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Topic: why more H+ generated than expect?  (Read 4489 times)

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Offline feiz

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why more H+ generated than expect?
« on: November 04, 2007, 04:27:16 PM »
Someone show me like this in the pict.


My question is how H+ dissociated (1.77e-6) could more than H2CO3 (1.56e-8)


On the other hand, HCO3- is a weak base
But many people say its dissocation form is H+ CO3--, so it's acidic?
But I know that HCO3- could accept H+ more easily
so HCO3- is in fact base or acid??

If it's base, how to calculate the pH after adding 0.1M of HCO3- into pure water? (such as NaHCO3)


Thx a lot ^_^

Offline Borek

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Re: why more H+ generated than expect?
« Reply #1 on: November 04, 2007, 05:08:30 PM »
HCO3- is amphoteric, it can act as both acid and base.

Someone show me like this in the pict.

Whoever calculated it is a chemical idiot, ignore it and don't bother. Final result is an effect of using an equation outside if its range of application. You are right that the result is absurd.
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Offline feiz

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Re: why more H+ generated than expect?
« Reply #2 on: November 04, 2007, 08:40:13 PM »
HCO3- is amphoteric, it can act as both acid and base.

Could u pls show me an example in calculating pH of HCO3- as basic? ^_^

Quote
Whoever calculated it is a chemical idiot, ignore it and don't bother. Final result is an effect of using an equation outside if its range of application. You are right that the result is absurd.

Thx, my friends told me something similar to what you said, just wanna know more to support this kind of arguments though I know there is another K (~4.3e-7) can solve it and skip something ridiculous

Thx a lot :-)

Offline Borek

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Re: why more H+ generated than expect?
« Reply #3 on: November 05, 2007, 02:47:08 AM »
HCO3- is amphoteric, it can act as both acid and base.

Could u pls show me an example in calculating pH of HCO3- as basic?

That's not the way it works. You don't treat is as basic or acidic, but as both at the same time - and calculations are not easy. Luckily you may often use some simplications. See

http://www.chembuddy.com/?left=pH-calculation&right=pH-amphiprotic-salt
« Last Edit: November 05, 2007, 03:56:36 AM by Borek »
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Offline feiz

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Re: why more H+ generated than expect?
« Reply #4 on: November 05, 2007, 04:12:04 AM »
wow!! very great pointer!!!

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