PERHITUNGAN pH ASAM LEMAH DAN BASA LEMAH

Summary

This educational video tutorial explains how to calculate the pH of weak acids and bases, breaking down the concepts into clear steps with practical examples. It covers the basic formulas for determining hydrogen and hydroxide ion concentrations from given dissociation constants and concentrations. The tutorial also walks through how to calculate pH and pOH, and includes detailed problem-solving examples, such as finding the pH of an HF solution and determining the mass of acetic acid needed to prepare a specific solution. This comprehensive guide helps learners understand the core principles of pH calculations for weak acids and bases.

Takeaways

• 😀 Weak acids and weak bases do not fully dissociate in water, requiring specific methods to calculate their pH.
• 😀 The pH of a weak acid can be determined using the formula: [H⁺] = √(Ka × [Acid]).
• 😀 Weak acids like HF, acetic acid, and H₂SO₃ require knowledge of their dissociation constant (Ka) for pH calculations.
• 😀 For weak bases, the pH can be found using the formula: [OH⁻] = √(Kb × [Base]).
• 😀 The pH of a weak base can be related to its pOH and then converted to pH by subtracting from 14.
• 😀 Example 1: For a 0.001 M HF solution with Ka = 4 × 10⁻⁴, the pH is calculated as 2.7.
• 😀 Example 2: For a 0.1 M NH₄OH solution with a degree of ionization of 0.01, the pH is calculated as 11.
• 😀 pH calculations for weak acids and bases often involve square roots and logarithmic functions.
• 😀 To find the molarity of an acid like acetic acid, you can use the formula: [Acid] = (H⁺ concentration)² / Ka.
• 😀 For a more complex problem, like determining the mass of acetic acid needed for a solution, you calculate its molarity and multiply by the molar mass and volume.

Q & A

What are weak acids and weak bases?

Weak acids and weak bases are substances that do not fully dissociate in water. For weak acids, the dissociation constant (Ka) represents their ionization in solution, while weak bases have a base dissociation constant (Kb). Examples include acetic acid (CH3COOH) for weak acids and ammonia (NH3) for weak bases.

How do you calculate the pH of a weak acid?

To calculate the pH of a weak acid, you first calculate the concentration of hydrogen ions (H+) using the formula: [H+] = √(Ka × C), where Ka is the acid dissociation constant and C is the concentration of the acid. Then, calculate the pH using the formula pH = -log[H+].

What is the formula for calculating the pH of a weak base?

For a weak base, the concentration of hydroxide ions (OH-) is calculated using the formula: [OH-] = √(Kb × C), where Kb is the base dissociation constant and C is the concentration of the base. The pH is then found using the relationship pH = 14 - pOH, where pOH = -log[OH-].

Why is HF considered a weak acid?

HF (hydrofluoric acid) is considered a weak acid because it does not completely dissociate in water. It has a relatively small dissociation constant (Ka), meaning only a small fraction of HF molecules ionize to release hydrogen ions (H+).

How do you calculate the pH of a 0.001 M HF solution with a Ka of 4 × 10^-4?

To calculate the pH of the HF solution, first calculate the concentration of H+ using the formula: [H+] = √(Ka × C) = √((4 × 10^-4) × 0.001) = 2 × 10^-3. Then, calculate the pH: pH = -log(2 × 10^-3) = 2.7.

How do you calculate the pH of a weak base like ammonia (NH3)?

For a weak base like ammonia, first calculate the concentration of OH- using the formula: [OH-] = √(Kb × C). For ammonia, with Kb = 1 × 10^-5 and C = 0.1 M, you get [OH-] = 3.16 × 10^-3. Then, calculate the pOH: pOH = -log(3.16 × 10^-3) = 2.5. Finally, calculate the pH: pH = 14 - pOH = 14 - 2.5 = 11.5.

What does the formula [OH-] = √(Kb × C) help to determine?

The formula [OH-] = √(Kb × C) helps to determine the concentration of hydroxide ions (OH-) in a solution of a weak base. This concentration is then used to calculate the pH by finding the pOH and subtracting it from 14.

How is the mass of acetic acid (CH3COOH) determined for a given pH solution?

To determine the mass of acetic acid needed for a solution with a specific pH, first calculate the molarity of the acid using the given pH and dissociation constant (Ka). Then, use the formula m = (Molarity × Molar Mass × Volume) to find the mass required.

How do you calculate the molarity of acetic acid from pH?

From the pH, you can calculate the concentration of hydrogen ions (H+) using the equation [H+] = 10^(-pH). Then, use the formula for weak acids [H+] = √(Ka × C) to solve for C, the molarity of acetic acid.

What is the molarity and mass of acetic acid required to prepare a 100 mL solution with a pH of 3?

For a pH of 3, the concentration of H+ is 10^-3 M. Using the formula [H+] = √(Ka × C) with Ka = 2 × 10^-4, we find that the molarity (C) of acetic acid is 5 × 10^-3 M. To prepare 100 mL of this solution, the mass required is calculated as 0.03 grams.