Chemistry
Chemistry
Problem
Equal volumes of 0.100 M hydrofluoric acid (HF, Ka = ) and 0.100 M ammonia (NH₃, Kb = ) are mixed at 25 °C. Calculate the pH of the final solution.Intuitive explanation
When equal volumes of a weak acid and weak base mix, you're creating a competition between two equilibria. The key is recognizing that HF and NH₃ will react together to form their conjugate pairs (F⁻ and NH₄⁺), and then you need to determine which conjugate is stronger—that will dominate the final pH. Compare the acid strength of NH₄⁺ to the base strength of F⁻ using their Ka and Kb values to predict whether the solution ends up acidic or basic.
Intuitive explanation
When equal volumes of a weak acid and weak base mix, you're creating a competition between two equilibria. The key is recognizing that HF and NH₃ will react together to form their conjugate pairs (F⁻ and NH₄⁺), and then you need to determine which conjugate is stronger—that will dominate the final pH. Compare the acid strength of NH₄⁺ to the base strength of F⁻ using their Ka and Kb values to predict whether the solution ends up acidic or basic.