Assembling and Using an LED-Based Detector To Monitor Absorbance Changes during Acid–Base Titrations

Abstract

A simple photometric assembly based in an LED as a light source and a photodiode as a detector is proposed in order to follow the absorbance changes as a function of the titrant volume added during the course of acid−base titrations in the presence of a suitable visual indicator. The simplicity and low cost of the electronic device allow the students to easily assemble the photometer and use it as a titration detector. The choice of the appropriate LED color should also demonstrate the principles of complementary colors. Concepts of data handling and relationship between the pH of the titration end point and indicator choice can be addressed. Errors associated with the use of wrong indicators can be demonstrated. The circuit assembly can highlight for the students the instrumentation and automation importance in modern chemical analysis. The discussion can be extended to relevant issues involved in this matter, such as light absorption, circuit analysis, and the hydrolysis concept, once they are involved and are closely related with the results obtained.

Review of Student-Built Spectroscopy Instrumentation Projects

“…Four main types of low-cost, solid state light detectors are available: LEDs, ,− ,,, photodiodes, ,,,,,− light dependent resistors (LDRs, also known as photocells or photoresistors), ,,,,,,,,,,,,,,− and phototransistors. , The first option, an LED, is commonly used as a light source in the emission mode; however, forward biased LEDs can be repurposed as detectors for light of slightly higher energy than the light they emit (Figure b). − When such light strikes the LED, a photocurrent is generated . This effect is useful to detect a narrow band of wavelengths since the LED responds only to wavelengths just below its emission maximum .…”

“…Absorbance spectroscopy is a widely used technique that is applicable to many analytes, but popular samples for visible absorbance measurements include brightly colored metal salts (such as Co­(II), Cu­(II), and Ni­(II), which form colored complexes in aqueous solution) and strongly absorbing organic indicators and dyes (Table ), including common food colorings (such as Red 40, Yellow 5, and Blue 1) that are compatible with remote instruction. Simple experiments ask students to develop the Beer’s law relationship showing the linear relationship between absorbance and concentration or path length. ,,,,, More involved experiments may require students to perform a kinetic analysis, ,,,, complete a photometric titration, ,, detect analytes in eluent using a flow cell, or compare their devices to commercial instrumentation. Many student-built systems are suitable for quantitative analysis and produce results that compare favorably with those from more expensive instruments.…”

An accurate, precise, and affordable light emitting diode spectrophotometer for drinking water and other testing with limited resources

“…Educators and their students at the high school, college, and university levels often build simple LED spectrophotometers as part of the chemistry, physics, or electronics curriculum [8][9][10][11][12][13][14][15][16]. These simple LED spectrophotometers are very useful for education; however, they usually have simple power, source, and signal conditioning circuits, which limit their performance.…”

Constructing an Electronic Calorimeter That Students Can Use to Make Thermochemical and Analytical Determinations during Laboratory Experiments

“…One of the most interesting and useful areas in General Chemistry is the development of electronic instruments, especially taking into account the impact that electronics have on current students. In recent years (2013–2019) various Arduino-based projects have been appearing in a timely manner, that are continuously increasing, including different proposals for the teaching of chemistry − (see Figure ). These works perform experiments in a creative and economical way both at the university level and in secondary education.…”

“…For instance, with regard to analytical chemistry the construction of instruments to measure analytical parameters such as absorbance is described in McClain 2014 . In addition, the construction of instruments to measure air quality or electronic burets is also described in the literature. , The ascending trend of Arduino keyword appearances in conference and indexed journal manuscript titles over time (see Figure ) suggests that the number of publications related to Arduino technology will gradually increase, given the multiple educational benefits that these projects bring.…”