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Topic: Mass% and average molecular weight  (Read 980 times)

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Offline Jaime7078

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Mass% and average molecular weight
« on: September 22, 2024, 01:45:18 PM »
the density of 2 m sulfuric acid solution is 1.12 kg per liter. what is the total molar concentration of the solution? what is the average molecular weight? what is the mass fraction of oxygen?

Offline Borek

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Re: Mass% and average molecular weight
« Reply #1 on: September 22, 2024, 03:13:35 PM »
Please read the forum rules. You have to show your attempts at answering the question to receive help.
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Offline Jaime7078

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Re: Mass% and average molecular weight
« Reply #2 on: September 22, 2024, 06:07:49 PM »
molar concentration: 2M
average molecular weight:total mass = 1120g, mass of sulphuric acid = 2 mol × 98 g/mol = 196 g = 0.196 kg, Mass of water: 1.12 kg - 0.196 kg = 0.924 kg, Moles of water: 924 g / 18 g/mol = 51.33 mol, Total moles: 2 mol + 51.33 mol = 53.33 mol,Average molecular weight: 1120 g / 53.33 mol ≈ 21 g/mol.
mass fraction of oxygen: oxygen in water=821.33 g oxygen in h2s04=128 g, mass fraction = 84.7%

the thing is I dont if I should include water in my calculations because it doesn't specify that the solution is aqueous. I thinking I should have used that average molecular weight = density/concnetration or something

Offline Borek

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Re: Mass% and average molecular weight
« Reply #3 on: September 23, 2024, 04:01:59 AM »
the thing is I dont if I should include water in my calculations because it doesn't specify that the solution is aqueous. I thinking I should have used that average molecular weight = density/concnetration or something

Good catch, but if nothing else is given, assuming water solution is reasonable, this is the most common case.

Besides, 1.12 kg/L for 2M fits water solution.
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