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Transcript of Water
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
Water
Water can behave as an acid or a base. Water contains H+ and OH- ions.
Water dissociates:H2O(l) H+
(aq) + OH-(aq)
Really H3O+ hydronium ion
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
Amphiprotic vs amphoteric
A substance that can donate or accept protons is called amphiprotic
Salts can act as acids and bases by donating or accepting H+ - usually H3O+ or OH- ions are formed – this is called amphoteric
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
acid base
HCl + H2O H3O+ + Cl-
Water is behaving as a base
donates proton
accepts proton
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
base acid
O2- + H2O OH-
Water is behaving as an acid
donates protonaccepts proton
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
Amphiprotic
Water is amphiprotic as it does not react with acids or bases to neutralise them – it does however donate or accept protons.
An amphoteric substance can neutralise an acid or a base
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
Acidic substancesWhen [H3O+] > [OH-] a solution is acidic An acidic substance is a substance that will either:
•dissolve in water to form an acidic solution OR
•Do not dissolve but react with bases and basic solutions
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
Basic substances
When [OH-] > [H3O+] a solution is basicA basic substance is a substance that will either:
• dissolve in water to form a basic solution OR
• Do not dissolve but react with acids and acidic solutions
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
Amphoteric substances
Amphoteric substances do not dissolve in water BUT do react with BOTH acidic and basic solutions.
Metal oxides and hydroxides are amphoteric
12 Chemistry 2.6 rxn rates, eqm, acids and bases CR 07
Al2O3 is amphoteric
Al2O3(s)+6H+(aq)2Al3+
(aq) +3H2O(aq)
Al2O3(s)+2OH-(aq)+3H2O 2Al(OH)4(aq)
+3H2O(aq)
evaporated NaAl(OH)4
Al2O3(s) has reacted with both an acidic solution and a basic solution