[Music] hi there in our previous lesson we talked about the mole concept to express massive substances in this video we will talk about how to determine the percentage composition of a compound given its chemical formula and vice versa if you still haven't watched the previous lesson you can pause this video and watch that one first to better understand our lesson today imagine yourself taking a test and getting a hundred percent remarks on your test result what does the hundred percent mean it means that you got all items correct and have a perfect score you may have gotten 10 over 10 or 20 over 20. the 100 is called the percentage score if you want to get your percentage score in a test you simply divide your score over the total test items and multiply it by one hundred for example we have twenty over twenty times one hundred equals one hundred percent now why do we need to multiply the percentage score by one hundred this is because percentage would also mean an amount in hundred or by a hundred [Music] the percentage composition of any given compound is identified as the fraction of the amount of each element on the total amount of individual elements present in the compound multiplied by 100 it is simply an expression of a compound's composition in terms of all the elements present knowing the percentage composition in a compound is useful in determining the empirical formula of a chemical substance which will be discussed in higher grade levels the percentage composition of a compound can be determined from the chemical formula of a compound the formula to be used is percentage composition equals mass of element in one mole over molar mass of a compound times 100 percent from the given formula you can get the percentage composition by knowing the following data first one the elements present in the compounds two the atomic mass of each element three the number of atoms of each element and lastly the molar mass let's try this sample problem muriatic acid also known as hydrochloric acid is used as a cleaning agent in homes to get rid of tough stains and molds calculate the percentage composition of muriatic acid i'm going to list down some steps to better understand the calculations step 1 list the known and unknown quantities the known quantities are mass of hydrogen in one mole which is 1.001 grams and mass of chlorine in one mole which is 35.45 grams note that these can be found as atomic mass from the periodic table of elements lastly when we add the two elements we can get the molar mass of hydrochloric acid which is equal to 36.45 grams per mole next we're going to look for the percentage of hydrogen and chlorine step 2 calculate the percentage composition of each element by dividing the mass of each element by the molar mass of the compound and multiplying by 100 percent percentage of hydrogen equals 1 gram of hydrogen over 36.45 grams times 100 percent equals 2.74 of hydrogen percentage of chlorine equals 35.45 grams chlorine over 36.45 grams times 100 percent equals 97.26 percent of chlorine last step step 3 review your result it should total to 100 2.74 of hydrogen plus 97.26 of chlorine equals 100 therefore hydrochloric acid is 2.74 percent hydrogen and 97.26 chlorine that was the first way of getting the percentage composition through its chemical formula the other way is from its given mass data [Music] percentage composition can be calculated given the masses of each of the elements present in a compound we will still use the same formula with little changes instead of massive element in one mole it will be mass of given element and instead of molar mass of compound it will be massive compound let's try another problem a certain newly synthesized compound is known to contain elements zinc and oxygen when 30 grams of the sample is decomposed 24.12 grams of zinc remains determine the percentage composition of the compound first list the known and unknown quantities the given quantities are massive compound which is 30 grams and massive zinc which is 24.12 grams we're going to find the percentage of zinc and percentage of oxygen [Music] second calculate here's a hint subtract to find the mass of oxygen in the compound divide each element's mass by the total mass of the compound to find the percentage by mass mass of oxygen equals 30 grams minus 24.12 grams of zinc equals 5.88 grams of oxygen now we have both the mass of zinc and oxygen percentage of zinc equals 24.12 grams of zinc over 30 grams times 100 percent equals 80.40 zinc percentage of oxygen equals 5.88 grams of oxygen over 30 grams hundred percent equals nineteen point sixty percent oxygen lastly review your result it should total to one hundred percent eighty point forty percent zinc plus nineteen point sixty percent oxygen equals one hundred percent the calculations sound reasonable because this adds up to a hundred percent and you can see in the result that by mass the compound is mostly zinc with 80.40 percentage composition now let's wrap things up the percentage composition is simply an expression of a compound's composition in terms of all the elements present there are two processes in determining the percentage composition of a compound first by calculating given the chemical formula of the compound and second given the mass data of the compound knowing about percentage composition is very significant in determining the empirical formula of a chemical substance that's all for now see you on our next video and don't forget to keep your minds busy if you like this video please subscribe to our channel and hit the notification icon for more videos like this