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pH of Salts

pH of Salts. HSC Chemistry – Acidic Environment R Slider. The pH of a salt depends upon the relative strength of the ions that make up the salt Very few salts are neutral Salts completely dissociate into their ions when sufficiently dilute NaCl (s)  Na + ( aq ) + Cl - ( aq )

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pH of Salts

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  1. pH of Salts HSC Chemistry – Acidic Environment R Slider

  2. The pH of a salt depends upon the relative strength of the ions that make up the salt • Very few salts are neutral • Salts completely dissociate into their ions when sufficiently dilute NaCl(s) Na+(aq) + Cl-(aq) • It is possible for these ions to interact with water to produce H+ or OH- ions which results in acidic or alkaline solutions. These are known as hydrolysis reactions All salts are not neutral

  3. Neutral anions are formed from strong acids • Neutral cations are formed from strong bases • NaCl is a neutral salt because the ions that are formed derive from a strong acid and base • HCl + NaOH NaCl + H2O • Both of the acid and base completely dissociate, so there is no tendency for these ions to undergo hydrolysis reactions. Neutral ions

  4. These react with water to form hydroxide ions • H2CO3 + 2NaOH  Na2CO3 + H2O • Na2CO3  2Na+ + CO32- • CO32- + H2O  HCO3- + OH- In the above reactions: • NaOH is a strong base so the Na+ will not react with water to form hydrogen ions • Carbonic acid is weak, so the carbonate ion will react with water to a small extent to form OH- ions Basic anions are formed by weak acids Basic ions (anions only)

  5. Acidic anions are formed from polyprotic acids • In order to be acidic, a salt anion must contain a donatable proton (H+) HSO4- + H20  H3O+ + SO42- Note: not all polyprotic acid anions are acidic. HCO3- and HPO42- are basic Acidic ions (anions)

  6. Acidic cations are formed by weak bases • Again, a donatable hydrogen must be available on the cation. NH4+ + H2O  NH3 + H3O+ The ammonium ion comes from the weak base, ammonia, so a hydrolysis reaction can occur to a small extent producing hydronium ions. Acidic ions (cations)

  7. Neutral anions are formed from strong acids • Neutral cationsare formed from strong bases • Basic anions are formed from weak acids • Acidic anions are formed from polyprotic acids • Acidic cationsare formed from weak bases Summary

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