STPM Chemistry Form 6 Notes – Ionic Equilibrium (Part 3)

by BerryBerryTeacher

in Berry Reference (Notes)

Three Theories for Chemistry: Arrhenius Theory, Brønsted-Lowry Acid-Base Theory, Lewis Theory will keep us company in Part 3 of Ionic Equilibrium for STPM Chemistry Form 6 (Kimia Tingkatan 6) from Berry Berry Easy. In the first two parts, you were introduced to ‘common strong and weak acids and bases’ and also the Ostwald Dilution Law. While those weren’t difficult, this part would definitely be a challenge to all Berry Readers.

(Tips: Try to write down all three theories on a separate piece of paper a few times and see if you can fully distinguish the difference and state the main characteristics of the theories. You can only consider yourself to understand this part if you can differentiate all three theories off your head. This is a very important subtopic in the entire chapter.)

STPM Chemistry Form 6 Notes – Ionic Equilibrium (Part 3)

 

Natural Universal Indicator_Purple cabbage

Natural Universal Indicator_Purple cabbage

 

Arrhenius Theory: Svante Arrhenius (1884), Sweden

  • An Arrhenius acid is substances dissociate in water to produce H+ ions
  • An Arrhenius base is substances dissociate in water to produce OH- ions

Example:

HCl(aq) –> H+(aq) + Cl-(aq)
CH3COOH(aq) <—-> CH3COO-(aq) + H+(aq)

  • HCl and CH3COOH are Arrhenius acids

Example:

NaOH(aq) –> Na+(aq) + OH-(aq)
Ba(OH)2(aq) –> Ba2+(aq) + 2OH-(aq)

  • NaOH and Ba(OH)2 are Arrhenius bases

Limitation: Many compound show basic properties but do not contain OH-

Example: NH3, Na2CO3 and C2H5ONa

 

The Brønsted-Lowry Acid-Base Theory: Johannes Brønsted (1879-1947), Denmark and Thomas Lowry (1874-1936), England

  • A Brønsted-Lowry acid is a proton (H+) donor
  • A Brønsted-Lowry base is a proton (H+) acceptor
  • In an acid-base reaction, a proton is transferred from an acid to a base

Brønsted-Lowry acid-base reaction:

HB(aq) + A-(aq) <—-> HA(aq) + B-(aq)

  • HB and HA act as Brønsted-Lowry acid
  • A- and B- act as Brønsted-Lowry base

Conjugate base is the species formed when a proton is removed from an acid

Conjugate acid is the species formed when a proton is added to a base

  • B- is the conjugate base of HB
  • HA is the conjugate acid of A-

Conjugate acid-base pair differs only in the presence or absence of a proton, H+

Example:

Conjugate acid Conjugate base
NH4+ NH3
HSO4- SO42-
HF F-

Amphiprotic is a species that can either accept or donate a proton.

Example: H2O molecule

Hydronium ion (H3O+) – H2O molecule gain a proton
Hydroxide ion (OH-) – H2O molecule lose a proton

 

Lewis Theory: G.N. Lewis (1938), America

  • A Lewis acid is a species (an atom, ion or molecule) form a dative covalent bond by accepting an electron-pair from base
  • A Lewis base is a species form a dative covalent bond by donating an unshared electron-pair with an atom, ion or molecule

Example 1:

B(OH)3(aq) + H2O(l) <—-> B(OH)4-(aq) + H+(aq)

  • Lewis acid: Boric acid (H3BO3)
  • Lewis base: Water (H2O)

Example 2:

BF3 + NH3 –> BF3•NH3

  • Lewis acid: BF3
  • Lewis base: NH3

Example 3:

Cu2+(aq) + 4NH3(aq) –> [Cu(NH3)4]2+(aq)

  • Lewis acid: Cu2+
  • Lewis base: NH3

Example 4:

Ni(s) + 4CO(g) <—-> Ni(CO)4(l)

  • Lewis acid: Ni
  • Lewis base: CO

This is the end of Part 3. The next Part (4) will be relatively easy as compared to this part but still tricky. So be prepared to learn water-based acid-base chemistry, acid dissociation, base hydrolysis and a summary of the three concepts in Part 4 of Berry Berry Easy’s STPM Chemistry notes on Ionic Equilibrium. It is is not essential, it ain’t another quality study note from Berry Berry Easy.

Previous post:

Next post: