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0.310 M Nh4 2so4 and 0.492 M Nh3 Calculate Oh

Reviewed by Calculator Editorial Team

This calculator determines the hydroxide ion (OH-) concentration in a solution containing ammonium sulfate (NH4 2SO4) and ammonia (NH3). The calculation uses the Henderson-Hasselbalch equation and assumes standard conditions.

How to Calculate OH- Concentration

The hydroxide ion concentration in a buffer solution can be calculated using the Henderson-Hasselbalch equation. For a solution containing NH4 2SO4 and NH3, the calculation involves:

  1. Determining the pKa of the weak base (NH3)
  2. Calculating the ratio of conjugate base to weak base concentrations
  3. Solving for pOH and then converting to OH- concentration

Note: This calculation assumes standard temperature and pressure conditions (25°C, 1 atm). For accurate results, verify your solution's temperature and pressure.

The Formula Explained

The Henderson-Hasselbalch equation for this system is:

pOH = pKa + log10([NH3]/[NH4+])

Where:

  • pOH = -log10([OH-])
  • pKa = acid dissociation constant of NH3 (approximately 9.25 at 25°C)
  • [NH3] = concentration of ammonia (0.492 M in this case)
  • [NH4+] = concentration of ammonium ion (0.310 M in this case)

Once pOH is calculated, the OH- concentration can be found using:

[OH-] = 10-pOH

Worked Example

Let's calculate the OH- concentration for a solution with [NH4 2SO4] = 0.310 M and [NH3] = 0.492 M:

  1. First, note that NH4 2SO4 dissociates completely to give NH4+ and SO4 2-
  2. Calculate the ratio [NH3]/[NH4+] = 0.492/0.310 ≈ 1.587
  3. Using pKa = 9.25: pOH = 9.25 + log(1.587) ≈ 9.25 + 0.200 ≈ 9.450
  4. Convert to OH- concentration: [OH-] = 10-9.450 ≈ 3.55 × 10-10 M

This means the solution has a hydroxide ion concentration of approximately 3.55 × 10-10 M.

Frequently Asked Questions

What is the difference between NH4 2SO4 and NH3 in this calculation?

NH4 2SO4 provides NH4+ ions which act as a weak acid, while NH3 acts as a weak base. The ratio of these two species determines the buffer's pH.

Why is the pKa value important in this calculation?

The pKa value represents the acid dissociation constant of NH3, which is crucial for determining the buffer's effectiveness and the resulting pH.

How does temperature affect this calculation?

The pKa value changes with temperature. For precise calculations, use temperature-adjusted pKa values or account for the temperature effect in your calculations.