The general concept of ionic equilibrium revolves around the tendency of acid to donate a proton to other substances and base to accept a proton to other substance, or simply acid being a proton donor and base being a proton acceptor. This brings us to Part 1 in the long series of notes on Ionic Equilibrium for STPM Chemistry Form 6 (Kimia Tingkatan 6) from Berry Berry Easy.
In this part, you’ll learn the terms and concepts involving the Brønsted-Lowry Acid-Base Theory, Strong and Weak Acids and Bases (limited to common strong acids and common strong bases).
(Tips: Do focus on the types of bases and acids use and the calculations involved.)
STPM Chemistry Form 6 Notes – Ionic Equilibrium (Part 1)
Natural Universal Indicator_Purple cabbage
The Brønsted-Lowry Acid-Base Theory
An acid is a proton (H+) donor
A base is a proton (H+) acceptor
Strong and Weak Acids and Bases
- Strength (strong or weak) – amount of ionisation / dissociation of a particular acid or base.
- Concentration – amount of acid or base
I) Common strong acids
- hydrochloric acid (HCl)
- hydrobromic acid (HBr)
- hydroiodic acid (HI)
- nitric acid (HNO3)
- perchloric acid (HClO4)
- sulphuric acid (H2SO4)
Example: Hydrogen chloride gas dissociate (break) completely in water.
HCl + H2O –> Cl- + H3O+
- H3O+ ion is hydronium ion
- All the HCl ionises completely (≈ 100%) to H3O+ and Cl-
- HCl is a strong acid
- Water acts as a base by accepting the proton from the hydrogen chloride
Calculating ion concentration in solution
Example: Initial concentration of HCl 0.15 mol dm-3 = 0.15 moles of HCl gas bubble into a 1 dm3 of water.
[HCl] = 0.15 because HCl ionises completely in water.
[H3O+] = 0.15 and [Cl-] = 0.15
II) Common strong bases
- sodium hydroxide (NaOH)
- potassium hydroxide (KOH)
- barium hydroxide (Ba(OH)2)
- Caesium hydroxide (CsOH)
- Strontium hydroxide (Sr(OH)2)
- Calcium hydroxide (Ca(OH)2)
- Lithium hydroxide (LiOH)
Example: Sodium hydroxide (a salt) dissociates (break) completely in water.
NaOH –> Na+ + OH-
- All the NaOH dissociates completely (≈ 100%) to Na+ + OH-
- NaOH is a strong base
- Water acts as a acid by donating the proton to sodium hydroxide
Calculating ion concentration in solution
Example: Initial concentration of NaOH 0.25 mol dm-3 = 0.25 moles of NaOH into a 1 dm3 of water.
[NaOH] = 0.25 because NaOH ionises completely in water.
[Na+] = 0.25 and [OH-] = 0.25
In Part 2 of this series (next part), you’ll learn about the same sub-topic but with focus on common weak acids and common weak bases.
