Stoichiometry Example 1

by Jules Bruno
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here in this example question. It says how many grams of h 20 are produced when 12.3 g of H two reacts. All right, so we know that they're giving us information on one compound in a balanced equation and asking for information on another. We know that is the definition of stock geometry. So we're gonna have to utilize this Don't geometric chart in some way to solve this problem. Now, if we follow the steps, it's a step one map out the portion of the Stoke geometric chart you will use from the question they're giving us 12.3 g of H two. Since that's a value they're giving to you that represents our grams of Given. So we're gonna start at grams of Given, which is just grams of h two, and we're gonna convert those grants into moles of Given. So moles of H two Now in the same question, they're asking us to find the grams of H 20 Since we don't know information on H two on, they're asking us to find it. This represents our grams off unknown. Okay, so that tells me I have to go for moles of Given and find a way to get 2 g of unknown. Now, at this point to go from moles of Given, I have to go to moles of unknown, and that is where it's required to do the job. So we're gonna go from moles of Given two moles of unknown. And then finally, we go from moles of unknown to grams of unknown. This is the path that we're gonna take to answer this question. So let's go to Step two, it says Convert the given quantity into moles of Given. And if a compound is said to be in excess, then just ignore it In this question, they don't say anything as being in excess. So we don't have to worry about this, uh, next line. Understand to later on, we'll come into situations where we're told something is in excess, and in that case, we just simply ignored. All right, so we're gonna take our given quantity, which is 12.3 g h two, and we're gonna convert it into moles of given grams of H to go on the bottom and one mole of H two goes on top H two has in it to hydrogen, and according to the periodic table, each one weighs 1.8 g. So that's 2.16 g grams. Here, cancel out and I'll have moles of H two, which comes out to 6.1012 Moles of H two. So I've just gone from grams of h two. So malls of H two. At this point, we have to do the jump. So going to stop three. It says to do a mole to mole conversion in order to convert moles of given into moles of unknown. So we take that 6. moles of H two to get rid of moles of H two. I put them on the bottom What am I looking for? I'm looking for my unknown My unknown is water So I need to find moles off h now remember to go from moles of given two moles of unknown That's called the jump and we do a multiple comparison The equation says that for every two moles of H two, I have two moles of H 20 So for every two moles of H two I have two moles of H 20 So here moles of H to cancel out. And now I have moles of H 20 So that's 6.1012 moles of H now finally, if necessary, convert the moles of unknown into the final desired units. Sometimes they may ask us to just find the moles of are unknown And in that case we'd stop for this particular question Though they're not asking us to find moles of water, they're asking us to find grams of water so an additional step is required. So 6.10 12 moles of H two Oh got to get rid of most of h two Also one mole of age tool on the bottom How many grams of h 12 do we have on top H 20 was composed of two hydrogen and one oxygen Hydrogen according to periodic table is 1.8 g. Oxygen is 16 g this is 2016 g and this is 16 g So the complete mass of H 20 is 18 016 g So we plugged that here Moles of water cancel out and now I'm finally gonna have grams of water. So here we're going to multiply those out. So that's 1199 g of H Now, technically, within this question, 12.3 has three significant figures. So technically, we should write this in three significant figures as well. So in scientific notation that will come out toe 1.10 times 10 to the 2 g of H 20 So this would be our final answer for this Tokyo metric question. So remember if we were given the amount of ah compound within a balanced equation and asked to find another, we're dealing with stoke geometry, which means you have to utilize this Tokyo metric chart in order to find your final answer.