October 17, 2019, 02:59:57 PM
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Topic: How can I find the pH of this salt?  (Read 172 times)

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Online INeedSerotonin

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How can I find the pH of this salt?
« on: October 11, 2019, 06:47:11 PM »
One dissolves 100 g of (CH3CH2COO)2Ca in half a litre of distilled water. What is the pH of its aqueous solution?

I know that the molar mass is 186 g, so there are 100 / 186 moles = 0.53 moles in half a litre of water = 1.06 moles / litre

But I'm lost here. I know that pH is [H+], and I know that Ka = [Products] / [Reagents], but I don't know how to proceed.

The options are "acidic", "neuter" and "basic". Any hints?

Thanks

Offline AWK

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Re: How can I find the pH of this salt?
« Reply #1 on: October 12, 2019, 01:33:40 AM »
Have you ever heard of salt hydrolysis and how you decide about the pH of the solution in this case?
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Re: How can I find the pH of this salt?
« Reply #2 on: October 12, 2019, 09:43:26 AM »
Have you ever heard of salt hydrolysis and how you decide about the pH of the solution in this case?

I hadn't! But I did some research, and I think I've learnt it now.

So the salt is basic because the propionic acid is weak, and Ca(OH)2 is strong?

Offline chenbeier

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Re: How can I find the pH of this salt?
« Reply #3 on: October 12, 2019, 09:59:57 AM »
Yep.  You can say so.  Compare pkb and pks. Probably more to neutral as to alkaline. pH 7-8 I guess.

Offline AWK

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Re: How can I find the pH of this salt?
« Reply #4 on: October 12, 2019, 10:46:47 AM »
Rather closer to 9.5. But since a high ionic strength of the solution, pH cannot be calculated reliably. An error may be about 0.2 to 0.5 pH units.
When in equilibrium with CO2 from air one may expect pH about 1 unit lower.

2.12 M sodium acetate will also be a quite good approximation.

« Last Edit: October 12, 2019, 10:59:34 AM by AWK »
AWK

Online INeedSerotonin

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Re: How can I find the pH of this salt?
« Reply #5 on: October 12, 2019, 04:17:21 PM »
Thank you, guys!

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