hello everybody my name is Iman welcome back to my YouTube channel today we're starting our first topic for the high yield MCAT General chemistry playlist and the first topic that we're going to be discussing is mass atomic mass unit and moles now in chemistry the concepts of mass atomic mass unit and moles are connected and fundamental to understanding things like chemical reactions and the compos I of substances so first we're going to talk a little bit about each of these Concepts and then we're going to learn how they are related to each other how we can convert from one unit into another we will start by discussing atomic mass unit atomic mass unit is a standard unit of mass that quantifies the mass of atoms or molecules and it's defined as 1 12th the mass of a carbon 12 atom it is defined as 1 12th the mass of a carbon 12 atom which is an isotope of carbon with six protons and six neutrons the carbon 12 isotope it's stable and its abundance makes it a standard for measuring atomic masses one atomic mass unit is going to be approximately 1.66 * 10 to the - 37 kilog the atomic mass of an element which is what's usually found on the periodic table it's expressed in AMU and it represents the average mass of all the Isotopes of that element taking into account their relative abundance so that's atomic mass unit what about moles a mole is a unit that measures the amount of substance like the measure one dozen signals that you have 12 insert object right if you have 12 eggs you have one dozen eggs if you have 12 books you have a dozen books the same thing goes for a mole it's a unit that measures the amount of substance now one mole of any substance contains exactly 6.022 * 10 to the 23 entities this could be atoms molecules ions Etc this number 6.022 * 10 23r three is called avagadro's number the mole allows chemists to count particles by weighing them and the mass of one mole of a substance is equal to its molecular or atomic mass in grams and that leads us to talking about Mass specifically we want to talk about molar mass all right molar mass is the mass of one mole of a substance and it's going to be expressed in in G per mole now that we have defined these three terms how do we connect them all together and by that I mean how do we convert from one form into another so let's go over that using this figure right here as our frame of reference now let's say that you know the number of particles all right you know the number of particles but you want to convert that to moles how do you go from how do you go from number of particles and let me draw this better how do you go from number of particles to moles if you know the number of particles you can convert that to moles by dividing by avagadro's number all right so you can convert from number of particles to moles by dividing by avagadro's number all right right fantastic now what if you know the number of moles but you want to convert to number of particles so how do we get back the other way going from moles to number of particles here you want to multiply by avagadro's number okay fantastic what about if you know the moles and you want to convert to mass how do you do that well you can convert from moles to mass by multiplying by the molar mass that will convert your moles to mass what about going the other way around what if you know the mass and you want to convert to moles in that case you are going to divide by molar mass okay so far so good now what if you know the mass and you want to convert to number of particles so let's draw this Arrow over here going from Mass to number of particles how do you do that this is going to be a twostep process all right first you're going to divide by molar mass all right we're just following these smaller AR arrows here all right first you're going to divide by molar mass and then you are going to multiply by avagadro's number so if you're going from Mass to number of particles first you'll divide by molar mass and then you will multiply by avagadro's number so you are essentially just following two steps and it's going to be these two steps right here all right cool what if you know the number of particles and now you want to convert that to mass so going in the opposite direction well in that case you're going to follow these two arrows right here all right you're going to follow these two arrows and it's going to be a two-step process first you're going to divide by avagadro's number and then the second step you're going to multiply by molar mass okay fantastic let's try to apply that to a simple problem all right so here's the problem for us let's say that we have 3.11 * 10 23 particles of our argon all right this many number of particles of argon what are we trying to figure out what is the mass of argon in this sample okay so what's happening here what's Happening Here is we want to move excuse my alarm we want to move from number of particles all the way to mass and so we are going to follow this protocol right here we're going to divide by avagadro's number and then we're going to multiply by molar mass let's set this up all right so we have 3.11 * 10 23 particles of argon all right first step is we're going to divide by avagadro's number avagadro's number is 6.022 * 10 23 23 all right particles of argon is going to give you 1 MO of argon right that's our conversion when we talked about mole we said it's a unit that measures the amount of substance one mole here is going to be exactly 6.022 * 10 23 entities so that's our first unit of conversion we divided by avagadro's number and what you notice here is that the units for particles of argon cancel out okay cool now the second step is to multiply by molar mass the molar mass of argon is 39.95 grams per mole all right per one mole of argon all right what you notice here all right is that mole of argon cancels out and the only unit that's left is grams of argon that is going to be the unit that is associated with the number that we calculate based off of this calculation and that is going to give us the mass of this argon sample if you carry this calcul out you should get about 19.98 G of argon all right and so there we go we've covered our first topic Mass atomic mass unit and moles let me know if you have any questions comments concerns other than that good luck happy studying and have a beautiful beautiful day future doctors