STPM Chemistry Form 6 Notes – Heterogeneous Ionic Equilibrium (Part 5)

by BerryBerryTeacher

in Berry Reference (Notes)

Solubility experiments or experiments involving saturated solution are important, as they allow the empirical value of molar solubility of a salt to be determined. This post from Berry Berry Easy, Part 5 on Heterogeneous Ionic Equilibrium for STPM Chemistry will be on the basics of solubility experiments, their methods and some pointers on predicting precipitation. Make sure you have read all the previous parts in this series of notes before continuing on.

[Tips: Try understanding the principles behind the formation of precipitation in terms of ionic product and solubility product. when you define them, throw in also words like saturated/unsaturated and precipitation occur/did not occur.]

STPM Chemistry Form 6 Notes – Heterogeneous Ionic Equilibrium (Part 5)

Heterogeneous Ionic Equilibrium Precipitation

Heterogeneous Ionic Equilibrium Precipitation

Solubility Experiments

  • Molar solubility of a salt is an empirical value and it can be determined from experiments involving saturated solutions.


  • Spectroscopy – the amount of absorbed light at a fixed wavelength depends on the concentration of ions. This method works only if one of the ions absorbs electromagnetic radiation.
  • Measuring the amount of salt added and then collecting, drying, weighing, and then subtracting the mass of precipitate from this value. This method works only if the salt is highly soluble.
  • An ion exchange column to exchange the cation in solution for hydronium. The concentration of hydronium ion determined via pH. This method works only if the salt does not exhibit acid-base properties and has a cation concentration of at least 10-5 mol dm-3.

Predicting Precipitation

  • If Q (ionic product) = Ksp, the solution is just saturated with ions and is at the point of precipitation.
  • If Q < Ksp, the solution is unsaturated and precipitation cannot occur.
  • If Q > Ksp, precipitation occur.

This ends of the Part 5 notes on the topic of Heterogeneous Ionic Equilibrium for STPM Form 6 Chemistry students from Berry Berry Easy. In Part 6, Berry Readers will get to study the effects of common ion effect which occur when two substances which give the same ion when ionised are involved in a chemical equilibrium. Interesting situation, so do return to the site for more berry goodness.

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