Overview
This workshop introduces students to electrolyzed saline to produce a very dilute hypochlorous acid (HOCl) solution, roughly 0.01% strength. HOCl is a weak acid with disinfection properties and is often used for sanitizing surfaces. The activity is designed for safe, supervised learning and emphasizes chemical concepts, safety, and measurement accuracy aligned with ACARA v9 standards.
Learning goals
- Understand electrolytic cells and the basic chemistry of HOCl formation.
- Learn about molarity, dilution, and concentration calculations.
- Discuss safety considerations when handling electrolytes and produced solutions.
- Connect the experiment to real-world disinfection practices and hygiene.
Materials (per group)
- Sodium chloride (table salt), ~5 g
- distilled water, ~500 mL
- Electrolysis power supply (DC, adjustable, safety-rated)
- Two inert electrodes (platinum or graphite work well; avoid reactive metals)
- Beaker or small plastic container (600–1000 mL)
- pH test strips or a pH meter
- Measuring cylinders or graduated cylinders
- Personal protective equipment: safety goggles, gloves
- Motorized stirrer or glass rod for mixing
Safety considerations
- Conduct this activity under direct adult supervision. Do not ingest the solutions.
- Wear eye protection and gloves; handle electrical equipment with dry hands and away from liquids outside the setup.
- Avoid mixing with strong acids or bases; do not introduce metal contaminants into the electrolyte.
- Dispose of solutions according to local regulations; never pour leftover electrolytes down the drain untreated.
What you’ll do
- Prepare the saline solution: Dissolve 5 g of NaCl in about 500 mL of distilled water in the beaker. Stir until fully dissolved.
- Set up the electrolysis: Place the two electrodes into the saline solution, making sure they do not touch. Connect the electrodes to the DC power supply. Use a low current to start (for example, 0.5–1 A) and gradually adjust as needed while monitoring the setup.
- Electrolyze: Turn on the power supply and run the electrolysis for a controlled period (e.g., 5–10 minutes). Observe any gas production at the electrodes and note changes in the solution.
- Test and dilute to ~0.01% HOCl: After electrolysis, measure the volume of solution. To estimate concentration, you can perform a simple dilution calculation: if you produce a small amount of HOCl in the solution, you can dilute to a final volume and estimate molarity. Note: HOCl testing kits or pH indicators can help infer acidity/disinfection potential, but exact HOCl concentration requires specialized reagents; discuss theoretical calculation and practical approximations with your teacher.
- Safety check and analysis: Measure the pH of the final solution. A mildly acidic solution is expected. Discuss how HOCl behaves in water and how concentration affects disinfectant properties.
Discussion questions
- What is the role of the chloride ions in forming HOCl during electrolysis?
- Why is the electrolyte solution not simply water and salt? How do electrode materials influence the reaction?
- How would changing the current or electrode material affect the amount and quality of HOCl produced?
- What safety and ethics considerations come with producing sanitizing agents at home?
Connection to ACARA v9
This activity aligns with Year 9–10 chemistry strands focusing on chemical reactions, redox processes, and practical laboratory skills. It emphasizes inquiry, measurement, and safety while applying chemistry to real-world sanitization concepts.
Extensions
- Investigate how varying salt concentration affects current and gas production (Faraday’s laws conceptually).
- Compare HOCl effectiveness against common microbes using safe, classroom-appropriate simulations or literature reviews.
- Explore alternative electrolytes and electrode materials and discuss why some materials are preferred for durable, safe electrolysis.