Calculate the pOH of a 0.2 M HCl Solution

pOH Calculation Formula:

\[ \text{pOH} = 14 - \text{pH} \] \[ \text{pH} = -\log[\text{H}^+] \]

pH:

pOH:

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1. What is pOH?

pOH is a measure of the hydroxide ion (OH⁻) concentration in a solution. It's related to pH through the equation: pOH = 14 - pH. For strong acids like HCl, which completely dissociate in water, the hydrogen ion concentration equals the acid concentration.

2. How Does the Calculator Work?

The calculator uses the following formulas:

\[ \text{pH} = -\log[\text{H}^+] \] \[ \text{pOH} = 14 - \text{pH} \]

Where:

\( [\text{H}^+] \) — Hydrogen ion concentration (equal to HCl concentration for strong acids)
pH — Measure of acidity
pOH — Measure of hydroxide ion concentration

Explanation: For strong acids like HCl, the pH is calculated directly from the acid concentration, and pOH is derived from the pH.

3. Importance of pOH Calculation

Details: pOH is important in acid-base chemistry, particularly when working with basic solutions or when you need to know hydroxide ion concentration. It's especially useful in buffer solutions and titration calculations.

4. Using the Calculator

Tips: Enter the HCl concentration in molarity (M). The calculator will compute both pH and pOH values. The default value is 0.2 M.

5. Frequently Asked Questions (FAQ)

Q1: Why is pOH important if we usually talk about pH?
A: While pH is more commonly used, pOH is directly related to hydroxide ion concentration and is particularly useful in basic solutions or when calculating equilibrium constants.

Q2: What's the relationship between pH and pOH?
A: In aqueous solutions at 25°C, pH + pOH = 14. This relationship comes from the ion product of water (Kw = [H+][OH-] = 1×10⁻¹⁴).

Q3: Does this calculation work for weak acids?
A: No, this calculator is for strong acids only. Weak acids don't completely dissociate, so their pH calculation requires knowledge of the acid dissociation constant (Ka).

Q4: What are typical pOH values for acidic solutions?
A: For acidic solutions (pH < 7), pOH will be >7. A 0.2 M HCl solution has pH ≈ 0.70 and pOH ≈ 13.30.

Q5: How does temperature affect pOH?
A: The pH + pOH relationship changes with temperature because Kw is temperature-dependent. At higher temperatures, the neutral point (pH = pOH) shifts from 7.