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pH Calculation for Weak Acid:
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The pH calculation for weak acids estimates the acidity of a solution based on the acid dissociation constant (Ka) and the concentration of the acid. This approximation assumes [H⁺] = √(Ka × C) and is valid for weak acids where dissociation is limited.
The calculator uses the formula:
Where:
Explanation: The formula calculates the hydrogen ion concentration from the square root of the product of Ka and concentration, then converts it to pH using the negative logarithm.
Details: Accurate pH calculation is crucial for understanding acid-base chemistry, predicting chemical behavior in solutions, and applications in biochemistry, environmental science, and industrial processes.
Tips: Enter Ka value in mol/L and concentration in mol/L. Both values must be positive numbers. The calculator is specifically designed for weak acids where this approximation is valid.
Q1: When is this approximation valid?
A: This approximation works best for weak acids where Ka is small (typically < 10⁻³) and the concentration is not extremely dilute.
Q2: What are the limitations of this calculation?
A: It doesn't account for water's autoionization (important for very dilute solutions) or activity coefficients. For strong acids or very concentrated solutions, different calculations are needed.
Q3: How accurate is this pH estimation?
A: For typical weak acid solutions, it provides a good estimate, usually within 0.1-0.2 pH units of more precise calculations.
Q4: Can I use this for polyprotic acids?
A: This calculator is designed for monoprotic weak acids. For polyprotic acids, additional considerations are needed for accurate pH calculation.
Q5: What if my acid concentration is very low?
A: For concentrations below about 10⁻⁶ M, the contribution from water's autoionization becomes significant and this approximation may not be accurate.