How stuff works: chlorine bleach

Chlorine bleach is one of those things that you probably have around the house because it is incredibly versatile. It is great for making whites whiter in the washing machine. It is a good disinfectant, killing germs on counters and bathtubs. It will remove stains on tile and outdoor furniture. And it is pretty safe, relatively speaking — so safe that people drink it every day in their tap water and swim in it in swimming pools.

Let's take a look at how chlorine bleach works.

When you buy a bottle of chlorine bleach at the store, what you are buying is sodium hypochlorite mixed with water. Sodium hypochlorite is NaOCl. Since table salt is NaCl, bleach is very similar to table salt and reverts to table salt if left out.

For example, the bleach in tap water will be gone if you let an open container of water stand for 24 hours. This is especially important if you have fish in an aquarium. Fresh tap water will kill fish because of the chlorine. But if you let the water stand for 24 hours, it is fine for fish.

How does bleach remove stains?

Many natural stains from things like grass (green), carrots (orange), mildew (brown) and tomatoes (red) are caused by chemicals called chromophores.

A chromophore molecule creates a color by absorbing some colors of white light and reflecting others. If you can change the shape of a chromophore or break it apart, it becomes colorless. The oxygen in a bleach molecule is able to attack chromophores and break them up. Of course it will attack other molecules in the fabric as well, so frequently-bleached fabrics (especially cotton) tend to break down faster if washed repeatedly with bleach.

How does bleach kill bacteria to disinfect surfaces? It works in something of the same way that heat does to kill germs. Inside a bacteria cell are thousands of protein molecules that are intricately folded. These proteins are essential to a bacteria's life. Bleach causes these proteins to unfold or to clump together. This clumping is the same kind of thing that happens when you heat an egg — the protein molecules in the egg solidify as they clump together.

If you put bleach in water, it will kill bacteria and tend to lessen anything that might be coloring the water. That's why chlorinated water is so common in municipal water systems and swimming pools. Tap water might have a chlorine concentration of 1 part per million (anywhere from 0.2 ppm to 4 ppm is legal). A swimming pool can go as high as 4 parts per million for swimming, and can go much higher for shock treatments.

If you are stuck in an emergency situation or you are out hiking, you can purify water yourself with chlorine bleach. You can add 8 drops of bleach per gallon of water, or 2 drops per liter of water, cap it, shake it and let it sit an hour. It won't kill some parasites, but it will kill most everything else in the water.

However, strong chlorine bleach (like you find in a bottle of bleach, which is 5 percent to 6 percent sodium hypochlorite mixed with water) is not something to treat lightly. You do not want it getting on your skin, in your eyes or into your lungs. If you dilute one ounce of bleach with 8 ounces of water you have a solution that kills germs but is not nearly so dangerous to your eyes and skin. But still, treat it with respect.

Work with bleach in a well ventilated area. If you are using it in a bathroom, turn on the fan or open a window. If you get chlorine bleach on your skin, wash it off immediately using plenty of water. If you do not, you can get chemical burns from undiluted bleach that are not pleasant at all. Use gloves to keep bleach off your hands. Use goggles to keep bleach out of your eyes. Be very careful when pouring bleach out of a bottle. Also avoid mixing bleach with any other chemicals, especially ammonia. It produces toxic vapors.

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