so what exactly is the mole what does that represent in chemistry it doesn't represent the animal it represents a number to illustrate it think of a dozen when you hear the word dozen what do you think of a dozen equates to 12 a dozen eggs mean you have 12 eggs a dozen calculators is 12 calculators a mole is similar to a dozen a dozen is equal to 12 but a mole represents a much larger number a mole represents 62 * 10 23 so if you have a mole of pens you have 6 * 10 23 P if you have a mole of pennies you have 6 * 10^ 23 pennies but typically the mole is associated with a very small particle like an atom a molecule a form unit within an ionic compound things like that now this number six times 10^ 23 that is also known as avagadro's number so what do we use this for typically you would use this for a conversion problem let's say if you know the number of moles of carbon atoms you can calculate the number of carbon atoms so let's say if we have four moles of car carbon atoms how can we convert it to the number of atoms so let's start with what we have four moles of carbon over one now based on the conversion that we wrote before one mole is equal to avagadro's number which instead of writing 6.02 I'm just going to round it to 6 * 10 23 and this is atoms of carbon so what's four * 6 * 10 23 4 * 6 is equal to 24 so we have 24 * 10 23 now if we move the decimal point one unit to the left this becomes 2.4 * 10 24 if you want your answer in scientific notation this number must be between 1 and 10 it can be equal to or greater than one but less than 10 another way you can see it is you can view 24 as 2.4 * 10 and we still have the 10^ the 23rd so if you multiply 10 the 1 by 10^ 23rd you need to add the exponents and that's why it changed to 24 so whenever you move the decimal point one unit to the left the exponent will increase by one so that's how many carbon atoms we have in this particular problem now you need to know when to use words like atoms molecules or formula units if you have carbon zinc neon these are composed of atoms if you have a H2 H2O C6 H6 these are composed of molecules a molecule is a particle that has multiple atoms now if you see something like sodium chloride magnesium oxide even though it has multiple atoms it's made up of ions whenever you have a metal and a non-metal it's an ionic compound and so therefore you would use the term formula units when dealing with molar conversions so let's say if we have five moles of methane convert it into molecules of methane because CH4 is a molecule it's a particle that has multiple atoms molecules are usually made up of nonmetals carbon and hydrogen are nonmetals if we had a metal and a nonmetal it would be ionic and we would use the term formula units so convert this into molecules of CH4 and also atoms of hydrogen so let's start with the first part so we have five moles of CH4 over one and using avagadro's number 1 mole is equal to 6 * 10^ 23 so we have 6 * 10^ 23 molecules now you want to set it in such a way that these units they cancel so now we can multip mly 5 * 6 5 * 6 is 30 so we have 30 * 10 23 and if we move the decimal one unit to the left the answer is 3.0 * 10 24 molecules of CH4 now how can we answer the second part of the question how can we convert molecules of CH4 into atoms of hydrogen one molecule of CH4 contains four atoms of hydrogen so we got to take our answer and multiply by four so 5 * 4 is 20 20 * 6 is 120 so we have 120 * 10 to the 23 so if we take the decimal point move it two units to the left this is the same as 1.2 * 10 25 atoms of hydrogen so sometimes you may need to take in another step if you want to go from molecules to atoms now let's try another example let's say if we have 4 moles of aluminum chloride how many formula units of aluminum chloride are there and also how many chloride ions are in this sample so let's start with the first part so 4 moles of al3 over one so let's convert it to formula units 1 Mo of al3 is equal to 6 * 10 23 formula units and the reason why we use the term formula units for this compound is because aluminum chloride is composed of ions it's an ionic compound aluminum is a metal chlorine is a netal whenever you have that it's represented in Formula units so this is going to give us the the first answer notice that the unit moles of al3 cancel so 6 * 4 is 24 so 24 * 10 23 is the same as 2.4 * 10 23 formula units now to find the next answer the number of chloride ions we could say that there are three chloride ions per one formula unit of al3 so 2.4 * 3 that's going to be 7.2 so we have 7.2 * 10^ 23 chloride ions and so sometimes you just need to take it an extra step further now what about working backwards so if we have 5 * 10 to the 24 actually let's say 3 * 10 24 atoms of hydrogen how can we convert it into moles of hydrogen so if you want to go from atoms or molecules or formul units to moles here's what you need to do start with the number that you have over one and then use avagadro's number but this time instead of being on top it's going to be on the bottom on top we're going to have the unit one mole of hydrogen so notice that the unit atoms cancel and so we just got to divide by avag God's number if you want to go from atoms molecules or formula units back to moles so 6 / 3 is 2 2 and 3 6 is 12 so we have 1/ 2 * 10 the power to notice that we have 10 24 / 10 23 when you divide common bases you need to subtract 24 - 23 is 1 so this is half * 10 half of 10 is 5 so we have five moles of hydrogen now the next thing you need to be able to do is you need to be able to calculate the M mass of a compound let's say if you want to find the M mass of c2h6 to do so you need to use the periodic table in a periodic table the atomic mass for carbon is 12 but there's two of them and for hydrogen it's one and there six so you get 24 + 6 which is 30 you can say 30 Atomic units or more commonly 30 G per mole go ahead and find the molar mass for the following compounds feel free to pause the video as you work out these examples sodium has an atomic mass of 23 and for oxygen is 16 for hydrogen is one so if we add these numbers we're going to get 40 G per per Mo now what about glucose C6 h126 so we have six carbon atoms each with an atomic mass of 12 12 hydrogen atoms and six oxygen atoms each with an atomic mass of 16 6 * 12 is 72 and 6 * 16 is 96 72 + 12 that's 84 84 and 96 that's 180 so the M mass is 180 g per mole now you can use the M Mass to convert from grams to moles so let's say if we have 34 gr of ammonia go ahead and convert that into moles so the first thing you need to do is you need to find the molar mass of NH3 nitrogen is 14 and plus three for the three hydrogen atoms so the molar mass is 17 so start with what you have 34 G of NH3 now the M Mouse is 17 G per mole so what that means is that one mole of NH3 has a mass of 17 G so you want to set it in such a way that grams cancel and you get moles on top so 34 ID 17 is 2 so it's 2 moles of NH3 that's how you can convert from GRS to moles you simply have to take the mass and divide it by the mle mass now let's try working backwards how can you use the M Mass to convert back to grams so let's say if we have three moles of neon convert it to GRS of Neon so let's start with what we're given 3 mol of NE over one now the atomic mass of neon is simply it's about 20 so what that means is that 20 G of neon is equal to one mole of neon so the units cancel and since we have two numbers on top we need to multiply so it's 3 * 20 which equals 60 G of Neon now let's make sense of it let's understand what the mass really is the m mass is the ratio between GS of moles so the M mass of neon is 20 so as we said one Mo of neon is equal to 20 G of neon that means 2 mol of neon is equal to 40 G of neon and so therefore 3 mol of neon is equal to 60 G of neon which is the answer to the question so that's another way you can uh solve that problem so how can we convert from grams to atoms so let's say if we have 12 gam of helium gas how many helium atoms do we have so if you want to go from grams to atoms you need to convert GRS to moles moles to atoms if you think you know how to do this feel free to pause the video and work out this example and then unpause it when you're ready to see the solution so let's start with 12 G of helium and let's convert it to moles the M mass of helium in a periodic table is about four so there's four G of helium per one mole and the way we set it up is we set up in such a way that grams cancel so now let's convert moles to atoms we know that one mole is equal to 6 * 10 23 the same way as a dozen represents 12 so the unit moles cancel so now let's do the math 12 / 4 is 3 and 3 * 6 is 18 so it's 18 * 10^ 23 so if we move the decimal one unit to the left this is the same as 1.8 * 10 24 atoms of helium so now you know how to convert from grams to atoms now what about going backwards atoms to GRS so let's say if we have 9 * 10 24 atoms of let's choose argon convert that to the grams of argon so let's start with what we're given 9 * 2 9 * 10^ 24 atoms over one so if you want to go from atoms to moles you need to put avagadro's number on the bottom so that the unit atoms will cancel and so we're going to have one mole of argon on top so the unit atoms will disappear now the last thing we need to do is convert moles to GRS so the mol mass of argon is like 39.95 but we're going to round it to 40 so there's 40 gram of argon for every mole of argon so these units will cancel so now we can do the math so it's let's break down 9 into 3 * 3 and 40 let's make it 20 * 2 and we have a six on the bottom a 10^ the 23 on the bottom and on top we have 10^ 24 now notice that 3 * 2 is equal to 6 so we can cancel these numbers so on top what we have left over is 3 * 20 which is 60 and now we can divide 10 24 by 10 23 which is 10 the 1 power 24 - 23 is 1 so we have 10 1 so we can leave the answer as 600 G or we can move the decimal one unit to the left and say it's 6 * 10 2 Gams but 600 gram is a nice number so we'll go with that so we have 600 gram of argon so now you know how to convert from atoms to grams so that is it for this video thanks for watching and have a great day