Residual method titration with disodium edetate VS is applicable to what metal ion:

Residual method titration with disodium edetate VS is applicable to what metal ion:

• A. Aluminum
• B. Calcium
• C. Zinc
• D. Magnesium

Answer: (A)

The idea behind the residual (back) titration with EDTA is to determine a metal by first adding an excess of EDTA to the sample, then titrating the remaining EDTA with a standard solution. The amount of metal in the sample is inferred from how much EDTA was consumed by that metal. This approach is especially useful when a direct EDTA titration is problematic due to precipitation, hydrolysis, or interference, and when the target metal forms a stable, well-behaved complex with EDTA under controlled conditions. Aluminum fits this situation well. Al3+ tends to hydrolyze and form insoluble species at certain pH ranges, making direct titration tricky. By using conditions that keep aluminum in solution and form a strong Al–EDTA complex, the residual method allows an accurate determination by measuring the EDTA that remains unbound after all aluminum has complexed. The strong affinity between aluminum and EDTA also helps produce a clean endpoint in back-titration. Other ions like calcium and magnesium are more commonly determined by direct EDTA titration at higher pH with an appropriate indicator, because their chemistry with EDTA under those conditions is straightforward and precipitation issues are less problematic. Zinc can be titrated with EDTA as well, but back-titration is not the standard approach for it in everyday practice.

The idea behind the residual (back) titration with EDTA is to determine a metal by first adding an excess of EDTA to the sample, then titrating the remaining EDTA with a standard solution. The amount of metal in the sample is inferred from how much EDTA was consumed by that metal. This approach is especially useful when a direct EDTA titration is problematic due to precipitation, hydrolysis, or interference, and when the target metal forms a stable, well-behaved complex with EDTA under controlled conditions.

Aluminum fits this situation well. Al3+ tends to hydrolyze and form insoluble species at certain pH ranges, making direct titration tricky. By using conditions that keep aluminum in solution and form a strong Al–EDTA complex, the residual method allows an accurate determination by measuring the EDTA that remains unbound after all aluminum has complexed. The strong affinity between aluminum and EDTA also helps produce a clean endpoint in back-titration.

Other ions like calcium and magnesium are more commonly determined by direct EDTA titration at higher pH with an appropriate indicator, because their chemistry with EDTA under those conditions is straightforward and precipitation issues are less problematic. Zinc can be titrated with EDTA as well, but back-titration is not the standard approach for it in everyday practice.