pH-salts - Predicting Predicting thepHof saltsolutions...

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Predicting  Predicting  the pH     of  the pH     of  salt solutions salt solutions
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Hydrolysis of ions Hydrolysis of ions Hydrolysis refers to a reaction with water (e.g. splitting water into H + and OH ) When salts are added to water, pH can change E.g. when Na 3 PO 4 is added to water, ions form Na 3 PO 4 (aq) 3Na + (aq) + PO 4 3– (aq) These ions may react with H 2 O, affecting the pH PO 4 3– (aq) + H + (aq) HPO 4 2 (aq) Na + (aq) + OH (aq) NaOH (aq) If the anion (-ve) reacts to remove lots of H + but the cation (+ve) removes very little OH , then H + will decrease and the solution will be basic.
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The degree of hydrolysis The degree of hydrolysis PO 4 3– (aq) + H + (aq) HPO 4 2 (aq) Na + + OH NaOH The problem with writing equilibria this way is we do not know the strength of the reactions However, if we reverse the reaction we can look up Ka and Kb values (pg. 608, 615): HPO 4 2 PO 4 3– + H + NaOH Na
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pH-salts - Predicting Predicting thepHof saltsolutions...

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