Data & Experiment

To quantify the effectiveness of the ion exchange resin, we conducted an experiment measuring the Ca²⁺ concentration and pH of tap water and DI water before and after passing through a charged ion exchange resin.

1. Pour EWS ion exchange resin product into a buret. Charge it by submerging the resin in 3M HCl for ~20 minutes.
2. Once sufficiently charged, drain out HCl and dispose of it in a hazardous-waste container. Rinse with DI water 1–2 times.
3. Calibrate the Ca²⁺ probe using 100 mg/L and 1000 mg/L Ca²⁺ standards.
4. Measure 100 mL of tap water in a beaker. Record Ca²⁺ and pH values.
5. Flush the tap water through the buret and measure again.
6. Repeat 3 times for tap water and DI water respectively.

Water hardness, defined by Ca²⁺ and Mg²⁺ content, causes mineral deposits that block pipelines and reduce heat-exchanger efficiency. In Utah, hardness can exceed 500 PPM in some cities [1]. Ion exchange removes Ca²⁺ via resins such as Amberlite, containing sulfonic acid groups (–SO₃H) [2]. Charging with HCl replaces Na⁺ with H⁺; during treatment, Ca²⁺ ions in water are exchanged for H⁺ ions. We examined the EWS resin's ability to remove Ca²⁺ from Utah tap water using ion-selective and pH electrodes. DI water served as control. A qualitative soap test also distinguishes hard vs soft water: Ca²⁺ forms insoluble scum with soap in hard water, while soft water produces suds.

From experimental methods, we measured Ca²⁺ concentration (mg/L) of Utah water before and after EWS resin treatment as an indicator of water softening efficacy. These measurements occurred 3 times each for Utah tap water and distilled (DI) water (Fig. 1). Regarding tap water, initial Ca²⁺ concentrations ranged from ~46-50 mg/L, consistent with the expected range of Salt Lake City water hardness measurements. Post-treatment Ca²⁺ levels dropped to nearly 0 mg/L by a significant amount -- likely surpassing the limit of detection (LOD) of the ion-selective electrode. Despite this, the significant change in concentration suggests effective Ca²⁺ removal by the EWS resin.

Furthermore, we have measured the pH before and after treatment as an indication of H⁺ ion concentration in solution. The mean and standard deviation were calculated for concentration and pH (Fig. 2). The mean change in Ca²⁺ is x̄ = –59 ± 13.8 mg/L. On the other hand, the mean pH change is x̄ = –3.83 ± 0.29. Further statistical analysis to confirm significance was performed using a paired t-test (95 % confidence). The results indicate a p-value less than 0.05, confirming that the changes in both Ca²⁺ concentration and pH after treatment are statistically significant.

DI water (0 mg/L Ca²⁺, pH ≈ 6-7) showed no change after treatment (Fig. 3). The lack of H⁺ ion increase indicates that the resin did not release H⁺ ions into DI water, as there were no Ca²⁺ ions to exchange. This contrasts with tap water results, because the Ca²⁺ ions in tap water were exchanged for H⁺ ions from the resin, leading to a pH drop. Thus, this methodology effectively demonstrates the Ca²⁺ ion removal is inherently due to the ion-exchange mechanism of the EWS resin.

In summary, we have demonstrated that the EWS resin is particularly effective at removing Ca²⁺ ions from hard tap water (by removing 59 ± 13.8 mg/L), as evidenced by a statistically significant drop in ion concentration after treatment. The measurement of the pH further supports the ion-exchange mechanism, where Ca²⁺ ions are replaced by H⁺ ions from the resin. Furthermore, distilled water showed no significant change in pH due to the absence of Ca²⁺ ions to exchange, validating our experimental approach. It may be important to note the potential limit in detection (LOD) of the Ca²⁺ ion-selective electrode, which may affect the accuracy of very low concentration measurements post-treatment.

In the experimental setup produced by this report, the ion-exchange of EWS resin resulted in 98.8–100 % Ca²⁺ removal. Comparatively, Cetin (2014) yielded similar Ca²⁺ removal, at ~100 % [2]. In summary, the EWS resin performs nearly as well the resin used in Cetin's water-softening trials, and its high removal rate indicates it is still a viable product to use for industry.

[1] EDRO Corporation, “Water Hardness,” EDRO Corporation News, Sep. 25, 2025. [Online]. Available: https://edrocorp.com/141104news.html

[2] G. Cetin, “Removal of hardness of earth alkaline metals from aqueous solutions by ion exchange method,” ISRN Analytical Chemistry, vol. 2014, Art. ID 146046, PDF pp. 4-6, 2014. [Online]. Available: https://doi.org/10.1155/2014/146046