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Learn about the Brønsted-Lowry theory of acids and bases, proton transfer, conjugate acid-base pairs, and the strength of acids and bases. Understand the role of water as an amphoteric substance and discover acid-base indicators.
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H+ is transferred Note:We often say “Proton” Brønsted-Lowry theory of acids and bases H+ Cl- + NH3Cl- + NH4+ An acid is a H+ donor HCl A base is a H+ acceptor NH3
HCl + H2O H3O+(aq) + Cl- (aq) Oxonium Ion acids and bases in solution HCl H+(aq) + Cl- (aq)
NaOH Na+(aq) + OH- (aq) CO3 2- (aq) +H2O(l) HCO33-aq) + OH-(aq) Alkalis vs bases A base is a H+ acceptor An alkali is a base that dissolves in water to form hydroxide ions. All alkalis are bases; not all bases are alkalis!
Questions: Chemical Ideas page 194 Question 2 d,g,h & 3 b,c (extension: complete remaining parts of 2 &3)
HA(aq) H+(aq) + A- (aq) Conjugate acid Conjugate base Acid-base pairs An acid exists in solution in equilibrium: Overall we call this a conjugate acid-base pair
H2O(aq) H+(aq) + OH- (aq) H3O+(aq) H+(aq) + H2O(aq) Acid-base pairs Water can act as an acid OR a base: Proton donor Proton acceptor We say water is amphoteric
Questions: Chemical Ideas page 194 Question 4b & 5b (extension: complete remaining parts of 4 & 5)
HCl(aq) H+(aq) + Cl- (aq) C2H5OH (aq) H+(aq) + C2H5O -(aq) Strength of acids and bases A strong acid donates protons easily. A weak acid donates protons less easily, however the conjugate base accepts protons more easily than a strong acid
HIn(aq) H+(aq) + In-(aq) base When you add an acid Acid-base Indicators Acid base indicators are coloured organic substances that are weak acids. For example: Litmus acid
HIn(aq) H+(aq) + In-(aq) base When you add a base: HIn(aq) + OH- H2O(l) + In-(aq) Acid-base Indicators Acid base indicators are coloured organic substances that are weak acids. For example: Litmus acid