 Okay. So the last topic of this chapter is water. This is actually the most important one. So what do we all know the molecular formula is H2O and oxygen is sp3 hybridized here where the two lone pairs are there in the sp3 hybrid orbital and the two hydrogen present like this. Okay. So we all know hybridization is sp3 geometry is tetrahedral. And what is the shape here shape is V shape or bent shape or angular shape be bent or angular. Okay. So all these orbitals are sp3 hybridized orbital in which the lone pairs present and the bond pairs also there. Okay. Bonding and all we know we have discussed it already. So its property is like first of all pure water right down your H2O is bad conductor of electricity conductor of electricity colorless test less and order less due to hydrogen bonding due to H bonding. It is also known as it is also known as associated molecule associated molecule. Next I don't pure water is neutral is neutral and act as as weak electrolyte. What is electrolyte, what is electrolyte electrolytes are those substance or molecules, which dissociates into ions in aqua solution. For example, if you take a NACL right so NACL when you dissolve in water. It doesn't exist as a molecule that is NACL, but it exists as any plus and CL minus. So this is called an electrolyte which dissociates into its ionic form. H2SO4 is an electrolyte. HCL is an electrolyte. Basically all assets base and salts are electrolytes. All assets base salts are electrolytes correct. Now electrolyte also depending upon its dissociating tendency to what extent it can dissociate. It is classified into two categories, weak electrolyte and strong electrolyte. No, it's not it dissociates but dissociation is not 100%. Means to some extent it will dissociate it exists at H plus and OH minus, but not completely. Okay, because it is a weak electrolyte weak electrolytes are those substance which does not dissociate completely means suppose you have taken 10 molar. I'm trying to make suppose we have CS3 COOH it is also a weak electrolyte. Okay, so it dissociates as CS3CO O minus and H plus. If you have suppose, suppose initial concentration is C, this is zero, this is zero. So after some time, it won't become zero and this is C and C it won't happen. Means this compound will entirely it won't convert into its ions. Some amount of this will be left in the solution means out of C suppose few moles will get dissociate. Suppose X most dissociate out of C. So it will be C minus X, X and X like this will happen. But if it is a strong electrolyte for example, if I'm taking NACL NACL is a strong electrolyte. So it completely dissociates into any plus and C minus. So if it is C zero zero initially. So after some time this becomes zero there's no more NACL present entirely it converts into any plus and C minus. This is the difference between a strong and weak electrolyte. Yeah, got it. So all know there will be exchange of electron, but the molecule will retain its property in the solution. There will be in after some time if you look at this mixture in the mixture you will get CS3 COH you'll get CS3 CO minus you'll get H plus so there will be transfer of electron, but entirely this compound won't decompose into this. That is what I'm talking about. Okay. So is this about electrolyte we'll discuss in I mean equilibrium. Okay, we will talk about the strong and weak electrolyte. Usually you can understand all the strong acids strong base and salt of strong acids and strong base are strong electrolytes. Okay, what did I say in order in general you can and can memorize this strong acids, strong base, and salt of strong acid and strong base. Okay, all are strong electrolytes, weak acid, weak base and salt of it are weak electrolyte. Yeah. This is the understanding of electrolyte we have now water we have two types. Okay, right down. There are two types of water. That is hard water and soft water. This is the most important topic of this chapter. The only thing that you need to keep in mind for sure. First of all, you write down the definition of soft water. Write down water which produces water which produces sufficient leather with soap is called soft water. Hard water, it's not like hard water does not produce, but relatively hard water consumes more amount of detergent or soap to produce leather. Okay. So, write down. It forms, it forms insoluble is come before. It forms leather with soap means there are some particles present into hard water. Those particles consumes soap first. Okay, and forms is come insoluble is come. Once all these particles precipitated out, then it starts producing leather with soap. So basically hard water contains some particles, okay, some ions, which consumes the soap and does not produce leather. Okay. Once all these particles, you know, get gets precipitated, then it starts producing leather. Okay. So the difference between the two types of water is, is that soft water contains relatively lesser amount of, you know, consumes relatively lesser amount of soap or detergent to produce leather, right? Hard water consumes more amount of soap or detergent, correct? In like daily use, the water that we use is hard water. Okay, depends upon areas like, like what amount it requires of soap and detergent, but usually it is hard water. Now, what you need to know that what is the reason of hardness first of all, right? What are the different types of hardness and what is the removal, you know, what is the way by which we can remove these hardness, okay? So, you see, there are two types of hardness, right? And before that, you write down the reason of hardness and then we'll see the types of hardness here. The reason of hardness you write down, it is because of, it is because of the presence of, presence of bicarbonates and sulphates and sulphates of calcium and magnesium of Ca2 plus iron and Mg2 plus iron. In general, this is the thing we have, bicarbonates and sulphates. So once all these ions precipitates Ca2 plus and Mg2 plus, then it starts producing that. Okay, so there are two types of hardness we have, types of hardness. First one is temporary and the second one is permanent hardness, permanent hardness. Next you'll see what is the reason of this temporary hardness and what is the removal way. First write down, first write down temporary hardness. It is due to, is due to the presence of, presence of bicarbonates of calcium and magnesium, bicarbonates of calcium and magnesium, okay? What is the removal process? Removal process. The first, the simplest method is by boiling. You can simply boil and this kind of hardness will go off, okay? So what happens on boiling? On boiling, bicarbonates decomposes into, decomposes into carbonates, which precipitates out. So if you look at the reaction here, bicarbonates we have CaH CO3 whole twice. You heat this, it forms CaCO3 carbonate, CO2 and H2. This forms the PPT and will precipitate out, right? Similarly, we have MgHCO3 whole twice. And when you heat this, again it forms MgHCO3 PPT plus CO2 plus H2. Done. Now the second method of removal we have here is by Clark's process. In Clark's process, one question they ask very often here that what we add in Clark's process in water, right? For the removal of temporary hardness. So this process involves right down, this process involves the addition of slag lime, calculated amount of slag lime. What is the formula of slag lime? Slag lime is calcium hydroxide CaOH whole twice, okay? CaOH whole twice, slag lime. So we add slag lime into this, which forms insoluble carbonate here. So if you look at the reaction again, we have bicarbonate CaHCO3 whole twice. And when you add CaOH whole twice in this, it converts into two molecules of CaCO3 and H2O, again this carbonate forms the PPT and precipitate out. If you talk about the next one is MgHCO3 whole twice. It reacts with CaOH whole twice, converts into two CaCO3 plus H2O, right? This is the reaction. Now in this, instead of slag lime, this is important, note down this point. Instead of slag lime, we can also add, we can also add CaOH quick lime for this purpose. Means in class process, the answer is CaOH whole twice and this is what we add. But we can also have the same purpose, same effect when we add CaO. Why? Because this CaO, if you add into water, so this reacts with H2O and converts into slag lime, which is CaOH whole twice. And then this slag lime will react with the bicarbonate which is present in the water. And gives the same reaction. So we can also have the same thing when we add CaOH quick lime into it. Next write down the second one, that is permanent hardness, permanent hardness. It is due to the presence of, the reason write down, the reason is the presence of sulphates and chlorides of, chlorides of calcium and magnesium. Write down, to remove this type of hardness, to remove this type of hardness. Yeah, one second, I'll go back. Yeah. So presence of sulphates and chlorides of calcium and magnesium. Write down in this, to remove this type of hardness, to remove this type of hardness. We use, we use various substance or molecules. To use this type of, you know, how to remove this type of hardness, we use various substance. And these substance are called water softeners. These substance are called water softeners. Right. And the various water softeners are various water softeners. And this one is, water softeners are, the first one you write down, we have washing soda. What is the formula of washing soda? Its chemical name is sodium carbonate, Na2CO3. Write down, it removes both temporary and permanent hardness. All these informations are very important. Both temporary and permanent, temporary and permanent hardness. So what happens in this? The chloride we have CaCl2. Chloride, once you add washing soda, that is Na2CO3 into this. And we heat this. First of all, it forms calcium carbonate precipitates out and it forms NaCl. Right. If you have CaSO4, sulphate, Na2CO3, it converts into, again CaCO3, plus Na2SO. Okay. This is for permanent hardness. Chloride and sulphate. Okay. For permanent hardness. For temporary hardness, if you look at the reaction here, it is because of bicarbonate. So reaction of bicarbonate, CaHCO3, whole twice plus Na2CO3. It forms, again CaCO3, plus NaHCO3. Right. This is how it removes the temporary hardness as well. Okay. Instead of Na2CO3, we can also use, instead of Na2CO3, we can also use NaOH, we can also use NaOH or we can also use sodium phosphate, Na2, Na3PO4. These two also we can use instead of Na2CO3 for the same purpose. NaOH and Na3PO4 will get this. So washing soda is one of the water softeners. NaOH also water softeners. Na3PO4 also water softeners. Yeah, you can use. Both will give you the same thing. Both we can use. CaOH whole twice we can use washing soda. We can use the same thing. Another water softener we have, we call it as permuted. Common name is permuted. Okay. This technical name is hydrated silicates of. It is the hydrated silicates of aluminium and sodium. Minium and sodium. Okay. Hydrated silicates of aluminium and sodium. The formula is Na3, Na2, Al2, Si2, O8. And it's a hydrated form. So water of distillation we can have. XH2. The chemical name is sodium alumino silicate. Or we also call it as sodium geolite. Sodium geolite. This is also used for the removal of both temporary and permanent hardness. Right down here. It removes both temporary and permanent hardness. Okay. Then the third and the last one we have, the water softener. We call it as calgan. It is the complex salt of, complex salt of metaphosphoric acid. Metaphosphoric acid. Also call it as sodium hexametaphosphate. Sodium hexametaphosphate. The formula if you see, this NaPO3, 6. The actual bonding if you see, it is a complex compound. And the actual bonding is Na2, open bracket. Na4PO3, 6, back close. This is the actual bonding. It easily eliminates calcium and magnesium ion. I'll show you the reaction here. 2CASO4, sulfate of calcium. Reacts with this Na2, Na4PO3O6. It converts into Na2, Ca2PO3, 6. Plus we get 2 Na2SO4, sulfate. It removes. If you have MGSO4, Na2, Na4PO3, 6 converts into Na2MG2PO3, 6 plus 2 Na2SO4. This is the reaction we get. Okay. This is how it removes both type of like this one. The calgan removes only permanent hardness item. It removes only permanent hardness. Done. Finished, guys. Yeah. So this is it for this chapter. Okay. We're done with this. Next chapter, we will be starting S-Block. That is group one. Okay. So we don't have time much today. So I'm not starting this new chapter today. We'll start it next class. We'll see some questions. Okay. Questions on this state of matter. Show you some question. Okay. Try this question. 40 to 44. All question is solved and then we'll start discussing it. Five questions. 15 minutes.