Assume the tap water to be analyzed contains a certain amount of unknown cation
ID: 988318 • Letter: A
Question
Assume the tap water to be analyzed contains a certain amount of unknown cation which forms complex with EDTA at pH but not at pH 12. The formation constant for the EDTA complex of this unknown cation a, pH 10 is 1 Times 10^13. The formation constant for Ca^2+ is 5 Times 10^10 and for Mg^2+ 5 Times 10^8. Neither EBT or Calcon indicator are affected by the presence of this cation. Note that Calcon is used to find the concentration of Ca at a pH or 12 and EBT is often used to find the concentration of Ca and Mg ions as a set (hardness) at pH 10. How would the value of the concentration of Ca and Mg ions determined be affected by the presence of this unknown cation impurity? Explain your answer.Explanation / Answer
although the formation constant of the complex with the unknown ion is smaller than the complexation of calcium and magnesium, if the hardness determination is made at pH 10, the value will be wrong by the interaction of the cation with the environment increasing the hardness results in the determination, that is, the concentration of calcium and magnesium will result greater than the real, by the interference ion.