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Old March 10th, 2006, 12:03
moni moni is offline
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Default Calculate the molecular mass

A 1.80g sample of acid H2X, required 14.00 ml of KOH solution for neutralization of all the hydrogen ions. Exactly 14.2 ml of this same KOH solution was found to neutralize 10.0 ml of 0.750 M H2SO4 .Calculate the molecular mass of H2X?
THANX FOR HELP
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Old March 10th, 2006, 17:27
arit arit is offline
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Could you show how far you've got yourself?

I think I atleast got the idea how you calculate the molecular mass, but I think I either made false assumptions or just miscalculated.
Things that bother me:
The acid being the form H2X, suggests that it's diprotic, but I assumed that it is monoprotic, as I didn't have Ka(HX-).
The answer I got is quite unbelieveable to me atleast
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Old March 10th, 2006, 18:05
moni moni is offline
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that is the problem i don't know where to start.
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Old March 10th, 2006, 19:21
arit arit is offline
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I started by calculating the concentrations of the KOH solution. You can get it from the reaction with H2SO4. By determining the amount of H30+ ions (in moles) in the H2SO4 solution you know how many moles (of KOH) the 14.2ml solution of KOH contains. (H2SO4 is a diprotic acid, H2SO4 -> HSO4-. HSO4- <-> SO4(2-) )

I'm not quite sure about this latter part, but here goes:

After you know the concentration and the volume of the KOH solution, you know how many moles it takes to neutralize the "unknown acid".
And this is where I probably did something wrong:
I assumed that the acid is a strong, monoprotic one. Otherwise I don't know how I would have calculated how many moles of acid there was in the solution.

Once you get how many moles of acid there was in the solution, you know
enough to calculate the molecular mass of it.
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Old March 10th, 2006, 19:28
moni moni is offline
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thank you so much for your help
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Old March 13th, 2006, 00:11
RobJim RobJim is offline
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Since the acid is described as H2X, I would assume it's a strong diprotic acid.
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