 Okay, so last thing we have to discuss here, correct, correct, last thing we have to discuss here is Henry's law, write down, Henry's law, Henry's law, so write down at a given temperature, at a given temperature, the amount of a, the amount of a given gas, given gas dissolve per unit volume, per unit volume of a given solvent, of a given solvent and this solvent is liquid here, given solvent is directly proportional, is directly proportional, is directly proportional to the partial pressure, to the partial pressure of the gas in equilibrium with the liquid, in equilibrium with the liquid, so Henry's law, it is actually applicable for the solution of liquid and gas, where gas is the solute which is B and liquid is a solvent which is A, Rawls law if you remember, Rawls law if you remember, it is valid for liquid in liquid solution not liquid in gas, okay, so this is one thing you must keep in mind, right, so Henry's law is valid for liquid in gas and Rawls law is valid for liquid-liquid solution, okay, this is the one difference we have, now what it says that in a given like amount of liquid, in a given amount of liquid the amount of gas dissolved in this liquid depends upon the partial pressure of the gas, suppose these are the gas we have present in the air, so gas which has more partial pressure will dissolve more into this liquid, okay, according to the partial pressure of the gas, right, so the amount of gas increases into the solution if the partial pressure of the gas increases, copy down this, okay, so what we can write here, the amount of gas dissolved or the concentration of gas if I am taking as A, the concentration of gas in the water, this concentration of gas in the water is A suppose, so A is directly proportional to the partial pressure of the gas, of the gas, so A is directly proportional to the partial pressure P of the gas, if I remove this proportionality sign, A is equals to k H into P where this k H is the Henry's laws constant, k H is the Henry's constant, Henry's constant, this k H, the factor on which the k H depends upon, k H depends upon you write down, depends on, the first factor is the solvent used, solvent used, in this, this is not that much important but what you have to keep in mind for a given gas, for a given gas the value of k H, the value of k H is different if solvent is different, if solvent is different, so for different solvent for the same gas we may have different value of k H, Henry's constant, second point, pressure as the pressure increases, pressure increases, dissolution increases, dissolution increases, more pressure, more will be the dissolution, for this you can keep the example in mind that in cold ring the gas that is dissolved, CO2, that is dissolved at very high pressure, we used to, like the packaging of cold ring is done is very high pressure, so that the gases must be dissolved into the cold ring sample, understood, so high pressure is required for the dissolution of gas, third point, these two second, third point is very important point we have which is temperature, so as temperature increases, as temperature increases the value of k H also increases Henry's constant and when k H increases the solubility, solubility decreases, you see here for a given temperature if this k H decrease to make the product constant and when pressure decreases amount of gas dissolved in solvent also decreases, basically this you let it be, just one thing you keep in mind for, you must have, you must have drunk the boiled water, a warm water, warm water, so in warm water what happens, there's no taste, it looks like very, it tastes like very weird of the warm water, why this happens because at higher temperature when you boil the water, then all the gases which is dissolved into the water that escapes into the atmosphere and there is no dissolved gases into the water, that's why the taste changes, even one example I have given you in the class that all these aquatic animals used to live deeper into the sea, not at the surface of like the surface of the water, just below the surface of the water, because there the temperature is higher comparatively because of the sunlight, so that's why the oxygen content in the water which is there on the surface is very less in comparison to the oxygen content which is there in the deeper in the sea, that's why most of the aquatic animal, they don't used to live at the upper surface of the water, they used to live deeper into the sea, because oxygen content is more over there, so the point here is what for dissolution of gas the favorable condition is what, high pressure, high pressure and low temperature, high pressure and low temperature is the favorable condition for the dissolution of gas, this you must remember, got it understood, high pressure and low temperature you have to keep in mind, k h and p as pressure increases k h decreases generally, and this constant decreases, so high pressure and low temperature you have to keep in mind, another thing you see if I ask you here what is the unit of k h, unit of k h is what, can you tell me, what is the unit of k h tell me, gram per atmospheric, how it is gram, a is concentration, no, a is concentration, so it is, so it is mole per liter per atm, this is a unit, it's not gram, it's mole per liter per atm, okay, now you see if I write down this k h on the right hand side, I can also write down this k h on the left hand side, right, so this is, if I write down this k h this side or we can also write this p in the other way, p is equals to k h dash into a and where this k h dash the another hand is constant is equals to 1 by k h we can write and its unit will be what, this unit will be liter atm per mole, this is another unit and this is another expression also, okay, this is the another unit, similarly you see if the number of moles of gases increases in the solution, so we can also say that the partial pressure of the gas is directly proportional to the mole fraction of the gas in the solution, more number of moles and hence more will be the mole fraction, hence we can also write p is equals to k h into x, again the another hand is constant, k h double dash or k h you can write, where the unit of this k h is what, unit of this k h is atmospheric, here, now the point is I have given you three different expression, right, for Henry's law, the first one the second one is k h dash into and the third one is k h into x in terms of mole fraction, got it, so which expression we are going to use in the question that the first thing, so to do this what you need to do here, just a second, okay, you need to find out the unit of k h, unit of Henry's constant, according to the unit given, right, we will use the expression, suppose the unit is atm it is given in the question, we will use this expression, if the unit is this, we will use this expression and if the unit is mole per liter atm, we will use the first expression, so depending upon the unit of k h, we will use the expression of Henry's law, is it clear, understood all of you, so this is what you need to keep in mind, write down one question on this, the k h of the k h of N2, the Henry's constant for nitrogen it is given 10 to the power 5 atm, atmospheric and this is at 298 Kelvin, the mole fraction, write down the question, the mole fraction, just a second, the mole fraction of N2, of N2 which is given in the question 80% in air is 0.80, I have written here also, mole fraction is 0.80, calculate the number of moles, calculate the number of moles of N2 dissolved in, dissolved in 10 moles, 10 moles of H2O at 298 Kelvin, 5 atmospheric pressure, do this question all of you, the total pressure is given 5 atmospheric, number of moles of water is given, mole fraction of N2 is given in air, you need to find out, k h is given, you need to find out the mole fraction of number of moles of N2 dissolved, then anyone, what is the answer, are you trying, tell me, I am not getting any response, then anyone did you get the answer, tell me first, Sahana, what about you, okay see this, I will just do this, what we need to find out, we need to find out the number of moles, so if you get the mole fraction, okay, so if you find out the mole fraction and then we can find out the number of moles, but and we know the mole fraction you see the k h value is given and the unit of k h is what, the k h value is given which is given in terms of atmospheric, right, so obviously the formula that we have to use here for this question that is partial pressure is equals to k h into x, the mole fraction of this, okay, so what is this partial pressure, this is the partial pressure of nitrogen, right, and the mole fraction of nitrogen, okay, so partial pressure of nitrogen we do not know, it is not given in the question, right, but we can find out this partial mode, partial pressure of nitrogen, k h is given, so partial pressure of nitrogen is what, we can write down the mole fraction of nitrogen in vapor phase into the total pressure, so mole fraction of nitrogen in air is given, 0.80, so that will be 0.80 into 5, total pressure is atmospheric, so that will be 4, so partial pressure is 4, k h is 10 to the power minus, sorry, 10 to the power of 5 and mole fraction of N2, so mole fraction of N2 is what, 4 into 10 to the power minus 5, it is the mole fraction of N2, right, and this mole fraction what we can write, it is the number of moles of nitrogen divided by the total number of moles, number of moles of nitrogen plus number of moles of H2O, now you see the number of moles of nitrogen, mole fraction is 4 into 10 to the power minus 5, it means what, the number of moles of nitrogen is very less in comparison to the number of moles of water, which is 10 moles given in the question, so what we can do, we can neglect water, neglect nitrogen with respect to water, because this value is very less, right, hence number of moles of nitrogen is very less, and we can write this as N of N2 divided by N of H2O, here we have neglected N2, number of moles of N2 with respect to water, number of moles of water is given 10, so the number of moles of nitrogen is equals to 4 into 10 to the power minus 5 into 10, which is equals to 4 into 10 to the power minus 4 moles, this question was asked in JEE, answer is this only, 4 into 10 to the power minus 4 mole, understood all of you, got it, so you need to just keep in mind that partial pressure of, partial pressure of N2 you need to find out, total pressure we cannot use here, okay, and that will find out with the help of total pressure, okay, right.