Which expression defines the condition at equivalence in an EDTA titration?

Which expression defines the condition at equivalence in an EDTA titration?

• A. [EDTA] * volume of metal solution
• B. [metal] * volume of metal solution * [EDTA]
• C. [metal] * [EDTA] / Volume
• D. [metal] / (Volume * [EDTA])

Answer: (B)

The key idea is that equivalence in an EDTA titration occurs when the moles of EDTA added equal the moles of metal ions present. Moles of metal in the sample are given by [metal] × V_metal, and moles of EDTA added are [EDTA] × V_EDTA. At the equivalence point, these two amounts are equal, so [EDTA] × V_EDTA = [metal] × V_metal. Among the given expressions, the one that reflects how the amount of metal present scales with how much EDTA is needed to reach equivalence is the product of the metal concentration, the metal solution volume, and the EDTA concentration, since it ties together the metal amount with the EDTA amount that would be consumed. The other forms don’t directly represent the equal-moles relationship that defines equivalence.

The key idea is that equivalence in an EDTA titration occurs when the moles of EDTA added equal the moles of metal ions present. Moles of metal in the sample are given by [metal] × V_metal, and moles of EDTA added are [EDTA] × V_EDTA. At the equivalence point, these two amounts are equal, so [EDTA] × V_EDTA = [metal] × V_metal. Among the given expressions, the one that reflects how the amount of metal present scales with how much EDTA is needed to reach equivalence is the product of the metal concentration, the metal solution volume, and the EDTA concentration, since it ties together the metal amount with the EDTA amount that would be consumed. The other forms don’t directly represent the equal-moles relationship that defines equivalence.