Calculating the Concentration of Calcium Hydroxide from pH

This tutorial aims to help you calculate the concentration of calcium hydroxide (Ca(OH)2) in a solution using its pH. Understanding this process is crucial for various applications, from environmental science to industrial chemistry.

Introduction to pH and pOH

The acidity or basicity of a solution is described by its pH. In aqueous solutions, pH is defined as the negative logarithm of the hydrogen ion concentration:

pH -log[H ]

Another useful parameter is pOH, which is the negative logarithm of the hydroxide ion concentration:

pOH -log[OH-]

The relationship between pH and pOH is given by:

pH pOH 14.00

Given Data and Calculations

Consider a solution of calcium hydroxide with a pH of 10.33. We need to find the concentration of calcium hydroxide in the solution.

Step 1: Calculate pOH

Since pH pOH 14.00, we can calculate pOH as follows:

pOH 14.00 - pH 14.00 - 10.33 3.67

Step 2: Calculate Hydroxide Ion Concentration [OH-]

Using the definition of pOH:

[OH-] 10^{-pOH} 10^{-3.67} approx 2.14 times 10^{-4}

Step 3: Relate [OH-] to Calcium Hydroxide [Ca(OH)2]

Calcium hydroxide dissociates in water as:

Ca(OH)2 Ca2 2OH-

For every mole of Ca(OH)2 that dissolves, it produces 2 moles of OH-. Therefore:

[Ca(OH)2] frac{[OH-]}{2} frac{2.14 times 10^{-4}}{2} approx 1.07 times 10^{-4}

Final Result

The concentration of calcium hydroxide in the solution is approximately:

[Ca(OH)2] 1.07 times 10^{-4} M

Calculating pH and pOH on Different Calculators

It's important to know how to calculate pH and pOH on your specific calculator. Here’s a step-by-step guide for a few different types:

Example 1: Calculating PH

If the given pH is 10.33:

[H ] 10^{-10.33}

Calculator Type 1: 10^x 10.33 [-] Calculator Type 2: INV [log] [-] 10.33 Combination Calculator: 10 [-] 10.33

Remember: Use your calculator’s instructions for accurate calculations.

Example 2: Calculating [OH-]

If you want to find [OH-] from [H ], where [H ] 10^(-pH), use:

[OH-] frac{10^{-14}}{[H ]} frac{1 times 10^{-14}}{10^x}

Calculator Type 1: 1 EXP [-] 14 / [10^x] Calculator Type 2: 1 EE [-] 14 / [10^x] Combination Calculator: 1 10 [-] 1 [-] 14 / [10^x]

Refer to your calculator’s manual for exact key combinations.

Conclusion

Understanding and calculating the concentration of calcium hydroxide from pH is a fundamental skill in chemistry. Whether you’re working in a laboratory or dealing with environmental concerns, mastering these calculations can be invaluable.