hello during today's uh video we're going to be talking about mass percent now we've already dealt with mass percents before but now we're going to actually be able to use this idea of the mole and conversions between grams and moles and moles and grams to figure out the mass percent so everything that we've done before all of those examples that I came up with to give you and that you've worked I came up with those using the the method that we're going to be solving for here so let's take an example let's just quickly go through an example see how this works so let's say we have 88 02 G of carbon dioxide and we want to know the mass percent of carbon mass percent of carbon we know that the mass percent of carbon is going to be the mass of carbon divided by the mass of carbon dioxide mass of carbon dioxide all multiplied by 100% so this is the equation for mass percentage the mass of the element divided by mass of the sample uh times 100% that gives you the mass percent of that element now we were given the starting amount of carbon dioxide what we need to do is figure out the mass of this individual element in here so we had to do a few conversion steps to get to the mass of carbon so what we can do is we know as a chemist that we we we like the grams the unit of grams because we can weigh them out in downstairs in the laboratory however moles are much more important to us as a chemist we can convert a lot more different ways uh using the mole rather than G so let's take these these 88.2 G gr of carbon dioxide and convert it into GR of carbon and the way we do that is first we divide by the molar mass of carbon dioxide which is 44.1 G of carbon dioxide for 1 Mo carbon dioxide here we've canceled out the units of grams of carbon dioxide we're now into moles of carbon dioxide well now from here we can use the subscripts to identify the mleo mo conversion from the entire compound to the indiv idual element and since we're looking for carbon we're going to convert into carbon so for every 1 Mo carbon dioxide there's one mole of carbon our moles of carbon dioxide cancel now we're into moles of carbon the last step since we're trying to look for the mass of carbon is to convert from moles of carbon to grams of carbon we do that by multiplying by the atomic mass of carbon so for every one mole of carbon there's 12.01 G of carbon the mle of carbon cancel we're now left with gr of carbon if you plug this into a calculator you end up getting 24.02 G of carbon so now we know how many G of carbon are in 88.0 2 G of carbon dioxide for every 88.2 G of carbon dioxide there are 24.02 G of carbon now we have everything that we need to calculate the mass percent of carbon we have the mass of carbon which we calculated as 24.02 2 G of carbon we have the mass of carbon dioxide that was given to us at the start of the problem which is 88.2 G of carbon dioxide and we have the 100% is just a number times 100% if you plug this into a calculator uh and keeping four significant figures you're going to end up with 27. 29% is the mass percent of carbon so for every 88.2 G of carbon dioxide there uh the carbon has a mass percent of 27.29 per. now we've seen previously in the class that mass percents can be used in a lot of different ways and now we have another way of solving for mass percent so the great thing about Mass percents is it doesn't matter if I have 88.2 G of carbon dioxide 14 G of carbon dioxide 1 G of carbon dioxide any car carbon dioxide will have a 27.29 mass percent of carbon that will be for every sample of carbon dioxide so we're going to be doing a lot of problems like this in class just to get you aware of how we can use Mass percents it is a very popular technique in the world of General chemistry so we want to make sure that we understand how to do this as effectively as possible uh so with that I want to say have a great night I will see you all in class tomorrow