard 25 degrees C assumption, the reported answer is:

pH = 11.30

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