Calculate Ph of 0.1 M Nahco3

What is pH?

The pH scale measures how acidic or basic a solution is. It ranges from 0 to 14, where:

• pH 0-6 is acidic
• pH 7 is neutral
• pH 8-14 is basic

The pH is calculated using the hydrogen ion concentration [H⁺] with the formula:

For weak acids like NaHCO3, the pH cannot be calculated directly from the concentration alone and requires additional information about the dissociation constant.

How to Calculate pH

Calculating the pH of a NaHCO3 solution involves several steps:

1. Determine the dissociation constant (K_a) of NaHCO3
2. Calculate the concentration of H⁺ ions using the Henderson-Hasselbalch equation
3. Convert the H⁺ concentration to pH using the pH formula

The Henderson-Hasselbalch equation is particularly useful for weak acids:

Where:

• pK_a is the negative logarithm of the acid dissociation constant
• [A⁻] is the concentration of the conjugate base (HCO₃⁻)
• [HA] is the concentration of the weak acid (NaHCO3)

pH of NaHCO3 Solutions

Sodium bicarbonate (NaHCO3) is a weak acid with a pK_a of approximately 6.35. When dissolved in water, it dissociates partially:

The pH of a NaHCO3 solution depends on its concentration and the amount of dissociation. For a 0.1 M NaHCO3 solution:

• The initial concentration of NaHCO3 is 0.1 M
• The concentration of HCO3⁻ is initially 0 M
• The pH is determined by the equilibrium between NaHCO3 and HCO3⁻

Example Calculation

Let's calculate the pH of a 0.1 M NaHCO3 solution step by step:

1. Start with the Henderson-Hasselbalch equation:
   pH = pK_a + log₁₀([HCO3⁻]/[NaHCO3])
2. Assume the solution is at equilibrium where [HCO3⁻] = x and [NaHCO3] = 0.1 - x
3. For a weak acid, the initial concentration is approximately equal to the undissociated acid concentration at low concentrations
4. Using pK_a = 6.35 and [NaHCO3] ≈ 0.1 M:
   pH = 6.35 + log₁₀([HCO3⁻]/0.1)
5. At equilibrium, [HCO3⁻] ≈ 0.01 M (from dissociation calculations)
6. Plugging in the values:
   pH = 6.35 + log₁₀(0.01/0.1) = 6.35 + log₁₀(0.1) = 6.35 - 1 = 5.35

Therefore, the pH of a 0.1 M NaHCO3 solution is approximately 5.35.