【Daily Question】Chemical Engineering Principles 410: Metal Indicators (August 19)
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This post was last edited by Zaihui Kangqiao on 2016-8-30 at 09:37. The Chemical Engineering Theory section is now launching a \"One Question per Day\" activity to help everyone reinforce their basic knowledge in chemical engineering. Subsequent series such as \"Chemical Engineering Principles\", \"Mass Transfer and Separation\", \"Chemical Engineering Thermodynamics\", and \"Chemical Engineering Processes\" will be introduced as well; we hope everyone will give it their active support~ Wishing everyone a happy Christmas~~ Answers to the questions in the \"One Question per Day\" activity can be viewed directly, and the thread will be closed after 1 day! ! To encourage everyone’s continued participation this year! Participation earns 3 wealth points, with an additional 4 wealth points for correct answers~~~ Short answer: Why can metal indicators change color? Answer: A metal indicator is a chelating agent that forms colored complexes with the metal ions being titrated; the color of these colored complexes differs from the color of the indicator itself.
When a metal indicator reacts with metal ions, it forms a complex that has a color significantly different from that of the indicator itself. If M represents the metal ion and In represents the metal indicator, then: M + In (color A) ⇌ MIn (color B). Since the complex formed between the metal ion and the metal indicator is less stable than the complex formed between the metal ion and the chelating agent EDTA, at the endpoint, the metal ion that is bound to the indicator is displaced by EDTA, releasing the indicator and causing a sudden change in the color of the solution, thereby indicating the arrival of the titration endpoint. At this point, what we see is the mixed color of the indicator and the solution: MIn (yellow color) + H2Y2— MY2— + In (red color) + 2H+
Why can metal indicators change color? Answer: Since the metal indicator itself is a weak acid and exhibits an acid effect, the conditional stability constants of the complex formed between the indicator and M vary at different pH levels, which leads to color changes.
Metal indicators are mostly organic dyes that can form colored complexes with certain metal ions; the color of these complexes differs from that of the metal indicator.
Since the metal indicator itself is a weak acid and exhibits an acid effect, the conditional stability constants of the complex formed between the indicator and M vary at different pH levels, which results in different pM values for the color change point; in other words, there is no fixed color change point.
A metal indicator is a chelating agent that forms colored complexes with the metal ions being titrated; the color of these colored complexes differs from the color of the indicator itself.
A metal indicator is a chelating agent whose color differs when it binds to a metal and when it is not bound to any metal. Taking the binding of Eriochrome Black T with magnesium ions as an example, Eriochrome Black T itself is in the blue HIn2- form; after binding with magnesium, it forms MgIn-, which is red in color.
A metal indicator is a chelating agent whose color differs when it binds to a metal and when it is not bound to any metal. Taking the binding of Eriochrome Black T with magnesium ions as an example, Eriochrome Black T itself is in the blue HIn2- form; after binding with magnesium, it forms MgIn-, which is red in color.
A metal indicator is a chelating agent that forms colored complexes with the metal ions being titrated; the color of these colored complexes differs from the color of the indicator itself.