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mol, g.mol and g.mol-1

Posted: Mon Sep 30, 2019 9:13 pm
by Baoying Li 1B
Hello! I am confused about the units mol, g.mol and g.mol-1. They appear often in the textbook. Are they interchangeable? What's the difference?

Re: mol, g.mol and g.mol-1

Posted: Mon Sep 30, 2019 9:17 pm
by Jessica Tran_3K
Hi,

g.mol-1 is grams per mol, so it is not interchangeable with the unit mol. I am not quite sure about g.mol either.

Re: mol, g.mol and g.mol-1

Posted: Mon Sep 30, 2019 9:20 pm
by Rebecca Epner 4A
These are all different units. I actually don't quite understand the difference between g.mol and g.mol-1 (so far I think we've only used g.mol-1). Mol=moles as in the number of atoms in exactly 12g of carbon-12 (6.022 x 10^23 units of whatever you're measuring). g.mol-1 is the notation for grams per mol.

Re: mol, g.mol and g.mol-1

Posted: Mon Sep 30, 2019 9:42 pm
by Annie Chantasirivisal_4G
g.mol and g.mol-1 are not interchangeable, as the -1 in g.mol-1 is supposed to represent the mol being brought up as a numerator when it is originally a denominator, meaning it's g times mol-1.
g.mol-1 can also be also written as g/mol, though I'm assuming there is a preference of g.mol-1 for this class as it's easier to use when it's not in fraction format.

I've yet to see just g.mol in my chemistry career, so I'm not sure what it is either, but I hope the explanation for g.mol-1 is understandable.

Re: mol, g.mol and g.mol-1

Posted: Mon Sep 30, 2019 10:58 pm
by Justin Seok 2A
Just to add some context to g.mol-1, g.mol-1 is usually used as a unit for molecular weight/molar mass, which is the mass of a sample, usually in grams, divided by the amount of substance of the sample. For example, a mole of oxygen would weight 15.999 grams, so the molar mass would be 15.99 g.mol-1.

Re: mol, g.mol and g.mol-1

Posted: Mon Sep 30, 2019 11:45 pm
by Jocelyn Thorp 1A
g*mol-1 is a weird notation, it can be more simply read as g/mol grams PER mole (since taking a negative exponent means multiplying by the reciprocal). I'm not 100% sure why this is the notation is used, maybe to fit everything in one line.

Re: mol, g.mol and g.mol-1

Posted: Mon Sep 30, 2019 11:52 pm
by Jesse H 2L
g.mol-1 is interchangeable with g/mol, the exponent -1 denoting the fraction

Re: mol, g.mol and g.mol-1

Posted: Wed Oct 02, 2019 11:36 am
by Helen Struble 2F
Mols are not the same as g*mol or g*mol-1. A mole is a unit of amount—in chemistry, it is usually used to represent how many particles are in a certain mass of compound (this is much easier than doing calculations using the actual number of atoms/particles). If you need to know exactly how many atoms are in a mass of a substance, use Avagadro's number to convert, knowing that there are 6.022 * 10^23 atoms in one mole of any substance.

G*mol-1 is equivalent to g/mol. g*mol-1 and g/mol are used to denote molar masses. Molar masses can be used as a conversion factor to convert between grams and mols of a compound. I usually find in calculations it is easier to use the fractional notation (g/mol) because then it is easier to make sure conversion factors are cancelling correctly. In my head at least, it is much easier to follow 1.0 mol oxygen * 16.0 g/mol = 16. g oxygen than 1.0 mol oxygen * 16.0 g*mol-1 = 16. g oxygen.

Keep in mind, you can inverse conversion factors to work a problem backwards. By using the inverse of molar mass, we can convert from grams to mols. For example, 16.0 g oxygen * 1.0 mol/16.0 g = 1.0 mol oxygen. 1 mol/16.0g is simply the inverse of oxygen's molar mass, 16.0g/mol. This works because the units are still cancelling appropriately.

Re: mol, g.mol and g.mol-1

Posted: Wed Oct 02, 2019 12:25 pm
by Brandon Valafar
I have not seen g.mol yet. However mol and g.mol-1 CANNOT be used interchangeably. They mean completely different things. Mol is the unit for moles. For example if a problem said 8.13 mol NaCl, it would mean that there are 8.13 Moles of NaCl. On the other hand, g.mol-1 means grams PER mole. The negative exponent provides a fraction where grams are in the numerator and moles are in the denominator, but it's just easier to write this way.

Re: mol, g.mol and g.mol-1

Posted: Thu Oct 03, 2019 10:19 am
by Erik Buetow 1F
mol are different than g.mol and g.mol-1, but I'm not totally sure what the difference is between g.mol and g.mol-1.

Re: mol, g.mol and g.mol-1

Posted: Thu Oct 03, 2019 10:37 am
by Kyle Harvey 4F
g.mol-1 is interchangeable or equivalent to g/mol or grams per mol. In addition, (and someone correct me if I am wrong) I am pretty sure g.mol is representative of grams multiplied by moles, but I am not sure of a situation or problem where that would be used.

Re: mol, g.mol and g.mol-1

Posted: Thu Oct 03, 2019 7:01 pm
by Areli C 1L
From what I've seen so far, grams/mole is equal to g.mol-1. Lavelle prefers us to write it as the latter since it makes canceling units simpler. I haven't seen g.mols though, so I wouldn't be able to explain the difference.

Re: mol, g.mol and g.mol-1

Posted: Thu Oct 03, 2019 8:50 pm
by Tahlia Mullins
I find it easier to write out g/mol when performing calculations instead of using g.mol-1. Just a tip to make things easier to follow when there may be some heavy stoichiometry!