discuss mole ratios we need to talk about what can we get out of a mole ratio what does the mole ratio tell us and what can we do with it well first a mole ratio is telling us how many moles of one thing we have to another so we can actually get mole ratios in two spots we can get them from subscripts of chemical formulas so for example mgno3 this is called magnesium nitrate and what this tells me what this means the way this is written is i have one magnesium ion and two nitrate ions so for every one mole of magnesium nitrate i have three moles of ions i don't care what ion i just have three moles of ions right there i can also say i have two moles of nitrate to every one mole of magnesium two plus that is absolutely correct i can say i have six moles of oxygens to every one mole of magnesium nitrate that is really crowded in there i'm sorry also correct if i have exactly one mole of magnesium nitrate that contains six moles of water the other place i can get these multiple ratios is from balanced equations so here i see i've got two moles of c2h6 reacting with seven moles of water to produce four moles of co2 and six moles of h2o so these coefficients out front refer to the number of moles of each thing that's going to react so i could say 2 moles of c2h6 to 7 moles of o2 i can say 4 moles of co2 to 6 moles of h2o but i don't have to stay on the same side of the equation either i can say 7 moles of o2 to 4 moles of co2 i could say 6 moles of h2o to two moles of c2 h6 what does that mean we're going to talk more about that in chapter four we start bouncing equations but it means that looking at this for every two moles of c2h6 that i react i also react seven moles of o2 for every four moles of co2 produced i also produce six moles of water for every seven moles of o2 reacted i produce four moles of co2 for every six moles of water produced i react two moles of c2h6 and these can be used in calculations so how many hydrogen atoms are in 59.3 uh grams of water i apologize i will fix this before i give you guys your notes but this just to match your notes this should say 59.3 grams and i would normally just recalculate it for you guys but i don't have a calculator right in front of me so this should say 59.3 grams of water water is h2o and i know that water has two hydrogens and one oxygen go ahead and add up the molar mass and you should find the molar mass to be 18.02 grams per mole i want to know the number of hydrogen atoms so i'm gonna that is contained in 59.3 grams of water first thing i'm going to do is convert to moles when in doubt convert to moles if you don't know what else to do convert to moles most often you need to convert to moles anyway so converting to moles will help it'll help remind you what the next step is i'm going to convert this to moles so one mole of h2o contains 18.02 grams of h2o and note that cancels out my grams of h2o and now i have moles of h2o but i really want number of hydrogen atoms so in order to get to hydrogen atoms i first need to figure out how many moles of hydrogen do i have i know that there are two moles of hydrogen for every one mole of water because two moles of hydrogen go into making that one mole of water this cancels out my moles of water and now i have moles of hydrogen now that i have moles of hydrogen i can quickly calculate the number of hydrogen atoms so times 6.022 times 10 to the 23rd hydrogen atoms per 1 mole of hydrogen cancels out my moles of hydrogen i'm left with hydrogen atoms as i was targeting in the first place so this gives me 3.96 times 10 to the 24th hydrogen atoms again numbers that speak are hard to kind of check in your brains that make sense but i do know that 59.3 is greater than one mole of water and i know this number is greater i know there's two moles of hydrogen for every one mole of water so this number is greater than avogadro's number i believe we're on the right track how many nitrate ions are in 3.99 grams of aluminum nitrate well first you need to add up the molar mass of aluminum nitrate again in your notes i have this written as the name here i have the formula but this is called aluminum nitrate you learn naming in the very next chapter if you add up the molar mass of aluminum nitrate you should find it to be 213.0 grams per mole i want to know the number of nitrate ions contained in 3.99 grams of aluminum nitrate first thing i'm going to do is convert to moles of aluminum nitrate i know one mole of aluminum nitrate contains 213.0 grams of aluminum nitrate that cancels out my grams of aluminum nitrate and gives me moles of aluminum nitrate now i look back at the question i remind myself okay yeah that's right i'm trying to find the number of nitrate ions i see based on the formula that there are three nitrate ions for every one aluminum so i'm going to say times three moles of no3 minus to one mole of aluminum nitrate this cancels out my moles of aluminum nitrate and now i have moles of nitrate specifically now that i have moles of nitrate i can quickly calculate the number of nitrate ions using avogadro's number 6.022 times 10 to the 23rd nitrate ions in one mole of nitrate ions and my answer is 3.38 times 10 to the 22nd nitrate ions so 3.99 grams of aluminum nitrate contain 3.38 times 10 to the 22nd nitrate ions and our last example for this chapter unless of course you look at our additional practice possibilities is um so additional practice those are posted in a separate video and linked up on youtube um but the last example in this chapter how many ions are there in 15 grams of ammonium carbonate so note i'm not asking what type of ion i'm seeing ions as a whole you need to recognize here that ammonium carbonate has two ammoniums for every one carbonate which means it has three ions making up one mole of ammonium carbonate three moles of ions make up one mole of ammonium carbonate so i want to know number of ions contained in 15 grams of ammonium nitrate or ammonium carbonate ammonium carbonate so convert to moles how much does one mole of ammonium carbonate weigh you're gonna have to add that up so two nitrogens eight hydrogens one carbon three oxygens you should find the molar mass here to be equal to 96.09 grams per mole so grams of ammonium carbonate that cancels out my grams of ammonium carbonate and leaves with moles of ammonium carbonate now that i have molds ammonium carbonate i can convert to moles of ions i know i have three moles of ions for every one mole of ammonium carbonate that cancels out my moles of ammonium carbonate and leaves with moles of ions now that i have moles of ions i can use avogadro's number and calculate my final answer and i find that 15 grams of ammonium carbonate contains 2.82 times 10 to the 23rd ions again if you need extra help textbook online homework additional practice um videos are posted with all the additional questions at the end of this chapter please work these problems there's a lot going on review your objectives review the chapter focus and if you understand it all you'll be doing great