1. Introduction

It has been shown that teaching chemistry is not very popular. In fact it could be irrelevant in the eyes of students which find it difficult to learn [1-4]. Therefore, it is essential to combine the teaching of chemistry with experiments that grab students’ attention and excite them about the subject. In third world countries the problem is exacerbated by the need for cheap equipment given low budgets and scarce resources [5]. Furthermore, environment pollution is also a growing concern causing a lot of problems in the world. Thus, school chemical experiments should be arranged in a way that is safer for the environment. Students also should be sensitive to what will be left after these experiments as waste. It is to be hoped that as a result, this will become a habit for their daily activities as well.

In this regards, one of the useful experiment is microfluidic analysis. Microfluidics is the science and technology of systems that process or manipulate small amounts of fluids using channels with dimensions of tens to hundreds of micrometer [6]. Unfortunately this work is not well known among high school teachers. There are reports for different paper-based microfluidic analytical devices (μPADs) in literature [7-10] but the cheapest and easiest one is recommend by Wang and at al., [11-13] which can be used in high school chemistry laboratories. The main advantage of this method is showing chemistry in real life with simple equipment and using very small amount of compounds.

Colorimeter and determination of ion concentration in unknown samples is one of the popular undergraduate laboratory works in universities. Whereas doing so in high school, requires expensive spectroscopy equipment. Potentially, this can be achieved using a form of colorimetry in which comparisons of depth of color are made by eyeballing without necessarily using a colorimeter [15]. In this method, a set of solutions will be prepared and the color of the unknown tube will be compared with them in order to find which matches best. Kohl et al. [22] used digital images of solutions (food dye, sports drinks, and Iron chloride). Kuntzleman at el. [25] left samples in a cardboard box, allowed light to pass through it, and used a cell phone as the light detector. Moreover, Rice at el. [23] also used a cell phone camera as a simple, low cost experimental technique for teaching molecular diffusion.

We tried to repeat nitrite ion determination with a paper microfluidic device which Wang and et al [11] proposed. However, we encountered two main problems. First, N-(1-naphthyl) - ethylene diamine and p-amino benzene sulfonamide which are used as mixed indicators for the nitrite ion, were not familiar to high school students. Second, preparing these compounds was not so easy. Therefore, we decided to use the method for iron ion determination in an iron tablet.

The body relies on the iron ion in order to produce hemoglobin, a protein which helps red blood cells deliver oxygen throughout the body. Furthermore, iron deficiency can lead to anemia. It is the most common nutritional deficiency in the world, and women are among those at greatest risk. By doing this experiment, as well as teaching chemistry concepts, we also wanted to achieve two goals: first, we wanted to emphasize using minimum amounts of compounds and therefore produce less waste, second; we wanted to explain the importance of iron tablet intake for women.

4,7-diphenyl-1,10-phenanthroline reacts with Fe²⁺ forming a complex with a deep red color which absorbs light at wavelength 533 nm and can be used to illustrate the Beer–Lambert Law [14]. 4,7-diphenyl-1,10-phenanthroline is not familiar for high school student, therefore the iron (II) in sample and known solutions was converted to iron (III) by potassium permanganate in an acidic solution which then turned into a red color by a potassium thiocyanate solution. A camera-phone was used as the detector for the assay.

In the next experiment, the concentration of an unknown copper (II) ion was determined by a set of known concentrations and their color changes after using an ammonia solution. Ammonia evaporates after the solution dries, therefore, instead of a paper microfluidic device, a simple plastic sheet was used [5]. Again, a camera-phone is used as the detector for this assay. These two experiments are very simple and data collection is fast and easy. It can be done in all high school laboratories.

2. Materials

The unknown sample was an iron tablet which was manufactured by Rouz Darou laboratories in Tehran. A Whatman filter paper was used. Drawing a circle by a permanent marker pen on the filter paper made hydrophobic barriers constraining the reactions in defined areas. A camera–phone was used to capture images of reaction and the Adobe Photoshop 7.0 ME software was employed to get the gray values of the detection areas from the collected images.

2.1. Fabrication of the Paper-Based Device

As Wang and et al. recommended, a filter paper (Whatman No.1) was used. This provides a good medium for the colorimetric reaction to take place. Filter papers were placed into a dry glass petri dish in a fume hood; a solution of potassium thiocyanate was poured into the dish to completely soak the papers. The papers were taken out and left in the hood for an hour to become dry. With a permanent marker, six circles were drawn onto the dried filter paper (Figure 1).

Figure 1. Drawing a Pattern in filter paper

2.2. Sample Preparation

Standard solutions with concentrations of 0.020, 0.016, 0.012, 0.008 and 0.004 mol.L^-1 were prepared from solid iron (II) sulfate heptahydrate (FeSO₄.7H₂O M = 278.0146 g / mole) by dissolving 0.278 g in a 50 mL volumetric flask (solution A). Students were required to dilute this solution following the procedures described in table 1 and calculate the molarity of each test tube. An iron tablet was carefully weighed and its color peel was removed with a sharp knife. The white tablet was then grinded in a mortar and dissolved into a 50 mL volumetric flask (solution B).

Table 1. Preparing solutions in test tube

2.3. Procedures for Determination of Iron Ions

Using a clean dropper the solution of each test tube with known concentration was carefully dropped onto six outer circles. The same volume of tablet solution was dropped onto the central circle. After a few seconds, an image was captured by a camera phone.

Figure 2. The relationship between percentage of grayscale and iron concentration

2.4. Procedures for Determination of Copper (II) Ions

Standard solutions with concentrations of 0.04, 0.032, 0.024, 0.016 and 0.008 mol.L^-1 were prepared from solid copper (II) sulfate pentahydrate (CuSO₄.5H₂O M = 249.5 g / mole) by dissolving 0.249 g in a 25 mL volumetric flask (solution A). Students were required to dilute this solution similar to what is described in table 2 and by using a dropper, and then calculate the molarity of solution in each watch glass. One mL of solution is equal to 25 drops. In addition, a solution with unknown concentration was given to students.

Table 2. Preparing solutions in watch glasses

Six circles were drawn onto a paper and it was placed under a plastic cover. Two drops of each solution was added to corresponding numbers. (Figure 3).

Figure 3. Drops of solutions on a sheet of plastics

2 drops of Ammonia solution was carefully dropped onto the central each circles. After a few seconds, an image was captured by a camera phone (figure 4).

Figure 4. Copper solutions with ammonia

3. Results

According to figure 2, the relation between the concentration of the iron ion and the intensity of the gray color is linear with the correlation coefficient 0.909 and standard error of the estimation 3.5777. The linear equation was expressed as y = 1550x + 38.6 where x represents the iron ion concentration (mol. L^-1), and y represents the gray value (%). By using this data, the concentration of iron ion was found to be 0.017 mol. L^-1 in tablet sample, which means there is 47.6 mg Fe²⁺ in each tablet. The 4.8% difference between the written value in tablet box and the experimentally determined iron ion concentration is readily rationalized given the approximations implicit to this methodology.

The equation for copper ion concentration was expressed as y = 1100x + 38.4 where x represents the copper ion concentration (mol. L^-1), and y represents the gray value with the correlation coefficient 0.989 and standard error of the estimation 1.673.

4. Hazards

The potassium thiocyanate solution is toxic and should be used only in a chemical fume hood. It can be absorbed through the skin. Potassium thiocyanate is a skin and eye irritant and is toxic when ingested. Eye contact will cause redness and pain. Skin contact will cause localized irritation. Ingestion will cause headache, nausea, vomiting, dizziness and faintness [16-19].

Potassium permanganate solution can cause skin irritation. Flush with water immediately [20].

5. Conclusions

It is obvious that teaching chemistry with experiments increases enthusiasm and motivation among students. In most high schools in developing countries there are not enough facilities to achieve this goal; therefore in this article we proposed two simple experiments: paper-based microfluidic analytical devices for iron ion detection and plastic sheet instead of microplate for copper ion detection. All the equipment are simple and easy to use. Furthermore the experiment reduces disposal and students learn more about protecting the environment. Above all, by doing this experiment, as well as teaching chemistry concepts, the importance of iron tablet intake will be explained.

ACKNOWLEDGEMENTS

Special thanks are owed to the principle of the beheshty high school in Karaj for facilitating access to laboratory supplies.