Water purification is a major issue throughout the world; this lesson teaches students how they can easily chlorinate large volumes of water to kill the bacteria using some electricity and basic chemistry. This lesson is likely part of a water purification module, and the completed lesson should involve some form of water filtration and testing. Please note that chlorination only kills bacteria and viruses; it does not filter the water in any way, so one is still in danger of drinking dead organisms, dirt, and heavy metals.

As part of a larger water purification module, perhaps one student group could make a chlorinator, one group could use sunlight, one group could boil water, etc– and then everyone performs the same tests to measure the success of their methods.

If this lesson interests you, there's lots to do:

• Write the teacher's guide
• Adapt the default evaluation form
• Design and upload illustrations

If you're interested in doing any of that, great! Leave a note on the lesson index that you're taking charge.

Whether or not you're interested in writing a part of this lesson, please leave lots of comments on this page, the teacher's guide, and the evaluation form. Thanks!

- how to electrolyze salt water

- the principle of electrodes

- applying voltage to an electrode (difficulty varies depending on the situation!)

none

none

Students take apart a D-cell battery, then use the salvaged graphite electrodes to electrolyze salt water and make chlorine.

PEN lessons that meet the requirement are noted in brackets.

basic knowledge of electricity [battery]

can safely use a sharp knife to cut battery casing, can deal with semi-hazardous chemicals and potentially high voltage

Water filtration, UV water treatment

none

none

none

- 2 cheap, old D-cell batteries with graphite cores

- sharp knife

- gloves for dissembling batteries

- small container for water

- clean-ish water

- salt

- power source that can give ~5V to the electrodes

- cables and some way to attach them to electrodes

None

newspaper or plastic bag on which to take apart battery, so the powdered manganese oxide doesn't get everywhere

This can be more of a demonstration or small-group exercise than an actual lesson. It may be difficult for more than 5 students to make a chlorinator at one time, and it doesn't involve enough interesting engineering to deserve an entire lesson. Supervision may be important, too.

Why should students want to participate in this lesson?

- see what happens when you send a current through salt water

- take apart a battery and learn about electrodes

- make a useful chemical

Why should teachers want to teach it?

- water purification is important

- teach students about electrolysis

If this lesson (and its prerequisites) were the only PEN lessons someone took, what should they be able to do?

Take apart a battery and use the electrode to electrolyze salt water and produce chlorine.

If you had to teach this lesson tomorrow morning, what would you spend tonight working on? (assuming that materials were not an issue)

Ensure lab safety– the battery is toxic, and electrodes could be dangerous if students aren't careful.

If you hadn’t taught this lesson before, what questions would you have for someone who had taught a very similar lesson?

How can you test for chlorine (ie titration)? Would this be a good thing to include in the lesson? How effective is this for water purification?

If the only materials available were broken radios, TVs, and computers, could you do all the electronics in this lesson? (assuming you had solder, soldering irons, etc.) If not, what would be missing?

Yes, if there were 2 D-cell batteries.

If the only structural materials available were dish-cloths, cardboard, and plastic bags, could you make the mechanical bits of this lesson? (assume equipment as above) If not, what would be missing?

Yes, if you can hold the electrodes apart in water in a plastic bag. Something more solid would be better.