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Topic: pH after a reaction  (Read 7407 times)

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Offline angstridd3n

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pH after a reaction
« on: July 11, 2009, 10:51:59 AM »
Hey there!

I have been given the following exercise:

Calculate the pH of a solution that results from the mixture of 15.00ml HNO3 0.05 M, Ca(NO3)2 0.06 M and KCl 0.02 ml at 25ºC.

I have absolutely no idea how to write a balanced equation for this and I'm feeling quite lost since I have no idea how to calculate it.

Thanks in advance. :)
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Offline Borek

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Re: pH after a reaction
« Reply #1 on: July 11, 2009, 11:45:56 AM »
There is no reaction (other, than HNO3 dissociation).
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Offline angstridd3n

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Re: pH after a reaction
« Reply #2 on: July 11, 2009, 11:55:30 AM »
Then how do I calculate the pH of such a solution?
Even if I only work with the dissociation of HNO3 I don't understand what I have to do with the molarity and volume of the other substances.
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Offline plankk

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Re: pH after a reaction
« Reply #3 on: July 11, 2009, 01:57:52 PM »
What is the pH scale?
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Offline angstridd3n

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Re: pH after a reaction
« Reply #4 on: July 12, 2009, 05:26:08 AM »
What do you mean by that?
I think this is supposed to give a quite basic pH...
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Offline Borek

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Re: pH after a reaction
« Reply #5 on: July 12, 2009, 08:17:31 AM »
I suppose plankk meant 'what is pH definition'.

You are mixing acid and neutral salts - why do you expect it to be basic?

Other substances will change ionic strength of the solution. But first we have to deal with the pH in terms of concentration, not activity.
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Offline AWK

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Re: pH after a reaction
« Reply #6 on: July 13, 2009, 03:39:38 AM »
Quote from: angstridd3n on July 11, 2009, 11:55:30 AM
Then how do I calculate the pH of such a solution?
Even if I only work with the dissociation of HNO3 I don't understand what I have to do with the molarity and volume of the other substances.

Calculate of concentration of HNO3 after mixing
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Offline sjb

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Re: pH after a reaction
« Reply #7 on: July 13, 2009, 03:34:52 PM »
Quote from: AWK on July 13, 2009, 03:39:38 AM
Calculate of concentration of HNO3 after mixing

Which would be fine, if we had a volume of calcium nitrate, but we don't, so ...? (Or am I missing something?)
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Offline Borek

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Re: pH after a reaction
« Reply #8 on: July 13, 2009, 04:05:32 PM »
Isn't it a component present in 15 mL?

I am not sure, but that's how I read the question.
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Offline sjb

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Re: pH after a reaction
« Reply #9 on: July 13, 2009, 04:16:52 PM »
It's not how I read it . I read the recipe as

* 15.00ml HNO3 0.05 M
* Ca(NO3)2 0.06 M and
* KCl 0.02 ml (also missing a concentration, perhaps, but may not be important).

Total volume 15.02ml plus a volume of Ca(NO3)2(aq) (unknown as yet)
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Offline AWK

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Re: pH after a reaction
« Reply #10 on: July 14, 2009, 05:31:53 AM »
Quote
Ca(NO3)2 0.06 M and KCl 0.02 ml at 25ºC.
yes, something is missing in this part. You need to know both volumes and concentrations
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