Q8(a)(ii). Fraction of fully deprotonated EDTA
EDTA is a hexaprotic system, designated as H₆Y²⁺. At pH 6.00 and at a formal concentration of 0.10 M, the composition of an EDTA solution is found to be as follows: [H₆Y²⁺] = 8.4 × 10⁻²⁴ M; [H₅Y⁺] = 8.4 × 10⁻¹⁴ M; [H₄Y] = 2.7 × 10⁻⁹ M; [H₃Y⁻] = 2.7 × 10⁻⁵ M; [H₂Y²⁻] = 0.059 M; [HY³⁻] = 0.041 M and [Y⁴⁻] = 2.3 × 10⁻⁶ M. Find the fraction of EDTA in the form Y⁴⁻.
Answer in brief
αY⁴⁻ = [Y⁴⁻]/C(EDTA) = 2.3 × 10⁻⁵, or 0.0023%.
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Coversfraction of Y4-alpha Y4- EDTAconditional formation constantEDTA speciationhexaprotic EDTA
All parts of Question 8
- 8(a)(i) Cyanide determination with silver nitrate10 marks
- 8(a)(ii) Fraction of fully deprotonated EDTA5 marks
- 8(b) Total hardness of water by EDTA15 marks