Chlorine in Water

Introduction

The amount of chlorine in a water sample will be found by using the TesTab^® color comparison method.

Concepts

• Chlorine levels
• Parts per million
• Water testing

Background

Chlorine is a greenish-yellow, corrosive gas that produces a suffocating odor. It is not naturally found in water at any appreciable levels. Chlorine is added to municipal water treatment plants and to swimming pools where it acts as a bactericide. Chlorine reacts with water to form hypochlorus acid, HCLO. The hypochlorus acid kills microorganisms in the water and eventually breaks down to form chloride ions, Cl^–. Swimming pools should have a chlorine level greater than 1 ppm. Chlorine in drinking water supplies is generally maintained under 0.75 parts per million. Large levels of chlorine introduced to streams, lakes, rivers, and ponds can be harmful and possibly fatal to aquatic organisms.

Materials

Safety Precautions

Chlorine DPD #4R TesTabs^® contain chemicals that may irritate skin or be harmful if swallowed. The TesTab reagents used in this kit were designed with safety in mind. The single-use, foil-packaged TesTabs are easy to dispense. Store TesTabs in a cool, dry place and only open when ready to use the tablet. A single tablet, either alone or reacted with a sample, is a low health hazard; however, TesTabs should not be ingested. Wear chemical splash goggles and chemical-resistant gloves. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. In the field, reacted samples may be poured into a container for later treatment. Dispose of reacted samples down the drain with plenty of water according to Flinn Suggested Disposal Method #26b.

Procedure

1. Fill the water sample tube to the 5-mL line with a water sample.
2. Add one Chlorine DPD #4R TesTab^® to the tube.
3. Cap the tube and mix the solution until the tablet has dissolved.
4. Compare the color of the sample to the chlorine color comparison chart.
5. Dispose of the reacted sample according to the instructor and rinse the water sample tube twice with the water sample for the next test.

Teacher Tips

• Enough materials are provided for 15 tests.
• It’s a good idea to collect several water samples from each site that is tested. It is also wise to test the samples within one hour of collection if possible.
• Chlorine DPD #4R TesTabs^® contain diethyl-p-phenylenediamine (DPD). When chlorine oxidizes DPD, a pink color is formed in proportion to the chlorine concentration.
• The range of the chlorine DPD TesTab is between 0 and 5 ppm.
• TesTabs are a vendor product of the LaMotte Company. SDSs are available through the manufacturer website.