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Acmlm's Board - I2 Archive - General Chat - Mole confusion (Chemistry) | | | |
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Yoshi Dude XKEEPER STOLE MY CAR KEYS Level: 79 Posts: 1601/3271 EXP: 4572680 For next: 6787 Since: 03-15-04 From: give me a number folks. Since last post: 3 hours Last activity: 2 hours |
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I need help on some Chemistry problems I have to do. I wont throw out every problem to you guys, just a few. I'm real confused. I showed my mom and she said moles was the reason why she didn't do well in the class herself. Stuff to know (we round the numbers in my class) 6x10^23 particles/mole Ne: 20.2g molar mass Osub2: 32.0g molar mass I don't know if molar mass adds anything to these problems. How many moles in 5.2 x 10^23 atoms of Ne? How many atoms in 3 moles of Osub2 molecules? Now I don't just want the answer, I can get that, I need to know how to find it. I don't understand the relationship between grams, moles, particles, molecules, or atoms. Like, I know there's some formula that will let me do all of these problems but I just don't know what it is. I figure if I know how to do those two problems, I can do the rest. I really appreciate any efforts, I'm barely getting an A in the class and if I get these wrong it'll shoot me down for sure. |
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hhallahh Bob-Omb Level: 38 Posts: 388/607 EXP: 365476 For next: 4971 Since: 03-15-04 From: Portland, OR Since last post: 73 days Last activity: 60 days |
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The molar mass of an atom/molecule refers to how much 6.02*10^23 units of that compound weighs, in grams. For the first question, you have to divide Avagadro's (sp?) number (6.02*10^23) by 5.2*10^23.. think of it as if I asked you, "If there are 100 centimeters in a meter, how many meters is 35 centimeters?" It's a simple conversion, and you should be able to do that kind of question easy. I recall in Chemistry they made us write it out as: ((5.2*10^23 atoms Ne) / 1) * ((1 mol Ne) / (6.02*10^23 atoms Ne)) = ? The first part of the equation simply writes out what you're starting with, 5.2*10^23 atoms Ne. The second part is a conversion. 1 mol Ne = 6.02*10^23 atoms Ne by definition, so you multiply your starting point by that conversion in order to get the answer. That might not be sufficiently clear, but it's hard to show without writing it out on binder paper.. The second equation's conversion can be written out as: ((3 mol O2) / 1) * ((6.02*10^23 molecules O2) / (1 mol O2)) * (2 atoms O / 1 molecule O2) = ? Again, note that the first part of the equation is simply your starting point. The second part is the conversion from mols O2 to molcules O2... 1 mol O2 = 6.02*10^23 molecules O2. Also note that since there are 2 Os in every O2, another conversion of 2 atoms O2 = 1 mol O2 is needed to derive the total number of O. All conversions will have this format.. to go back to the simple example I used above: ((35 centimeters) / 1) * ((1 meter) / (100 centimeters)) = .35 meters The first part is my starting point, the second is the conversion of 100 cm = 1 m. See the pattern? (Geez.. so many edits. I'm sloppy about this.) (edited by hhallahh on 10-11-04 12:04 AM) (edited by hhallahh on 10-11-04 12:04 AM) (edited by hhallahh on 10-11-04 12:06 AM) (edited by hhallahh on 10-11-04 12:11 AM) (edited by hhallahh on 10-11-04 12:11 AM) |
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Arwon Zora Level: 35 Posts: 168/506 EXP: 278115 For next: 1821 Since: 03-15-04 From: Terra Australis Incognita Since last post: 5 hours Last activity: 10 min. |
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It's been a few years since I did chemistry but let's see what I remember: A mole is just a particular number. Like "a dozen" is 12, "a thousand" is 1000... "a mole" is 6x10^23. So Ne, having a "molar mass" of 20.2 grams, that means that 6x10^23 atoms of Ne weighs 20.2 grams. O2, meanwhile, has a molar mass of 32 grams, meaning that 6x10^23 molecules of O2 weighs 32 grams. It doesn't make a bit of difference whether it's atoms or molecules - you can have a mole of either. It just depends on whether the substance is an element made up of single atoms, or a compound made up of molecules. Moles are just a way to count particles, it doesn't matter whether those particles are single atoms or molecules. For the first question it looks like you just have to figure out what percentage of 6x10^23 the number given (5.2x10^23) is... the answer should be something a little under 1 mole. For the second, you need to first figure out how many atoms are in ONE mole of O2. The key is that they want atoms, not molecules. Think about what O2 is. It's a molecule consisting of two oxygen atoms. So in 1 mole of O2 there is 6x10^23 molecules, meaning there is TWICE as many atoms. So how many atoms in 3 moles of the stuff? (edited by Arwon on 10-11-04 12:05 AM) |
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Yoshi Dude XKEEPER STOLE MY CAR KEYS Level: 79 Posts: 1602/3271 EXP: 4572680 For next: 6787 Since: 03-15-04 From: give me a number folks. Since last post: 3 hours Last activity: 2 hours |
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Thanks you guys. Okay, so for the first problem 5.2*10^23/6*10^23 = .87 mole. Yeah? The second one I'm a bit more confused on. So a mole of O2 molecule has 12x10^23 atoms in it, twice as much? So that would be (12x10^23)3 = 36x10^23 atoms Yes? |
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hhallahh Bob-Omb Level: 38 Posts: 389/607 EXP: 365476 For next: 4971 Since: 03-15-04 From: Portland, OR Since last post: 73 days Last activity: 60 days |
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Originally posted by Yoshi Dude Yea, that's right. I don't know if you're learning the same conversion format that I did, but the way I write out the problems is very simple and if you can follow it, then you should be able to do any conversion your teacher could throw at you. |
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Arwon Zora Level: 35 Posts: 170/506 EXP: 278115 For next: 1821 Since: 03-15-04 From: Terra Australis Incognita Since last post: 5 hours Last activity: 10 min. |
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I feel it's more important to understand what you're doing than just learn conversion formats - they can come later. The danger with just learning formulas is inflexibility and inability to approach an unusual problem logically. Understanding what a mole is - an arbitrary number of particles chosen to make it possible to mathematically deal with particle weights in the macro world (you can't see 1 atom and compare it with another type of atom, but you can see 6x10^23 of them and compare them to 6x10^23 of another type) - is also important. |
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NSNick Laidback Admin Level: 85 Posts: 1217/3875 EXP: 5895841 For next: 2699 Since: 03-15-04 From: North Side School: OSU Since last post: 9 hours Last activity: 1 hour |
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It's also helpful to use unit analysis. If after the units cancel out, you have the unit you're supposed to, that's a good sign. For example, in that first problem: How many moles in 5.2 x 10^23 atoms of Ne?
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kiwibonga Double metal axe Level: 27 Posts: 227/266 EXP: 106040 For next: 10119 Since: 03-15-04 From: Montreal, QC, Canada Since last post: 126 days Last activity: 3 days |
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I got through most of high school chemistry and physics without learning formulas... They give you 3 variables and tell you the unit the answer is in, that problem is another one of those where you can figure out the formula just by knowing the units. Molar mass => Molar = mol, mass = grams ; since it's molar mass, and not... massic? massal? wtf? anyways, not the other way around, you figure out that it's grams in functions of moles, in other words, g/mol, and so all you have to do is mass/moles, etc It's actually good to know that a Watt is actually a J/s, you know, that kind of stuff, once you get the hang of that you'll be able to slack off and not learn all this crap by heart Although it probably doesn't affect you guys as much... There's no end of year exams from what I could gather :/ Oh yeah and isn't that 6*10^23 usually referred to as Avogadro's number? (NA) |
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Toxic in a sublime state of mind Level: 75 Posts: 2025/2857 EXP: 3732709 For next: 94195 Since: 03-15-04 Since last post: 3 days Last activity: 8 hours |
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god, do I NOT envy you. I hope your teacher was cooler than mine. Hell I KNOW that he/she is, because I have horror/comedy stories about my chem teacher that make me shudder. |
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Colleen Administrator Level: 136 Posts: 4550/11302 EXP: 29369328 For next: 727587 Since: 03-15-04 From: LaSalle, Quebec, Canada Since last post: 3 hours Last activity: 1 hour |
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Ugh... don't remind me about chemistry. I could muddle through the formulas (that I can't remember now) all right but I was clueless in the lab. The teacher was OK but it was still bleh. Problem was I was forced (since I was in the IB program) to take Chem or Physics. |
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NSNick Laidback Admin Level: 85 Posts: 1219/3875 EXP: 5895841 For next: 2699 Since: 03-15-04 From: North Side School: OSU Since last post: 9 hours Last activity: 1 hour |
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Originally posted by kiwibongaYeah. I think it's somewhere along the line of 6.04 x 1023 |
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Prier Archangel Administrative Priestess. NUCLEAR SUB WEEEOOOO Level: 119 Posts: 3573/8392 EXP: 18790939 For next: 138352 Since: 03-15-04 From: Nerima Dist. - Tokyo, Japan Since last post: 1 day Last activity: 1 day |
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What's the one where you have to know Carbon-12 as a constant and then the weight of each element to figure out a formula...is that molecular mass? I think I mixed that up with this one (the easier one) when I was trying to remember how to do Chemistry from four years ago for Ash. :\ | |||
Heian-794 Red Super Koopa Level: 44 Posts: 485/896 EXP: 611014 For next: 271 Since: 06-01-04 From: Kyoto, Japan Since last post: 21 days Last activity: 10 days |
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Originally posted by NSNickOriginally posted by kiwibongaYeah. I think it's somewhere along the line of 6.04 x 1023 6.02 x 1023 if I recall correctly, though 6 is a good enough approximatoin. BTW, Arwon, your first line of advice: A mole is just a particular number. Like "a dozen" is 12, "a thousand" is 1000... "a mole" is 6x10^23. ...is what carried me through that part of chemistry. The concept of a "mole" was prety confusing until I started thinking about it this way. |
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Super Sion You BlockHead! Level: 70 Posts: 1564/2472 EXP: 3002513 For next: 13298 Since: 03-15-04 From: Yo Mommas House Since last post: 29 min. Last activity: 5 min. |
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At first I had no idea what I was doing with Moles...then my teacher made a recipe analogy and it all clicked...after that I understood it perfectly, but from that point on everything just got more complex. |
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