pH-salts-handout - Predicting Predicting the pH of salt...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Predicting Predicting the pH the pH of salt of salt solutions solutions 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. 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 + + OH Ka= 4.5 x 10 13
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.
Ask a homework question - tutors are online