STPM Chemistry Form 6 Notes – Ionic Equilibrium (Part 1)

by BerryBerryTeacher

in Berry Reference (Notes)

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

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.

Previous post:

Next post: