Determine The Ph In A 0.667 M Naoh Solution

Determining the pH of a 0.667 M NaOH Solution: A Comprehensive Guide

Determining the pH of a solution is a fundamental concept in chemistry with wide-ranging applications, from environmental monitoring to industrial processes. This article will delve into the detailed calculation of the pH of a 0.667 M sodium hydroxide (NaOH) solution, explaining the underlying principles and providing a step-by-step approach. We'll also explore the implications of this calculation and discuss potential sources of error.

Understanding pH and pOH

Before we begin the calculation, let's refresh our understanding of pH and pOH. pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm (base 10) of the hydrogen ion concentration ([H⁺]):

pH = -log₁₀[H⁺]

A lower pH value indicates a more acidic solution, while a higher pH value indicates a more basic (alkaline) solution. A pH of 7 is considered neutral at 25°C.

pOH, on the other hand, is a measure of the hydroxide ion concentration ([OH⁻]):

pOH = -log₁₀[OH⁻]

The relationship between pH and pOH at 25°C is given by:

pH + pOH = 14

NaOH: A Strong Base

Sodium hydroxide (NaOH), also known as lye or caustic soda, is a strong base. This means it completely dissociates in water, releasing its hydroxide ions (OH⁻) into the solution. The dissociation reaction is:

NaOH(aq) → Na⁺(aq) + OH⁻(aq)

This complete dissociation is crucial for calculating the pH of the solution because it allows us to directly relate the concentration of NaOH to the concentration of OH⁻ ions.

Calculating the pOH of a 0.667 M NaOH Solution

Since NaOH is a strong base and completely dissociates, the concentration of OH⁻ ions is equal to the concentration of NaOH. Therefore, in a 0.667 M NaOH solution:

[OH⁻] = 0.667 M

Now we can calculate the pOH:

pOH = -log₁₀(0.667) pOH ≈ 0.176

Calculating the pH of a 0.667 M NaOH Solution

Using the relationship between pH and pOH at 25°C (pH + pOH = 14), we can now calculate the pH:

pH = 14 - pOH pH = 14 - 0.176 pH ≈ 13.824

Therefore, the pH of a 0.667 M NaOH solution is approximately 13.82.

Significance of the Result and Practical Applications

The high pH value of 13.82 indicates that the 0.667 M NaOH solution is highly alkaline. This has significant implications in various applications:

Industrial Applications:

• Chemical Manufacturing: NaOH is a crucial reagent in numerous chemical processes, including the production of soaps, detergents, and paper. Understanding its pH is critical for controlling reaction rates and product quality.
• Water Treatment: NaOH is used to adjust the pH of water in various treatment processes. Precise pH control is essential for effective water purification and disinfection.
• Wastewater Treatment: NaOH is employed to neutralize acidic waste streams, preventing environmental damage. Accurate pH measurements are vital for ensuring efficient and safe wastewater treatment.

Laboratory Applications:

• Titrations: NaOH is a common titrant in acid-base titrations, where its precise concentration and pH are critical for accurate determination of unknown acid concentrations.
• pH Buffers: While NaOH itself isn't a buffer, understanding its pH helps in preparing and utilizing buffer solutions that maintain a specific pH range.
• Chemical Synthesis: In organic chemistry, NaOH is used in various reactions, often requiring precise pH control for optimal yields and selectivity.

Everyday Applications:

• Drain Cleaners: Many drain cleaners contain NaOH to dissolve organic matter clogging drains. The high pH contributes to its effectiveness but also presents safety concerns.
• Food Processing: Although less common, NaOH may be used in some food processing applications, requiring careful control to meet safety and quality standards.

Potential Sources of Error and Considerations

While the calculation presented above is straightforward, several factors can influence the actual pH of a 0.667 M NaOH solution:

Temperature Effects:

The relationship between pH and pOH (pH + pOH = 14) is only valid at 25°C. At other temperatures, the ionic product of water (Kw) changes, affecting the pH calculation. Higher temperatures lead to a slightly lower pH for a given concentration of NaOH.

Activity Coefficients:

The calculation assumes that the activity of the hydroxide ions is equal to their concentration. This is not strictly accurate at high concentrations due to interionic interactions. Activity coefficients correct for these deviations but require more complex calculations.

Purity of NaOH:

The purity of the NaOH sample used can significantly affect the concentration and hence the pH of the solution. Impurities can introduce other ions that may influence the pH.

Measurement Errors:

Errors can occur during the measurement of the NaOH concentration and the pH using instruments like pH meters. Calibration and proper technique are essential to minimize these errors.

Ionization of Water:

At very high concentrations, the autoprotolysis of water contributes to the overall hydroxide ion concentration, subtly affecting the calculated pH. While negligible in this case, it's a consideration for extremely concentrated solutions.

Conclusion

Determining the pH of a 0.667 M NaOH solution involves a relatively straightforward calculation based on its complete dissociation as a strong base. The resulting pH of approximately 13.82 highlights the highly alkaline nature of this solution, underscoring its significant role in various industrial, laboratory, and even everyday applications. However, it is crucial to acknowledge the potential sources of error that can affect the accuracy of the calculation, including temperature variations, activity coefficients, and the purity of the NaOH sample. Accurate pH measurement and careful consideration of these factors are essential for obtaining reliable results in any application involving NaOH solutions. Further exploration into activity coefficients and their impact on high-concentration solutions would provide a more comprehensive understanding of the true pH.