8.31.2010

bp's science: how does bleach work? (v.1)

So how does chlorine bleach get out nasty stains? Hmm, well we've got to do a bit of chemistry to explain it. Well we don't have to, but how long has it been since you've dabbled in chemical equations? That's what I thought.

Chlorine gas is made easily from table salt. You heard me, table salt. Table salt is sodium chloride (NaCl) and when it reacts with water (H2O), it creates chlorine gas (Cl2). Now if you put salt in water and stirred it, this reaction would not occur. If it did, none of us would be swimming in the ocean. You need electric energy for the following reaction to happen:

2NaCl + H2O arrow Cl2 + H2 + 2NaOH

To make bleach, the stuff you buy and the compound in bold letters, you must use the stuff you made above and:

NaOH + Cl2 arrow NaOCl + HCl

Now, once you pour that stuff in your washer or put it on a cloth and scrub your striped shirt with it to get out ink (thereby ruining your shirt - we've had that happen in our household) the chlorine is reacting to create atomic oxygen.

NaOCl + H2O arrow HCl + NaOH + O

**By the way, cheers to those of you who have had the patience and made it this far.**

Apparently, atomic oxygen is highly corrosive and it changes the molecular structure of a chromophore, the chemical compound that creates color. When the molecular structure is changed, the chromophore no longer reflects color. Good bye stain.

see here and here for a discussion on bleach, and blame me for the final reaction...

3 comments:

kel said...

it's good to have you back. looking forward to pics, etc. from UT.

thanks for the chem lesson. this is when chemistry is still interesting and makes sense to me.

so here's a question: why does hair spray take out ballpoint pen ink?

jo said...

I had no idea that it was oxygen (atomic or otherwise) that did the trick. You learn something every day on BP's Science Tuesday. Go redox reactions!

ash said...

kel, I will work on the hairspray question. I am curious too.

jo, I am impressed that you pulled "redox" out of your chemistry hat.

Thanks for reading guys.