\( K_a \) for \( \mathrm{CH_3COOH} \) is \( 1.8 \times 10^{-5} \) and \( K_b \) for \( \mathrm{NH_4OH} \) is \( 1.8 \times 10^{-5} \). The \( \mathrm{pH} \) of ammonium acetate solution will be ______.
