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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: angstridd3n on July 11, 2009, 10:51:59 AM

Title: pH after a reaction
Post by: angstridd3n 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. :)
Title: Re: pH after a reaction
Post by: Borek on July 11, 2009, 11:45:56 AM
There is no reaction (other, than HNO3 dissociation).
Title: Re: pH after a reaction
Post by: 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.
Title: Re: pH after a reaction
Post by: plankk on July 11, 2009, 01:57:52 PM
What is the pH scale?
Title: Re: pH after a reaction
Post by: angstridd3n 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...
Title: Re: pH after a reaction
Post by: Borek 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.
Title: Re: pH after a reaction
Post by: AWK 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
Title: Re: pH after a reaction
Post by: sjb 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?)
Title: Re: pH after a reaction
Post by: Borek 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.
Title: Re: pH after a reaction
Post by: sjb 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)
Title: Re: pH after a reaction
Post by: AWK 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