Assume that a sample of water contains 25 mg/L of N(CH2CO2Na)3, the trisodium NTA salt, formula weight 257. The total concentration of both complexed and uncomplexed NTA is 9.7 ´ 10-5 mmol/mL. Assuming a system in which NTA at
pH 8.00 is in equilibrium with solid Pb(OH)2, the NTA may be primarily in the uncomplexed form, HT2-, or in the lead complex, PbT -. The predominant speciesmay be determined by calculating the [PbT- ]/[HT2-] ratio from the expression for K,noting that at pH 8.00, [OH-] = 1.00 ´ 10-6 M