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#1 2013-05-30 02:35:21

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 16,621
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potenz Hydrogen

Calculate the pH of of 0.002 m of H[sub]2[/sub]SO[sub]4[/sub]

I do not even understand what m means


'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Humanity is still kept intact. It remains within.' -Alokananda

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#2 2013-05-30 02:35:59

bobbym
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From: Bumpkinland
Registered: 2009-04-12
Posts: 86,228

Re: potenz Hydrogen

It means molar does it not?


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#3 2013-05-30 03:58:12

bob bundy
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Registered: 2010-06-20
Posts: 6,376

Re: potenz Hydrogen

hi Agnishom,

Answer from Mrs B:

0.002m means the concentration of H2SO4 in moles per cubic decimetre.

It's a strong acid so it is fully dissociated in water => the concentration of hydrogen ions is 0.002 x 2 = 0.004 (as it's H2.....)

The pH is then given by

Hope that helps, smile

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#4 2013-05-30 17:10:40

barbie19022002
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Registered: 2013-05-24
Posts: 1,314

Re: potenz Hydrogen

H2SO4 means sulphuric acid...right..


Jake is Alice's father, Jake is the ________ of Alice's father?
Why is T called island letter?
think, think, think and don't get up with a solution...

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#5 2013-05-30 17:36:46

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 16,621
Website

Re: potenz Hydrogen

Yes, thats sulphuric acid.

Bob, does hydrogen concentration equal to that m number times the number of molecules of H
If that is so, I wanted to post another problem


'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Humanity is still kept intact. It remains within.' -Alokananda

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#6 2013-05-30 17:47:32

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,518

Re: potenz Hydrogen

Hi Agbishom

It seems to be so.


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#7 2013-05-30 18:27:03

bob bundy
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Registered: 2010-06-20
Posts: 6,376

Re: potenz Hydrogen

hi Agnishom

does hydrogen concentration equal to that m number times the number of molecules of H

Yes, it does.  Post your problem.

A cautionary tale:

There once was a student from Lahore,
Said: "I need a drink,  that's for sure",
His error was a blow,
What he thought was H2O,
Was actually H2SO4.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#8 2013-05-30 18:57:15

Agnishom
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From: The Complex Plane
Registered: 2011-01-29
Posts: 16,621
Website

Re: potenz Hydrogen

Calculate the pH of a solution which consists of 0.01 m of KOH and 0.02 of HNO[sub]3[/sub]


'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Humanity is still kept intact. It remains within.' -Alokananda

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#9 2013-05-30 18:57:41

barbie19022002
Member
Registered: 2013-05-24
Posts: 1,314

Re: potenz Hydrogen

Oh my god...he though sulphuric acid was water...very funny..


Jake is Alice's father, Jake is the ________ of Alice's father?
Why is T called island letter?
think, think, think and don't get up with a solution...

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#10 2013-05-30 19:29:55

Agnishom
Real Member
From: The Complex Plane
Registered: 2011-01-29
Posts: 16,621
Website

Re: potenz Hydrogen

Why did he think so?


'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Humanity is still kept intact. It remains within.' -Alokananda

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#11 2013-05-30 19:43:57

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,376

Re: potenz Hydrogen

Why did he think so?

Both colourless liquids.  Always read the label!

Calculate the pH of a solution which consists of 0.01 m of KOH and 0.02 of HNO3

These two react and there may be some acid or alkali left at the end to give a pH.  But without knowing the amount of each in the solution you cannot figure that out.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#12 2013-05-30 19:49:17

Agnishom
Real Member
From: The Complex Plane
Registered: 2011-01-29
Posts: 16,621
Website

Re: potenz Hydrogen

that's a point. I will try to look for the exact question


'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
'Humanity is still kept intact. It remains within.' -Alokananda

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#13 2013-05-31 06:33:51

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,376

Re: potenz Hydrogen

I have consulted with my resident chemist.  The problem is far from straight forward even when you know the two volumes.

For simplicity, let's say there are equal amounts of each.

The 0.01 and 0.02 mean that both are dissolved in water to give those concentrations.  If equal amounts are mixed together they will react.  One molecule of KOH with react with one molecule of HNO3 to give KNO3 and H2O.  So now there is extra water.

Only half the acid will react because of the different concentrations.  The remaining acid is now much more dilute (i) because of the water the alkali was dissolved in and (ii) because of the water generated by the reaction.  I'm still waiting for a response about what the concentration now is.  eg.  If there was 100 ccs of acid and 100 ccs of alkali, then that's 200 ccs due to (i) and what? due to (ii).

LATER EDIT:

The oracle says ignore (ii).  Cannot establish whether that's because it is negligible or because of some strange molar argument but anyway that makes life simpler.

We then have 0.02 becomes 0.01 because of the reaction, and then 0.005 because of (i).

So the answer would be -log(0.005).

eek

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#14 2013-05-31 08:57:30

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,518

Re: potenz Hydrogen

Hi Bob

I love the poem, but I find this versuon better:
"Little John was very thirsty,
Now he is no more,
For what he thought was H2O
Was H2SO4"

I think it gets worse if we change 'thought' to 'taught'.


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#15 2013-05-31 09:17:00

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 86,228

Re: potenz Hydrogen


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#16 2013-05-31 19:12:04

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,376

Re: potenz Hydrogen

Thanks Stefy,

That's the poem I was trying to remember.  But I thought it was a limerick.  I made that one up myself.  I'll abandon poetry and stick to maths in future.  smile

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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