COMEDK202510 May 2025Evening ShiftChemistryIonic EquilibriumActual
The ionisation constant of the weak acid HF whose concentration is 0.1 M is 3.5 10⁻⁴ . The Equilibrium constant value for the reaction F ^- + H ₂ O HF + OH ^- is _____ and the pH of aqueous solution of the weak acid is _____.
Options
- AK _ eq =3.58 10⁻¹¹ ~ &~ pH =4.19
- BK _ eq =3.92 10⁻¹⁰ ~ &~ pH =4.07
- CK _ eq =2.86 10⁻¹¹ ~ &~ pH =2.23
- DK _ eq =4.4 10⁻¹¹ ~ &~ pH =4.25
Correct answer
C. K _ eq =2.86 10⁻¹¹ ~ &~ pH =2.23
Step-by-step solution
The reaction F^- + H₂O HF + OH^- is hydrolysis of the conjugate base, so K_ eq = K_b = K_w K_a : K_ eq = 1.0 10⁻¹⁴ 3.5 10⁻⁴ 2.86 10⁻¹¹ For pH, using [H^+] K_a C : [H^+] = 3.5 10⁻⁴ 0.1 = 3.5 10⁻⁵ 5.92 10⁻³ M pH = - (5.92 10⁻³) 2.23