If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Bleaching powder

Let's see how bleaching powder is made and where it's used. Created by Ram Prakash.

Want to join the conversation?

Video transcript

- [Ram] In this video we are going to talk about bleaching powder and you might be using this at home. We will see how this is chemically made and what are it uses. So lets begin so bleaching power this is chemically known as calcium oxychloride and this is found when chlorine is passed toward chlorine gas is passed toward dry slaked lime. Okay so lets lie down the chemical reaction. So chlorine gas is Cl2 and when this is passed through a dry slaked lime remember what is the chemical formula of slaked lime. Well let me help you recall this. So in chemistry whenever we say lime we do not mean lemon but we mean calcium oxide. Also known as quick lime and this is called quick because it quickly combines with water with water they will be combination reaction and finally we will get calcium hydroxide or red lime and this is called a slaked lime. So basically we are drying this out to remove excess water so the chemical formula is going to be same Calcium hydroxide. Let me write with same color. CaOh twice and these both are going to react and finally we'll get calcium oxychloride CaOCl2 and with this we also get water plus H2O. So this is how you form bleaching powder. You pass chlorine gas through dry slaked lime and you get calcium oxychloride or bleaching powder. Oh by the way the actual formula bleaching powder is slightly more complex to understand that we'll have to study many more concepts okay. So we will do that in future videos but for now just understand that bleaching powder is calcium oxychloride and its formula is CaOCl2. Okay with this I would like to review one more thing. See this is bleaching powder is one of the compounds that is found with the help of sodium chloride NaCl. The common salt that we use in our kitchens. Yes see to make this we require chlorine gas right? And you would remember that chlorine is one of the products the byproducts that gets formed when we do electrolysis of NaCl aqua solution of Nacl. When we pass electricity through a solution of water and NaCl chlorine gas is also getting involved and this chlorine gas could be used to make bleaching powder that's what makes NaCl so great and important. Because is can be used to make many other chemical products. So now with this lets go ahead and see what are the uses of bleaching powder. So the first is it is used as oxidising agent in chemical industries. See bleaching powder is a very good oxidising agent. Now what do I mean by that? So you would recall that oxidation is oxygens addition meaning if oxygen is getting added to any element or compound. That means that they are going under oxidation. For example carbon plus oxygen this gives us carbon dioxide. So here oxygen was getting added to carbon that means carbon is going under oxidation. It is getting oxidised and we are getting a new compound altogether. So bleaching powder is a very good oxidising agent this means that this can easily oxidize other compounds and elements. It can easily add oxygen to other compounds and elements. And so whenever this is a requirement it would require to add oxygen to something in chemical industries we use bleaching powder as oxidising agent. Now another uses is to decolor or bleach certain materials. For example if you want to decolor cotton or linen in textile industries. See my favorite T-shirt is black in color but it is made up of cotton cotton material and cotton is not naturally black in color. So how did this color happen to come over here? So I guess the makers of the T-shirt they would have put the cotton T-shirt into a black color dye and the molecules of the dye they would have got stuck on this T-shirt and that's how my T-shirt appears black in color. So now when I put this in bleaching powder the molecules of the bleaching powder they will oxidize the black color molecules of the dye and then chemical reaction happens and a new compound gets formed and this has lost it's black color and that's how my T-shirt it looses it's black color it has become faded. So that how you can use bleaching powder in texting industries to bleach cotton and linen you can also use it to bleach your jeans and give it nice shaded look but be very careful while trying this at home. Okay we also use bleaching powder to decolorize wood pulp in the paper industry. See the paper that we use is very white in color but it is made from wood pulp which is not very white in color right? So to decolorize this wood pulp we use bleaching powder and similarly we also use it to bleach or remove stain from clothes. See whenever there is some stain or some color mark on your clothes that's very strong color right? And to remove the color or to decolorize it we can use bleaching powder for the same thing. One more use case of bleaching powder is for disinfecting water. See water can have many microorganism in it that can be very harmful for the human body. So when we mix bleaching powder and water it gives off chlorine and chlorine is toxic for the microorganisms it even kills them. So that's why drinking water is first treated with bleaching powder before supplying it to our houses and for the same reason we also treat our swimming pool with bleaching powder and that's why it smells of chlorine afterwards. Now lets summarize the video. In this video we talked a lot about bleaching powder. We saw what is it's chemical formula we saw how to prepare it and we also saw that it has two properties. One that it can oxidize and the other that it is toxic and based on these properties it has got some uses based on oxidizing capacity it is being used in chemical industries, paper industries, and textile industries. I hope you remembered how and based on it's toxic property it is used to treat water. Now I hope you recall all of these things and if you don't you can go back and watch the video again.