根据括号内数据,为了配制 pH = 7 的缓冲溶液,最合适的缓冲对: [ K a θ ( HAc ) = 1.8×10 - 5 , K b θ (NH 3 ) = 1.8×10 - 5 , K a 1 θ ( H 2 CO 3 ) = 4.2 × 10 - 7 , K a 2 θ ( H 2 CO 3 ) = 5.6 × 10 - 11 , K a 1 θ ( H 3 PO 4 ) = 7.6 × 10 - 3 , K a 2 θ ( H 3 PO 4 ) = 6.3 × 10 - 8 , K a 3 θ ( H 3 PO 4 ) = 4.4 × 10 - 13 ]