[Music] hello my dear students so how are you all I hope you all are doing well I am bhagan K Patel your dedicated chemistry faculty committed to guide you and prepare you for your KCT examination so today we will be discussing about the home assignment question on some basic concepts of chemistry so without any further wait let us start solving all the questions quickly so the question number one is two oxides are there of a certain metal and were separated in a current by passing what hydrogen until constant weight was obtained so here we are getting a constant weight of your metal atom because here water and water pres water will be obtained okay because hydrogen and oxygen from your metal oxide will combine and will give you water so this water is carefully collected and for one gam of each oxide if you take one gram of each oxide how many grams of water we are getting 0.2 G of water in first case and 0.4 G of water in second case so what does it it illustrates so it can easily you can say that if two oxides are present it contains metal and oxygen so there will be different ratio so it will be blow of multiple proportions simply but if you want to calculate also the proportions so you can easily do that for first oxide you can say that so the weight of oxygen present will be for first one it will be 0 .2 ided by 1 G you have taken and mass of oxygen is 16 and mass of water is 18 and in case of second month it will be 0.4 they have said mass of oxide is 1 and 16 ID 18 so it will be simply giving you 0.2 is to 0.4 ratios that means 1 is to 2 so therefore it is a simple multiple and hence law of multiple proportion next question statement one number of moles of hydrogen in 2.24 L of hydrogen is 0.1 Mo they are seeing so you know that 22.4 L of hydrogen consists of 1 mole then 2.24 lers of hydrogen will consist of how many moles it will be simply your 2.24 divid 22.4 it will be giving ra to 10 ra 2 minus 1 which is equal to 0.1 now statement two is saying 0 22.4 L of hydrogen at STP contains 6.23 into 10 to 23 moles of your hydrogen no it consists of 23 molecules of your hydrogen not the moles so it is your wrong option so therefore statement one is correct and statement two is incorrect next question the number of molecules of water in 3 333 G of your aluminium al2 so4 T aluminium sulfate 18 H2O if its molar mass is 6666 G so now we have to find the number of molecules of water in 333 G of this comp compound so in this particular compound you know that in one molecule if you take 18 number of your water molecules are there so in 1 moles how much it will be 18 into na then in 33 G how much it will be it will be simply n into na a into 18 so what is the number of moles given mass divided by molecular mass aad number and your a so how much it will be 3 1's are 3 2 are 6 2 9 are 18 so 9 into 6 into 10 23 option number B will be your correct option next question 224 mL of NO2 at STP was liquified see so 224 mL of NO2 is your volume of gas so Tate was liquefied and the density of liquid there say so of liquid is 2 2 G per ml calculate the volume of and number of molecules in liquid so volume they are asking in liquid how much it will be volume and how many number of molecules will be there so as volume in gas is given at STP you can first easily calculate number of molecules how you can do you know that number of molecules will be simply what number of moles into avocados number so how we will calculate number of moles now given volume 224 divided by how many volume at STP 20 2,400 and into avocad number is 6 into 10 to 23 so now it will be 100 and it will give us 10 ra to -2 23 / -2 is 20 1 so it will be 6 into 10 ra to 21 molecules would be there so in which option you have option number c clearly option number c was your correct option you know need to have done like further uh uh problem solving or calculation but still we will do it now so see here as the ml is for your gas now density is for your liquid so from density you know that density is equal to mass divid by volume so this mass of volume of liquid you can find from this formula but for that you must need Mass how much mass was there so you can calculate here so as you know that your 1 mole of NO2 consist of your 22,4 100 ml that means 46 G of your D nitrogen dioxide will consist of 22 22,400 ml then how much 22 224 ml will consist so it will consist of your 0.46 G correct so now just substitute there you will be getting your volume of liquid to be what it will be your mass divided by density so that is 0.46 divided density is 2 so 2 2 are 4 2 3 are 6 0 .23 ml you will be getting so the correct option is option number c 0.23 ml next question the number of molecules in 500 mL of each oxygen ammonia and carbon dioxide at STP r as you can clearly see volume is constant for every gas and at STP temperature and pressure is constant so therefore number of moles will be also equal for everyone as number of moles equal number of moles molecules will be equal correct so number of molecules will be equal therefore they have asked about molecules only so it will be the same order if you have asked atoms then you could have considered it consists of two atoms it consist of four and it consist of three so then the order might be NH3 then carbon dioxide and then oxygen if they have asked about atoms next question which of the following correctly represent 1,800 G of water they have asked so see you know that 18 G of water consist of 1 mole of your water so this Con contains the avocad number na a number of water molecule 6.23 into 10 ra to 23 molecules now 1,800 G of water they have given obviously it is equal to your 100 moles and if it is equal to 100 moles then how many number of molecules will be there number of moles 10 ra to 2 into your avocados number so the correct option is here 15 moles wrong 100 moles yes it is consist of 100 moles of water no here and here 10 23 + 2 25 so correct so option number two and four so therefore option C is correct next question consider the following reaction we have to consider this particular reaction and they have asked how many grams of HCL will react with 5 G of Manganese dioxide so see you can clearly see from this particular equation that your 1 mole of Manganese dioxide require 4 moles of your HCL that means 87 G of Manganese dioxide require 4 into 36.5 G of HCL then 5 G of Manganese dioxide will require how many gam of H so simply your X will be what x will be 5 into 4 into 36.5 divided by 87 so it will give you how much 8 .4 G so the correct option will be option number c next question consider element A and B so a has atomic mass uh atomic weight 12 and B has 35.5 A and B combines to form a compound X so if two moles of B combines with one mole of a so how many moles of B and how many moles of a in one molecule so that for a B2 is your molecular formula then the weight of 1 mole of x one mole of x X will be equal to summation of your atomic masses of elements present there so a is having 12 and B is having 35.5 therefore 2 into 35.5 it will be giving you 83 so the correct option will be option number B next question the law of conservation of mass can be explained by which of the following statements so we have to explain law of conservation of mass it talks about your summation of mass of your reactants will be equal to summation of mass of your product so this if it is explained with respect to your mass and the mass is given and it is proved then you will say that will explain your conservation of mass not just by statement so see 100 G of water is heated to give steam but how much steam we have obtained that we have to know a sample of nitrogen gas is heated at constant pressure without any change in its mass so change in mass has not occurred but still Mass we have to mention if 36 G of carbon combines 32 G of oxygen to form 68 G so here mass of reactants is equal to 68 and it will giving you 68 G of carbon dioxide so option C is clearly correct option next up a sample of calcium carbonate has the following percentage composition calcium 40% carbon 12% and oxygen 20 48% if the law of constant proportion is true then the weight of carbon in 2 G of calcium carbonate sample will be water so you can clearly say they are asking about if there is a 2 G of calcium carbonate then how many grams of carbon will be there now from given you go with carbon percentage so in 100 gr of your calcium carbonate they are saying 12 G of carbons will be present so then what will be the value of x simply so X will be equal to 2 into 12 / 100 so it is equal to 24 by 100 so it is 0.24 G so correct option will be option number B next question the following data are obtained when D nitrogen and di di oxygen react together to form a different compounds so different compounds are formed using nitrogen and oxygen as a sole element so now there is a proportion of mass will be different but the elements are same so law of multiple proportion can be applied but still we have to see whether it is working or not we are getting a ratio or not so what you can do is you can consider any of these oxygen or Nitro D nitrogen take constant Mass so here there is 28 28 I will consider this also 28 multiply by two If I multiply this by two this will also get multiplied so here it will be 16 2 are 32 64 80 and 6 so what is the ratio 16 1's are 16 2 are 16 4S are 165 are so it will be 2 is 4 is to 5 is to 1 so are we having a simple multiple ratio of oxygen present in your nitrogen Mass correct so therefore law of multiple proportion next question 50 to unified mass of helium contains how many number of atoms so see whenever you are defining mass in terms of unified Mass it is talking about your one atom only so if you say four unified mass of your helium atom then it tells about one atom of helium Mass so one atom of helium it will correspond to if you talk about 4 G of helium then it corresponds to how many atoms any atoms understand the things separately but here unified Mass therefore 52 unified mass of helium will consist of how many atoms it will be just 52 / 4 which will be equal to 30 so correct option will be your option number B next question which of the following is the correct order of your increasing weight we have to compare the weight here so now here first here let us take a what they have given 0.625 G of your iron so already they have given you weight for next one they have given 0.0105 equivalent of H2 c204 2 H2 so equivalent can be converted into grams how you have to write equivalent and equivalent weight so what will be the equivalent weight molecular mass divided by your valency there are two replaceable hyr iion valenc is two molecular mass will be equal to 126 so now it will corresponds to 0.66 G next if you take this one that is your zinc so 6 point 10 R to 21 atoms are there it is say so you know that 6 into 10 ra to 23 atoms will present in 1 mole that is 108 G uh sorry sorry sorry it will be present in 1 mole of Z correct then 6001 into 10 to 20 1 G will be containing how many moles we have to calculate so rather than taking mole what we can do is we can take this directly into the mass so you can write 6 into 10 ra to 23 consist of your 1 mole of your zinc consist of how much mass so Mass it will be 3 65 so now 65 so into 10 to 21 will consist of X now x value comes around 0.647 now let us talk about your silver which is given here so here carefully see gr atom is given so you know that 1 G atom is equal to 1 mole correct so therefore 1 G atom of your silver will consist of 108 G so 6 G atom of silver will consist of how many G so X will come around 0.648 G so now if you consider the mass which one will be the having the highest mass here 0.66 it is the highest so first one this one and where you have another option where it is the highest one no option so option number B is clearly the winner and next it is your 0.648 that is of your silver silver then zinc and then comes your uh yes iron next question which of the following contains the highest number of atoms they have as so how you will calculate number of atoms so number of atoms can be calculated by number of moles aatos number into number of atoms present in a molecule correct so number of moles can be written as weight divided by molecular mass into na into number of atoms if you carefully observe here your mass is given as a constant so now you will just consider the ratio of your number of atoms divided by m mass and na will be a constant just okay so write the ratio for each of the following cases so for first one what will be the ratio here it is number of atoms is having 14 and what is the molecular mass 58 for second one what is the molecular mass 28 and how many atoms there two atoms and in the next case how many Mar Mass 108 how many atoms one atom M Mass 18 how many atoms three so now if you take the ratio here it will come around uh around 14 4 point something it will come and here 2 1 are 2 uh 2 4 are 8 14 it will come and here 3 1 are 3 18 six so now which one is having the least denominator having the most value correct so least denominator is for First Option so therefore its number will be very high so option number a will be your correct option next if 0.8 mole of carbohydrate with empirical formula ch2 has 10 G of hydrogen then molecular formula of carbohydrate will be water so clearly see we have we know that here the in which emperical formula ch2o has 10 G of hydrogen then what then molecular formula of carbohydrate will be what they are asking so here you have 0.8 mole of let's say empirical molecular formula to be n * has how many G of hydrogen 10 G of your hydrogen then for one mole of your hydro carbohydrate how many grams of your hydrogen you will be obtaining that you have to find so what the value will be so the value will be x value will be 10 / 0.8 correct so 10 divid by 0.8 gives you approximately 12 value so now 12 G of hydrogen is present in one mole of your ch2 so now let us take just the number of um um empirical formula and molecular formula mass to calculate n value so n will be mole in molecular formula what is the mass of hydrogen to in empiric formula what is the mass of hydrogen 2 so it will give you six so here it will be six therefore C6 h126 so option number a will be your correct option next question in 2.8 L of a diatomic gas so diatomic gas means your number of atoms will be equal to two at STP the number of molecules respect molecules and atoms respectively or they have as so see you know that 22 4 lit consist of your na atoms na sorry molecules so if it is consist of Na molecules and it is diatomic the number of atoms will be 2 N correct so now the given volume is here 2.8 L then 2.8 L consist of let's say x molecule then what will be the number of atoms 2x correct so let us find the first value of x x will be simply what it will be 2.8 into na a / 22.4 correct so if you take one unit at that side so you will be getting what 2 On's and here it will be uh 28 are so 1 divid by 8 and8 will be giving 0.75 into 10 to 23 so how much it will be 7.5 into 10 to 22 so now what will be the mass of uh number of atoms here 7.5 into 2 therefore 15 into 10 to 22 so the correct option will be clearly option number c next question the density of the liquid liquid's density is 1.2 G per ml if there are 35 drops in 2 ml then the number of molecules in one drop will be water so to calculate this what we have to do first you know that density is nothing but it is equal to mass divided by volume correct so you know the density and if you know the volume you would know the mass correct then you just divide how many number of molecules how we calculate you will be calculating it by number of moles into your na so it will be just weight divided by molecular mass into na so for that weight you need so to calculate Weight Mass you need the volume so how you do see here so if 35 drops corresponds to 2 ml then one drops corresponds to how many ml so here x value comes around 2 / 35 ml now you got volume so you substitute in this formula what will be the mass now so here mass will be equal to density into volume divided by marar mass into n so density is 1.2 volume is 2 / 35 and marolar mass is given 70 into na so 2 1's are 235 are so we can clearly say 1.2 / 35 whole S NA so the correct option will be your option number c next question an element X is found to combine with oxygen so there is an element X it is combining with oxy to form a compound with the molecular formula x46 now they are seeing if 8 G of element combine with 6 G of oxygen what is the atomic weight so what they have given eight G of X combines with what 6 G of oxygen correct now you if you carefully see this molecular formula you know that 4 into atomic mass of your X combines with how many gr of oxygen so 6 into 16 G of your oxygen correct so you can clearly calculate the value of atomic mass from here so what it will be so atomic mass of X will be be equal to 8 into 6 into 16 / 6 into 4 correct 4 4 28 six six cancel 16 2 are 32 so therefore option is B next question the maximum number of molecules is present in which of the following options so the maximum number of molecules they have asked so how how we calculate number of molecules number of moles into na a correct so number of moles how we calculate it will be either equal to weight divided by molecular mass if it is in gas at STP it will be given volume divided by 22.4 L into na just do it so here in the first case what you will do you will take 15 divided by 22.4 L ratio in this case 5 divided 22.4 L and in this case 0.5 divided by what is the mass of hydrogen 2 and in this case you will be taking 10 ided by 16 2 are 32 correct so now what is the mass you will be getting here so the for first case so first is 15 ided by 22.4 so here you will be getting Mass has to be 0.6 and here you will be getting it will be equal to 1id 4 0.25 and here also you'll be getting 0.25 and here if you take uh approximately the 30 and it will be 100 divid 3 0.33 so which is having the highest number of moles option number a so option number a will be your correct option next question if na is avocad number then what will be the number of veence electron present in 4.2 G of your nitride ion so let us consider this nitride ion they are talking about 4.2 G of nitride ion veence electron how much it will be so it will be just number of moles into avocados number into what you will be doing you will be doing number of electrons in your bence shell so number of moles how much it will be given Mass 4.2 and what is the molecular mass of your nitrogen 14 now what is the number of valence electrons present in your nitr so valence electron five and there is minus three charge so eight so 8 into n correct and what will be the value now here it will be giving you 2 .4 na so correct option will be your option number B okay next the 1 ml of N2 at STP contains how much so 1 ml of N2 they are asking and they have given answer in terms of atoms electrons and molecules correct so how you will calculate see so your 22,400 ml consist of of your n a number of your molecules and how many atoms it will be there so 3 into n a number of atoms and how many electrons will be there so if you take here nitrogen consist of seven 7 7 2 14 and 14 + 8 22 so 22 into na a electrons will be there so just you do for each case so now what will be the number of molecules now so 1 ml divided by 22,400 into your 6 into 10 ra23 correct so this option is given molecules is correct yes it is correct next here it will be 1 ml ided by 22,400 ml into 3 into 6 into 10 to 23 6 6 6 3 are 18 and here 22.4 so you can write 1 / 2 2 2 4 into your 10 ra to 22 so is it correct given yes it is correct now for this case how much it will be 21 ided 22,400 into 22 into 6 into 10 ra to 23 so how much it will be 132 ided 22400 into 10 ra 223 and now uh decimal point to 13.2 22.4 four correct so option number c is also correct so therefore all of these are your correct option next question an impure sample of silver so there is a sample of silver here which is an impure so how much gram you have taken 1.5 G is heated with sulfur to form 0.212 G of your ag2o okay so silver is there it is heated with sulfur and you are getting AG 2s so 2 moles of of AG is used what was the percentage yield of your AG to S here there have been asked you so what you can do here is so first let us initially understand what must be the your yield okay so what will be the a according to you so here a impure sample of 1.5 G of silver is taken to form how much they are seeing 0.12 G so this is will not take let us identify for 1.5 G how much gam of H2S has to initially form so from this particular equation you can clearly say that 2 mol of silver 2 into 108 G of silver must give 1 mole of H2S that is 248 G of your ag2s it must be giving so then what will be the value of x so from this following equation the value of x will be 1.5 into 248 divided by 2 into 108 correct so 2 into 108 it will be giving you 0.12 something correct uh uh 2 1 2 2 are 2 4 are 8 124 it will be giving and it will be giving you 0.12 now 0.12 you have got now it sorry sorry sorry sorry so here the mass of X will be equal to 1.5 into 248 ided by 2 into 108 so how much mass you should have got 2.6 G you should have got so this is the actual mass you should have get how much you have got 0.12 you have got so then percentage yield will be simply how much you have got actually and how much actually you should have get into 100 so it will give you around your 6 percentage nearest Value so 6 per nearest value for which one you are having you are having for your option number B next question a mineral has the following composition so you have a mineral which consists of your magnesium oxide silicon dioxide and water with how many percentage they have given so with 31.8% 63.37-inch are 32 and it will be giving you 60 and water if you take 4.75 / 18 so how much value will be getting so for first case you will be getting around 0.79 and for the second case 63 divid 37 you can clearly say it will be giving you 1 something 05 and for 4.75 divided by 18 it will be giving you around your 0.26 something so the least ratio will be 3 4 and 1 correct so 0.26 I will divide by each cases so here you can see the empirical formal least formula will be like this mg T si2 4 * and H2 is one time so you can say mg is three how many hydrogen are present hydrogen is 2 H2 then magnesium how much three next silicon how much four oxygen how much 4 2 are 8 9 9 10 11 12 so correct option will be your option number D next question the minimum amount of oxygen consumed per atom of your reactant in which of the following reaction so they have asked about minimum oxygen where it will be consumed so in all the cases you can clearly see here so what you are seeing four moles of C for one thing I will do and next we'll find the least ratio okay so for this one four moles of iron required 3 moles of your oxygen so four moles of iron means 4 into 56 gam of your iron requires how many moles of your oxygen actually requiring your three into 32 G of your oxygen correct so the minimum oxym consumed per gram of reactant they have asked so for 1 G how many it will be there so here the least ratio you can find in terms of just X will be equal to 3 into 32 G of oxygen required divided by how many gram of iron you have taken so for every case if you do this ratio you will be getting so now for option b just move directly so how many grams of oxygen here 32 so how many grams of magnesium here 2 into 24 and then next case how many G of oxygen is present here 5 into 32 how many G of phosphorus is present 31 into 4 next in this case how many gr of oxygen 5 into 32 next what is the mass of C3 h8 so carbon is 12 12 24 plus here eight correct so now if you talk the least ratio here so here 32 you are getting so if you divide it by 1 3 1's 3 1 3 one carry here 515 point something you will be getting so here 32 divid 4 into 15 you are getting so in this case what you are getting here so 5 6 are 30 around something 6 point something will be there now here 32 is there similarly and here if you take it is uh 32 54 + 8 you will be getting around uh 32 divided by 6 something you will be getting so now you can can clearly see that which is having the highest denominator that will be having the lowest value of your oxygen so highest denominator is for water 15 into 4 6 into 4 or 6 or 2 into 24 which one is having your highest value of your denominator obviously first case so option number a will be your correct option next question which of the following statement is incorrect they have asked gr atomic mass of an element may be defined as a mass of avocados number of atom yes when we are saying gr atomic mass it is talking about one mole of your uh one mole of your compound and one mole of your compound nothing but your avocad number the molecular mass of diatomic Elementary gases twice its atomic mass yes it will be two into atomic mass twice so gex chemical combination is valid for all substance no it is not valid for all substance it is valid for only your gases next a pure compound has always a fixed proportion of mass of its constitute yes it has a fixed proportion of your mass so option C is your wrong option next question what is the marity of h2so4 solution that has a density of 2.84 G of CC so that density is given that of your solution and the weight is given by 98% by weight so if 98 percentage by weight is given you can clearly say that 98 G of h2so4 in your 100 G of your solution so we have have to calculate marity correct so marity will be equal to what number of moles divided by volume in a liter we have to find Now volume correct so you got number of moles to be 98 G and molecular mass 98 into volume we need so from density you can get volume that is mass divided by volume so what is the mass here volume will be equal to mass is 100 G for solution so 100 what is the density given 2.84 correct so it will be equal to here 100 multiplied by 2.84 and it is in ml so that's why you will multiply by th000 again so here 20 two 0 got cancelled and here 98 98 got canceled you will be getting 28.4 mol so correct option will be your option number c next question among the following pairs of compound the law of multiple proportion is illustrated by for law of multiple proportion only two types of element must be there but in different Mass ratio correct so here H2S hydrogen sulfur and oxygen three types of there nothing it is not possible then berum oxygen and chlorine three are there no nitrogen hydrogen and oxygen three are there no nitrogen oxygen nitrogen oxygen different ratio option number D next question ation one mole of sulfur dioxide contains same number of molecules present in one mole of oxygen so they are saying if one mole of sulfur dioxide of any gas you are taking then the number of molecules present in one mole of same oxygen will be same yes if number of mool same number of molecules will also be same assertion is true molecular weight of your sulfur dioxide is two times that of your oxygen so molecular weight of your sulfur if you calculate 32 + 16 2 are 32 it will be and here that is two times of it is 32 correct so here if it is 64 and it is 32 it is saying that it is two times of your mass mass of oxygen yes obviously it is true but is it the reason for your assertion for same number of molecules no if number of moles is same then number of molecules are equal that has to be explained in the case of reason so you will say both assertion and reason are true but reason is not the correct explanation of your assertion next question use the data given in the following table to calculate mol mass of naturally occurring Argan so naturally occurring Argan is there this question is very simple you know that how you will calculate percentage abundance into your Mar Mass you will calculate summation and divide by 100 you will do correct but in this case what you can do here in examination is first see the options which have given so if options are far apart so they are far apart and now see the table so now see the percentage which one is having the highest percentage so here you can see 99% of something is 39.9 G of Isotopes only so obviously the mass will be nearest to this value so it will be obviously option number B okay so the next question next question 40% of volume weight divided by volume of NAC so that means 40 G of NCL is present in what 100 ml of your solution okay so the specific gravity is 1.20 is equivalent to water so they have asked about your PPM so so for PPM how you can do is parts of your solute divided by your solution part you will take and then you will multiply by 10 the^ of 6 so solution you can get from your specific gravity that will give you mass of solution to be your volume of your solution into your specific gravity you have to take 1.20 so it will be 100 into 1.20 you'll be getting 112 so here if you substitute what you will be getting 40 / 112 into 10 6 you will be getting here uh 0 0.35 so it will be 3.5 into 10 to 5 PPM so the correct option will be 10 to 5 PPM option number a so I hope you have understood all the solutions so practice well all the best thank you