In this video you are going to learn how to calculate a compound's empirical formula. Alright, let's do this! Hello hello! Melissa Maribel here and I help students like you understand what you just learned in class so you stress less and graduate faster. Hit that subscribe button and we'll pass Chemistry together. Today's topic is on empirical formulas. An empirical formula is an educated guess or an approximation as to how many elements are within that chemical compound. It is not the exact chemical formula. Alright, there are multiple steps so let's jump right in. An unknown compound contains 68.4% of Chromium and 31.6% of Oxygen. Find the compound's empirical formula. First step is to change your % to grams. The reason we can just automatically do this is because if you were to add both of these numbers together you would get a 100%. So this entire compound or percentage is out of 100%. There's no need to convert anything. Literally change your % to grams if this is out of 100%. This is what we'll be using to do our next step. Step 2 is to convert your grams to moles. We'll use the grams from our previous step. Changing that to moles using the molar mass as your conversion factor because we're going from grams to moles. Aligning those grams across from each other so they can cancel and then we'll divide and we'll get 1.315 moles of Chromium. Do the same exact thing with Oxygen's molar mass. Divide these two values and we'll get 1.975 moles of Oxygen. Our next step, is to divide by the smallest number of moles. So our smallest number of moles was the 1.315 moles of Chromium. So we're going to do this for each moles and that will just cancel out our moles and we'll get some sort of subscript. So we now have 1 for Chromium and 1.5 for Oxygen. Your next step is to multiply these numbers, these subscripts to get a whole number. So in our case we have 1.5, we have a decimal ending in 0.5. So whenever you have any sort of decimal ending in 0.5 multiply each subscript by 2. There's another rule where if our decimal now ends with 0.33 or 0.66 multiply each subscript by 3. If we then have our decimals again that end in 0.25 or 0.75 multiply every single subscript by 4. So that's why in this case we're going to multiply both of these subscripts by 2 just because of this 0.5 value and that was the rule. So our final answer for our empirical formula would've been 1 times 2 which gives us 2 Chromium and 1.5 times 2 which gives us 3 Oxygen. This is our empirical formula. Now let's try one. I encourage you to keep practicing, keep trying. Don't give up. You will and you are completely capable of understanding these concepts and passing Chemistry. For more help check the description box below reserve your spot today for LIVE tutoring with myself where we're going to get into more and more detail with these concepts and we'll pass Chemistry together. Make sure you LIKE, subscribe, and I'll see you next time.