 Hello students, let's have our first practice session of this series in which I have come up with a lot of numericals from mole concept. I hope by the end of this video a lot of concepts from mole concept will get much more clearer for you. So let's start with our first question which reads find weight of 3 gram atoms of sulphur. Now one note point here before we start with this particular numerical gram atoms or gram molecules. It is the same thing as moles. You can say that it is a different name for moles. So whenever you see gram atoms or gram molecules it is nothing but they have given the value of moles. So here in this question they have told 3 gram atoms of sulphur. So it means 3 moles of sulphur is given to us. And they are asking the weight. So again mole formula how is moles related to weight n is equal to weight upon Mw and Mw is the molecular weight of sulphur. So 3 is equal to weight upon molecular weight of sulphur is 32. Therefore weight will be equal to 32 into 3 that is our 96 grams. This will be the final answer. Coming on to the next question find the number of atoms present in 16 grams of O3. Now O3 what is the molecular weight of O3? 48 grams. So 48 grams of O3 contains Na molecules of O3 and we know that one molecule of O3 contains 3 Na atoms. One molecule of O3 will contain 3 atoms not 3 Na. One molecule of O3 will contain 3 atoms of oxygen. So 1 mole of O3 means Na molecules or 48 grams will contain how many atoms? 3 into Na atoms. 3 into Na atoms. Now so we know that 48 grams of O3 is containing 3 Na atoms. So 16 grams of O3 will contain how many 3 Na upon 48 into 16. So 16 3 is a 48 3 3 cancel. So 16 grams of O3 will contain Na atoms in total. Next question pause the video and try the questions on your own first then only check your answer with the solution that is provided here. Now what is the next question? Calculate the mass of sodium which contains same number of atoms as are present in 4 grams of calcium. Okay very nice. So first I will find out number of atoms present in 4 grams of calcium. So we know that in 40 grams of calcium that is the molecular weight of calcium how many atoms are there? Na atoms of calcium. So in 4 grams of calcium how many atoms should be present? Na upon 40 into 4. So total Na upon 10 atoms are present in how many grams of calcium? 4 grams of calcium. And in the question it is said that this many atoms is equivalent to how much mass of sodium? How much mass of sodium? So now let's consider the mass of sodium as W. W upon Mw is equal to Na upon Na where W here is our mass of sodium and the number of atoms also here is of sodium but it is the same as this one. So we can place that particular value here W upon 23 is equal to Na upon 10 divided by Na. So Na Na gets cancelled when you solve this particular thing what we will get? W is equal to 23 upon 10 is equal to 2.3 grams. So this many number of atoms will be present in how much weight of sodium? 2.3 grams of sodium. Fourth question find the number of H2O molecules present in 252 milligrams of oxalic acid dihydrate. So first and first thing we will be finding out the molecular weight of this oxalic acid dihydrate. So H2C2O4.2H2O what will be the mass of this? Two atoms of hydrogen so 2 plus carbon is 2 so 12 into 2 plus oxygen is 4 so 4 into 16 plus one molecule of water weight is 18 grams so there are two so 2 into 18. Calculate this how much it will be 126 grams. So 126 grams is the gram molecular weight of this oxalic acid dihydrate. Now just now we have seen how much of water is present total in 126 grams of oxalic acid dihydrate 36 grams. So we can say that 126 grams of oxalic acid dihydrate contains 36 grams of water. So we can say that one any molecules any molecules of oxalic acid dihydrate is containing two any molecules of water or in other words we can say one molecule of oxalic acid dihydrate contains two molecules of water. Try to understand this. So 252 milligrams will contain how much amount of water. So 252 milligram means 0.252 grams 0.252 grams will contain how much grams of water 126 gram contain 36 grams so 36 upon 126 into 0.252 that will be around how much it will be 0.072 grams. So in this much amount of gram of oxalic acid dihydrate how much amount of water is present this many grams 0.072 grams. Now in case of water we know that 18 grams of water is nA is equivalent to any molecules of water. So 0.072 grams will be equivalent to how many molecules because ultimately they are asking the number of H2O molecules that is present in this 252 milligrams. So this 0.072 grams will be equivalent to nA upon 18 into 0.072 that will give you an answer of 0.004 nA. This many number of molecules of water will be present in this much amount of oxalic acid dihydrate. So this is our final answer. Next question which among the following is the heaviest? Which among the following is the heaviest? That means you have to find out the corresponding mass of each one of them. One mole of O2 is equivalent to how much weight? One mole of O2 is equivalent to 32 grams. One molecule of SO3 means 64 U. Sulfur is 32. Oxygen is how much? 48. So 32 plus 48 not 64 weight and then 80 correct 80. So this will be I remember you have done mistake in finding the molecular weight itself. So sorry this will be 80 grams okay not grams U because they have told one molecule. If they have told one mole then 80 grams we will write. So one molecule of SO3 is 80 U. If I convert this into grams it will be 80 into 1.66 into 10 to the power minus 24 grams. So this is already very very less. So this will be straight away out of the competition right. And then third one is 100 amu of uranium. 100 amu means how many grams? 100 into 1.66 into 10 to the power minus 24 grams. Again this one is straight away out and then we have grams itself 44 grams of CO2. So which one will be the correct answer? Which one is the highest one? heaviest one? Definitely option 4. 44 grams is heavier than this 32 grams and these two were already out of the race. So answer will be option D. Now we will practice certain more concepts but before that one important thing is there that is fundamental particles. What are fundamental particles? So inside the atoms also we have certain fundamental particles okay. So those are called electrons, protons and neutrons. We will be studying about those fundamental particles in details in the next chapter but for now just know that what is the mass and charge of each of this fundamental particles. It will be necessary in calculation. So this is the electron mass 9.1 into 10 to the power minus 31. This masses are in kilograms and the charge in coulomb will be minus 1.6 into 10 to the power minus 19 coulomb. Proton mass will be 1.672 into 10 to the power minus 27 and neutrons mass will be 1.674 into 10 to the power minus 27. I already told in a previous lecture that the mass of proton and neutron is almost almost same. So you can see here how it is almost same. It is 1.672 for proton and for neutron it is 1.674. So the difference is about 0.002. So it is almost negligible and the charge for proton is plus 1.6 into 10 to the power minus 19 coulomb and for neutron the charge will be 0. Neutron is a neutral particle. So we have learnt this. How to incorporate it? How it will come as a numerical? Let's see. So the question I hope you have noted this down. These values are very important. You have to remember it as such. So please take a note of it. Next the question is the number of electrons present in 3.6 ml drop of water with the density of 1 gram per ml. So if the density is 1 gram per ml that means 1 ml will contain how many grams? 1 gram. So if it is 3.6 ml it will contain how many grams? 3.6 grams. Water they have told? H2O. Very good. 18 grams of water contains how many molecules? Any molecules of water. We already know this. Now I have to find out one molecule of H2O will contain how many electrons? So if I talk about hydrogen what will be our atomic mass? Atomic number. Atomic number is 1 and how many hydrogen are there in? H2O I already told you. This is A. This is Z. This is mass number and this is our atomic number. An atomic number gives us an idea about number of electrons. So for hydrogen it is 1. So in H2O there will be 2 electrons from hydrogen plus in case of oxygen it is 16, 8. So this is the atomic number. So number of electrons and oxygen will be 8. So 8 electrons total 1 molecule of H2O contains total of 10 electrons. So NA molecules, NA molecules that is around 18 grams will contain how many electrons? 10 into NA electrons. So 1 gram will contain how many? 10 into NA divided by 18. Now what is the question? 3.6 ml. 3.6 ml means just now we have written it here 3.6 grams. So 1 gram contain this many amount of electron. So 3.6 grams will contain how many electrons? 10 into NA divided by 18 into 3.6. Cancel this output 0.2. So it will be how many NA electrons? So in 3.6 grams of water or we can also say 3.6 ml drop of water how many electrons will be there? 2 moles electron, 2 moles of electron will be present in that particular 3.6 ml drop. So this is our final answer. So the answer will be option A. Moving on C here. Now calculate the mass of one mole of electrons. Now mass of one electron is how much? Just now we have seen in the chart mass of one electron is 9.1 into 10 to the power minus 31 kilograms. So mass of one mole electron that means they are asking mass of NA number of electrons that will be nothing but NA into 9.1 into 10 to the power minus 31 kilogram. So when you multiply this you will get as 5.4 into 10 to the power minus 7 kilogram. So please remember this value 5.4 into 10 to the power minus 7 kilogram. This is the mass of one mole of electrons. So like this you can find out the mass of one mole of protons one mole of neutrons as well. Coming on to the next question calculate the charge of one mole of electrons. Now one electron charge of one electron was how much? Minus 1.6 into 10 to the power minus 19 coulomb. So charge of one mole of electrons that means NA electrons charge of NA electrons will be NA into minus 1.6 into 10 to the power minus 19 coulomb. When we calculate this we will get the answer as minus 96500 coulomb. Now this particular value we will be seeing later in our 12th grade in the chapter electrochemistry. This particular 96500 is nothing but one faraday. Whenever we will talk about the charge of one mole of electron there because in electrochemistry we will be studying about the loss of electrons gain of electrons. So we will be seeing there if one mole of electron is involved anywhere we will say one farad of charge will be required or one farad of charge will be involved in that particular process. So this is known as one farad charge. So one mole electrons is equivalent to one faraday of charge that is equivalent to 96500 coulomb. This was question number A. Now question number B will be charge on, it's a magnesium plus 2 they're asking, charge on 1 mg plus 2 will be how much? 2 into 1.6 into 10 to the power minus 19 and this will be plus charge because 2 electrons have been lost means what? This plus 2 means 2 protons are extra. So this is the charge of 2 protons. So 2 into 1.6 into 10 to the power minus 19. So the charge on Na mg 2 plus will be 2 into 1.6 into 10 to the power minus 19 into Na and just now we have calculated this 1.6 here Na into 1.6 which came as 96500. So we can say 2 into 96500 that will be around. We can say we can call it as 2 farad. So whenever there is a particular ion for example AL plus 3 how much charge it is carrying? 3 faraday plus 3 faraday positive it will be okay. So like this we have to calculate the charge of electrons and protons. Now coming on to the next question at STP the density of a gas molecular weight is given as 45 in gram per litre is. Now here density formula is PM by RT. This regarding this particular formula we will be studying in details in the upcoming lecture but for now we can do it in a separate way also the general formula that we know already that is at STP we have studied that the volume of the gas will be 22.7 at STP the volume occupied by the gas will be 22.7 this is the volume and the mass is given mass is given as 45. So density will be nothing but mass upon volume that is 45 upon 22.7 that is nothing but 2. So the density of the gas in gram per litre will be 2. So the answer is option C but we could have calculated it in this particular formula putting the values in this particular formula as well. So we will be seeing about this formula in the upcoming lectures. Moving on question number 10 one mole of CH4 contains four gram atoms of hydrogen three gram atoms of now I told you what does gram atoms mean moles this also means moles. Okay now let's see one mole of CH4 what is the data we can decipher any molecules of CH4 it should contain. So definitely this will be wrong then one mole of CH4 contains any molecules of CH4 and one molecule of CH4 contains one atom of carbon plus four atoms of hydrogen. So one mole of CH4 will contain one mole of carbon and four moles of hydrogen. So definitely the answer should be option A because it should contain one mole of carbon so definitely it does not contain three moles of carbon and option C is Na atoms of hydrogen should not contain Na atoms of hydrogen it should contain four Na atoms of hydrogen so the option C is also wrong so the correct answer will be our option A. Moving on find the number of atoms present in 0.016 grams of methane now this is a very easy numerical after what we have done so far this should be homework you will do it on your own okay so please do this on your own and I'm telling you the answer the answer will be 0.005 Na okay so match your answer next question which has maximum number of oxygen now maximum number of oxygen atoms they have told okay let's see first one one gram of oxygen so one gram of oxygen means so definitely if it is oxygen we know that we can find out weight upon molecular weight is equal to N upon Na we can find out using this formula so one upon 16 is equal to N upon Na so how much is N coming Na upon 16 atoms okay very good option B one gram of O2 again do it one by now this time molecular weight of O2 will be how much 32 is equal to N upon Na so N here will be Na upon 32 and what is this N this N is molecules not atoms so you have to find out atoms one molecule of O2 contains two atoms so N molecules will contain how many atoms two N atoms just you have to multiply this thing with the atomicity so when you multiply it you will get two into Na upon 32 that will give you N upon 16 atoms again similarly do it for the C option one gram of O3 O3 molecular weight is 48 so one upon 48 is equal to N upon Na so here N is coming how much Na upon 48 this is again molecules you have to multiply this thing with atomicity in order to get the atoms so atomicity of O3 is 3 so Na upon 48 into 3 will be our number of atoms so this will again give the answer as Na by 16 atoms so can you see here also Na upon 16 here also Na upon 16 here also Na upon 16 so the answer should be our D all have same number of oxygen atoms next question 7.5 grams of gas occupies 5.6 liters at STP the gases we have to find W is given okay V at in liters at STP is given okay so we have to find out the molecular weight so weight upon molecular weight is equal to volume in liters at STP upon 22.4 now molecular weight let's take it as X so it will be 7.5 upon X is equal to 5.6 divided by 22.4 so X will be equal to 7.5 into 22.4 divided by 5.6 upon calculation how much will we get 30 so 30 is the molecular weight of which gas which gas over here this is 28 this is yes this is 30 so the option B will be the correct answer Na okay next question the maximum number of molecules is present in maximum number of molecules let's see one by one 15 liters of O2 at STP molecules they're asking so this formula we will apply N by Na is equal to volume upon 22.4 so N will be equal to 15 upon 22.4 into Na this is the first one for first first one this is option A then B it should come around N upon Na is equal to 10 upon 22.4 so N should be 10 upon 22.4 into Na okay this one is B see 1.5 grams of H2 so here which formula W by Mw is equal to N upon Na so here N will be equal to W is how much 1.5 divided by molecular weight of H2 will be 2 into Na this one is for C and for D it should be again this formula we have to use it should be 5 upon what is the molecular weight of CO2 for T4 that is equal to N upon Na so what will be N? N will be equal to 5 upon 44 Na now observe this values of N which one is maximum which one is more definitely definitely option 3 1.5 upon 2 Na so you can see the denominator is very very big over here so the value will be less but here the denominator is lesser so definitely this one will be our maximum number of molecules coming on to the next question a gaseous mixture contains O2 and N2 in the ratio 1 is to 4 by weight okay O2 is to N2 1 is to 4 let's take it as 1x 4x okay then the ratio of the number of molecules now taking this as weight we have to calculate the number of molecules so O2 first we will find out for O2 it will be 1x divided by 32 is equal to N upon Na so here N O2 we are getting how much x by 32 into Na this is for O2 similarly we will find out for N2 also here it will be 4x upon what is the molecular weight of N2 14 plus 14 28 is equal to N upon Na so what will be the total number of molecules of N2 it will be this we can cancel know with 7x upon 7 into Na now we have to find out the ratio of this and this so again O2 N O2 is to N N2 it will be x dot Na divided by 32 by x dot Na by 7 so this 2 will get cancelled giving the answer as 7 upon 32 so what should be the ratio 7 is to 32 which one is the correct answer option B option B will be our correct answer next question a sample of C286 has the same mass as 10 to the power 10 molecules of CH4 find the number of molecules of C286 okay W by Mw is equal to N upon Na this we already know this we already know can you see the relation between the number of molecules and molecular weight it is inversely proportional it is inversely proportional so can I write number of molecules of one sample upon number of molecules of second sample is equal to molecular weight of 2 upon right so using this formula we can calculate it very very easily I hope you have understood this how this particular thing is coming N1 is directly proportional inversely proportional to molecular weight of 1 N2 is inversely proportional to molecular weight of 2 now I have just taken the ratio of it okay now let's take one as this one and two as methane one is our ethane and two is our methane so N1 will be how much N1 will be we have to find out right the number of molecules of ethane we have to find out so let's keep as N1 N2 is how much 10 to the power 10 10 to the power 10 that is equal to molecular weight of 2 that is our methane over here that is 16 upon molecular weight of 1 the weight of ethane so that will be 30 C286 24 plus 6 30 so N1 is equal to 16 into 10 to the power 10 divided by 30 when we solve this the answer is going to come as 5.33 into 10 to the power 9 molecules this many molecules of C286 has the same mass as 10 to the power 10 molecules of CH4 final answer next question yes very important question very important question from 256 grams of SO2 one by one step by step we will go from 256 grams of SO2 now 256 grams of SO2 first I will convert it into moles let's take it at as N1 so N1 will be how much W upon MW that is 256 upon what is the mass molecular weight of SO SO2 it will be 64 so it will get cancelled with 4 so this is equivalent to N1 that is equal to 4 moles so from 4 moles of SO2 this many molecules of SO2 are removed again this molecules I will convert into moles again this I am taking as N2 it will be N upon NA so 1.2046 into 10 to the power 24 divided by NA so this particular thing I can write as 12 into 10 to the power 23 approximately divided by 6.023 into 10 to the power 23 this gets cancelled this will get cancelled with 2 so nearly equal to 2 so now rephrase the question from 4 moles of SO2 2 moles of SO2 are removed then find the volume of left over SO2 so what is the left over moles of SO2 left over moles of SO2 is equal to N1 minus N2 that is 4 minus 2 2 moles 2 moles of SO2 are left so what is the corresponding volume of this 2 moles of SO2 at STP N is equal to volume in liters at STP upon 22.4 so N is 2 so volume in liters at STP will be how much 2 into 22.4 that is our 44.8 liters so this much volume will be volume of SO2 will be left over at STP if we remove 1.2046 into 10 to the power 24 molecules from this 256 grams of SO2 this is a very important question same type of question can come here they can give a number of molecules they can they can vary it so here they can give N here they can give weight so first things first you have to convert it into moles it will be very very easier that time next yes now this is a integer type question how to do such questions read the question first five moles of AB2 okay five moles of AB2 contains not contains way 125 into 10 to the power minus 3 kg very good and 10 moles A2 B2 this is A2 B2 10 moles of A2 B2 weighs how much 300 into 10 to the power minus 3 kg okay very good again the molar mass of A and molar mass of B in kilojoules sorry kg per mole is this much okay so molar mass we have to find out of A and B okay first we will find out one mole of AB2 will weigh how much 125 into 10 to the power minus 3 upon 5 that will be 25 into 10 to the power minus 3 okay and one mole of A2 B2 will weigh how much 300 into 10 to the power minus 3 divided by 10 that will be 30 into 10 to the power minus 3 this is kg per mole this is also kg per mole per mole weight it is right so I can get two equations from here what are the two equations mass of A plus 2 into mass of B is equal to 25 into 10 to the power minus 3 this is the first equation and here 2 into mass of A you can see 2 2 atoms of A are there plus 2 into mass of B is equal to 30 into 10 to the power minus 3 very good this is equation 2 now what can I do I will subtract I will subtract 2 minus 1 I will do 2 minus 1 so if I do 2 minus 1 2 MA plus 2 MB is equal to 13 to 10 to the power minus 3 and MA plus 2 MB is equal to 25 into 10 to the power minus 3 subtracting this this will get cancelled this will give you 5 into 10 to the power minus 3 and MA so this value we have got MA is equal to 5 into 10 to the power minus 3 and they have told here molar mass of A is how much x into 10 to the power minus 3 so this is x so x will be our 5 let's find out what is MB so this equation I'm I'm taking so MA was 5 into 10 to the power minus 3 plus 2 MB is equal to 25 into 10 to the power minus 3 so 2 MB will be equal to 20 into 10 to the power minus 3 so MB will be equal to 10 into 10 to the power minus 3 and this was our y into 10 to the power 3 so we can say y into 10 to the power minus 3 so what will be our y 10 now what they're asking calculate the value of x plus y done x is 5 y is 10 so x plus y will be our 5 plus 10 that will be our 15 so 15 is the answer so this is how we approach integer type question next the number of moles of electrons which way 1 kg is 1 by x into 10 to the power 8 what is the value of x n i n i means nearest integer okay what was the mass of one mole of electron just now we have calculated it it was mass of one mole of electron can you remember it I told you to memorize the value it was 5.4 into 10 to the power minus 7 kilograms so I can say this many kilograms is equivalent to one mole so 1 kg is equivalent to 1 kg is equivalent to 1 upon 5.4 into 10 to the power minus 7 correct so now if I convert this into this particular format we have almost got the answer see this particular thing 5.4 into 10 to the power minus 7 if I write it like this 54 into 10 to the power minus 8 kg I can also write it like this no so then this will change 1 upon 54 into 10 to the power minus 8 which will be 1 upon 54 into 10 to the power 8 so this format and this format is matching now so our x will be 54 I'll repeat this once more so we have seen 5.4 into 10 to the power minus 7 kg is the mass of one mole of electrons change this format a little bit we can write it as 54 into 10 to the power minus 8 kgs that is equivalent to 1 mole of electrons so 1 kg will be equivalent to 1 upon 54 into 10 to the power minus 8 and from here this 10 to the power minus 8 is just going in the numerator this changing so x will be our 54 this is the final answer okay so the last question for today is the number of n atoms in 681 grams of C7H5N3O6 is x into 10 to the power 21 but this I will not solve this is for you to solve thank you so much see you in the next class