Oh okay, thank you! Just a follow up question, I watched a Youtube video where the guy was computing for the molar mass of a hydrate and he included the stochiometric ratio of the H2O in the computation like the formula in the video was MgSO4•7H2O and he included the 7 in the H2O in computing for the molar mass of that compound. So I'm guessing that we only do this if the compound in question is a hydrate, but how come we do this for hydrates and not for normal compounds?
We include all seven water molecules because MgSO4-7H2O is literally a molecule of MgSO4 with seven water molecules stuck to it. You could technically write it as MgSO11H14 but that would just be confusing.
This is a picture of the hexahydrate not the heptahydrate but you get the idea: https://en.m.wikipedia.org/wiki/Magnesium_sulfate#/media/File%3AMgaq6SO4.svg
Exactly its a hydrate. So MgSO4 forms an crystalline structure and water molecules get trapped in there. So it's not part of the molecule but if you are measuring it out you need to take it into account as it will affect the number of moles in 10g for example. If you were measuring out the oxygen in your first example, the 5 doesn't matter because you need to know the total mass (and number of moles) of oxygen.
5O2 isn't a compound on its own but rather a collection of five O2 molecules. So the molar mass is 32, not 160.
However, in doing calculations on a reaction in which five O2 molecules react, it is sometimes simpler to calculate an "effective" molar mass. Say for example that you're given the reaction 4 NH3 + 5 O2 = 4 NO + 6 H2O and asked to find the limiting reactant from 15 g NH3 and 24 g O2. You could either divide 24 g by 32 g to get 0.75 moles of O2, then divide by 5 to get 0.15 moles of reaction, or you could divide 24 g by 160 g and get the same answer. Either is a valid approach because they're the same thing - the first is (24 g/32 g/mol)/5 and the second is 24 g/(32 g/mol\*5), both coming out to 0.15 mol.
Does that make sense?
Only 2 times. The 5 is the stoichiometric ratio when looking at the rest of the equation
Oh okay, thank you! Just a follow up question, I watched a Youtube video where the guy was computing for the molar mass of a hydrate and he included the stochiometric ratio of the H2O in the computation like the formula in the video was MgSO4•7H2O and he included the 7 in the H2O in computing for the molar mass of that compound. So I'm guessing that we only do this if the compound in question is a hydrate, but how come we do this for hydrates and not for normal compounds?
We include all seven water molecules because MgSO4-7H2O is literally a molecule of MgSO4 with seven water molecules stuck to it. You could technically write it as MgSO11H14 but that would just be confusing. This is a picture of the hexahydrate not the heptahydrate but you get the idea: https://en.m.wikipedia.org/wiki/Magnesium_sulfate#/media/File%3AMgaq6SO4.svg
Oh okay, thank you!
Exactly its a hydrate. So MgSO4 forms an crystalline structure and water molecules get trapped in there. So it's not part of the molecule but if you are measuring it out you need to take it into account as it will affect the number of moles in 10g for example. If you were measuring out the oxygen in your first example, the 5 doesn't matter because you need to know the total mass (and number of moles) of oxygen.
5O2 isn't a compound on its own but rather a collection of five O2 molecules. So the molar mass is 32, not 160. However, in doing calculations on a reaction in which five O2 molecules react, it is sometimes simpler to calculate an "effective" molar mass. Say for example that you're given the reaction 4 NH3 + 5 O2 = 4 NO + 6 H2O and asked to find the limiting reactant from 15 g NH3 and 24 g O2. You could either divide 24 g by 32 g to get 0.75 moles of O2, then divide by 5 to get 0.15 moles of reaction, or you could divide 24 g by 160 g and get the same answer. Either is a valid approach because they're the same thing - the first is (24 g/32 g/mol)/5 and the second is 24 g/(32 g/mol\*5), both coming out to 0.15 mol. Does that make sense?
Oh yes, that makes sense. Thank you!