JEE Main Chemistry question
pH of 0.1 M Na₂HPO₄ and 0.2 M NaH₂PO₄ solutions are respectively. pKa for H₃PO₄ are 2.12, 7.21 and 12.0 for respective dissociation to H₂PO₄⁻, HPO₄²⁻ and PO₄³⁻.
Answer: (B)
Solution
pH(HPO₄²⁻)≈½(pKa2+pKa3)=9.61; pH(H₂PO₄⁻)≈½(pKa1+pKa2)=4.67.