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Ions as Acids and Bases

Ions as Acids and Bases

Salts with Acidic Ions
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:

Indicators

Indicators

Certain organic substances change color in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenolphthalein is a colorless substance in any aqueous solution with a hydronium ion concentration greater than 5.0 × 10−9 M (pH < 8.3). In more basic solutions where the hydronium ion concentration is less than 5.0 × 10−9 M (pH > 8.3), it is red or pink. Substances such as phenolphthalein, which can be used to determine the pH of a solution, are...

Metal-Ligand Bonds

Metal-Ligand Bonds

The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
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Formation of Complex Ions

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A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...

Alkali Metals

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Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the alkali metals are unusually low for metals and decrease going down the group, while the density increases going down the group with the exception of potassium (Table 1).
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Related Experiment Video

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Quantification of Heavy Metals and Other Inorganic Contaminants on the Productivity of Microalgae

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Published on: July 10, 2015

Triple-Indicator-Based Multidimensional Colorimetric Sensing Platform for Heavy Metal Ion Detections.

Noorhayati Idros^1,2, Daping Chu¹

¹Centre for Photonic Devices and Sensors, Department of Engineering , University of Cambridge , Cambridge CB3 0FA , United Kingdom.

|September 8, 2018

Summary

This study introduces a low-cost paper-based microfluidic analytical device (μPAD) for detecting toxic heavy metals like mercury and lead in water. The portable device offers a simple, visual method for environmental and public health monitoring.

Keywords:

color calibration heavy metals multidimensional sensing paper-based microfluidics triple indicator

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Area of Science:

Environmental Science
Analytical Chemistry
Materials Science

Background:

Heavy metal pollution poses significant environmental and public health risks globally.
Current detection methods are costly, require specialized labs, and are time-consuming.
There is a need for accessible, portable, and rapid heavy metal detection techniques.

Purpose of the Study:

To develop a low-cost, paper-based microfluidic analytical device (μPAD) for monitoring multiple heavy metal ions.
To enable facile, portable, and disposable detection of toxic metals in environmental samples.
To provide a sensitive and accurate alternative to conventional laboratory-based methods.

Main Methods:

Utilized preloaded triple indicators or ligands on μPADs for colorimetric detection of metal ions.
Employed digital imaging and RGB color space analysis for quantitative color feature assessment.
Validated the device's performance using real water samples for simultaneous detection and discrimination.

Main Results:

The μPAD successfully detected and discriminated between various heavy metal ions (Hg, Pb, Cr, Ni, Cu, Fe) with high accuracy.
Colorimetric changes were observable by the naked eye and quantitatively analyzed.
Achieved sensitivity below safe limit concentrations with a controlled error range.

Conclusions:

The developed μPAD offers a promising, cost-effective solution for portable heavy metal monitoring.
This technology facilitates on-site, semiquantitative, and qualitative analysis of water quality.
The device has significant potential for widespread application in environmental surveillance and public health protection.