4 Calculate The Ph of A 0.0010 M Naoh Solution
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Calculating the pH of a sodium hydroxide (NaOH) solution is essential in chemistry, environmental science, and industrial applications. This guide explains how to determine the pH of a 0.0010 M NaOH solution using the proper formula and interpretation techniques.
Introduction
The pH scale measures how acidic or basic a solution is, ranging from 0 (very acidic) to 14 (very basic). For sodium hydroxide (NaOH), which is a strong base, the pH calculation follows specific chemical principles.
When NaOH dissolves in water, it dissociates completely into sodium (Na⁺) and hydroxide (OH⁻) ions. The concentration of hydroxide ions determines the pH of the solution.
pH Calculation Formula
The pH of a solution can be calculated using the concentration of hydroxide ions (OH⁻) with the following formula:
pH = 14 + log[OH⁻]
Where [OH⁻] is the molar concentration of hydroxide ions.
For a 0.0010 M NaOH solution:
- The concentration of OH⁻ ions is equal to the concentration of NaOH because NaOH completely dissociates in water.
- Therefore, [OH⁻] = 0.0010 M.
Worked Example
Let's calculate the pH of a 0.0010 M NaOH solution step by step.
- Identify the concentration of OH⁻ ions: [OH⁻] = 0.0010 M.
- Use the pH formula: pH = 14 + log[OH⁻].
- Calculate the logarithm: log(0.0010) = -3.
- Add to 14: pH = 14 + (-3) = 11.
The pH of a 0.0010 M NaOH solution is 11.
Note: This calculation assumes the solution is dilute and the activity coefficient is 1. For more concentrated solutions, activity corrections may be needed.
Interpreting Results
A pH of 11 indicates a strongly basic solution. This means:
- The solution contains a high concentration of hydroxide ions.
- It will react strongly with acids.
- It may be corrosive to metals and some plastics.
Comparison table of pH values:
| pH Range | Classification | Example Solutions |
|---|---|---|
| 0-6 | Acidic | Lemon juice, vinegar, stomach acid |
| 7 | Neutral | Pure water, distilled water |
| 8-14 | Basic | NaOH, bleach, soap |
FAQ
Why does NaOH have a pH of 11 in a 0.0010 M solution?
NaOH is a strong base that completely dissociates in water, so the concentration of OH⁻ ions equals the concentration of NaOH. The pH formula then gives a value of 11 for this concentration.
Can I use this formula for any NaOH concentration?
This formula works well for dilute solutions. For more concentrated solutions (above 0.1 M), you may need to account for activity effects using the Debye-Hückel equation.
What happens if I dilute the NaOH solution?
Diluting the solution will decrease the concentration of OH⁻ ions, resulting in a higher pH value. The pH will increase logarithmically with dilution.