A scientist determines how hard the tap water is in the laboratory, using an EDTA titration. If the pipes in the building are old and some rust dissolves into the tap water. how will the results of the test change?
A. The results will not change because the EDTA titra- tion only works with Ca2+ and Mg2+.
B. The titration will not be able to be carried out be- cause the tap water will be colored.
C. The tap water will appear to have less Ca2+ and Mg2+ present.
D. The tap water will appear to have more Ca2+ and Mg2+ present.
* For this answer, would the answer be D since the rust could contain other cations such as iron for the EDTA to attach to?
Yes, you are correct. The answer would be D. The tap water will appear to have more Ca2+ and Mg2+ present.
During an EDTA titration, EDTA (ethylene-diamine-tetraacetic acid) is added to the tap water sample. The EDTA molecule forms stable complexes with metal cations such as Ca2+ and Mg2+. However, if there are other cations present in the tap water, such as iron (Fe2+ or Fe3+), the EDTA can also form complexes with these cations.
When rust dissolves into the tap water due to old pipes, it introduces iron cations into the sample. These iron cations can also react with the EDTA, resulting in a higher total metal ion concentration being titrated. Therefore, the tap water will appear to have more Ca2+ and Mg2+ present, making option D the correct choice.