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Chemistry: Moles?
I've been given a few different sets of questions to do with Avogadro's Constant, but I'm starting to confuse myself!
Could someone go through this question step-by-step so that I can understand what it is need to do?:
1. What is the mass in g of 2.5 mols of Lithium Sulphate?
Also, I can calculate the number of particles in a mol of an atom, but is what is the difference in calculating the number of particles in a mole of an ion?
I would be extremely grateful for any help! Thank you in advance :)
2 Answers
- 7 years agoFavorite Answer
Yes. So the way to go about these equations is by using dimensional analysis.
1) Find the amount of grams in ONE single mole of Lithium Sulphate
• Li (+1 charge) + SO4 (-2 charge) = Li2SO4
• Li (6.941) * 2 = 13.882
• SO4 = S (32.065) + O4 (15.999*4) = 96.0626
• Li2 + SO4 = 13.882 + 96.0626 = 109.9446g
----> So...1mol Li2SO4 = 109.9446g (or 109.9446g/mol LiSO4)
2) Use what we know: we have 2.5mol LiSO4
• So if we have 2.5mol and we know that 1mol = 109.9446g, then we can just multiply 109.9446g/mol by 2.5mol
• This will cancel 'mol' and leave us with 'g' along with the number we calculated
• So (2.5mol)(109.9446g/mol) = 274.8615g
3) Round to the correct number of sigfigs
• When doing this, always do the number of sigfigs for the smallest number used in the process, which is '2.5'
• 2.5 has 2 sigfigs, so if we round our answer to 2 sigfigs...
----> ...we get: 270g
- electron1Lv 77 years ago
Avogadro's Constant represents the number of particles that are in one mole of the substance. To determine the mass of a specific number of moles of a compound, multiply the number of moles by the mass of one mole of the compound.
Lithium sulfate is Li2SO4. The mass of one mole is 2 * 6.94 + 32.1 + 4 * 16 = 109.98 grams
Mass = 2.5 * 109.98 = 275.95 grams
Let’s determine the number of moles of lithium sulfate, by multiplying number of moles by Avogadro’s constant.
N = 2.5 * 6.02 * 10^23 = 1.505 * 10^24 moles
Since lithium sulfate contains two lithium ions, the number moles of this ion is 3.01 * 10^24. Since it contains one sulfate ion, the number moles of this ion is 1.505 * 10^24. If you still have questions, send them to the following email address.
morrison60957@yahoo.com
