Using Solubility Rules to Predict Precipitate Formation during Double Displacement Reactions
Solubility – a measure of the amount of a substance (solute) that can dissolve in a quantity of water
(solvent) at a given temperature and pressure.
Ex. of a substance with a high solubility (quite a bit can dissolve) in a litre of water – NaCl
(s)
Ex. of a substance with a low solubility in a litre of water – Ca(OH)
2(s)
The solubility of different ionic compounds is summarized in the Solubility Table on Pg. 54 in the textbook. Double displacement reactions occur in aqueous (aq.) solution. The Solubility Table can be used to predict if an ionic compound produced during a double displacement reaction has a high solubility
-state is (aq.), or has a low solubility -state is (s).
Ex. 1 Write a balanced chemical equation to show the products and their state when aqueous solutions of potassium iodide and lead(II) nitrate are combined.
Ex. 2 Write a balanced chemical equation to show the products and their state when aqueous solutions of sodium sulphate and calcium chloride are combined.
Writing Total and Net Ionic Equations from Double Displacement Equations
Purpose : to show the ions that are the only ones involved in forming the precipitate in a Double
Displacement Reactions.
Steps to Follow :
1) Write the balanced chemical equation for the double displacement reaction, including the states of the chemicals;
2) Total Ionic Equation : re-write the chemical equation with all the ionic compounds that are highly soluble in water (aq.) separated into their respective ions. IF ANY SUBSTANCE IS NOT
IN (aq.) LEAVE THE FORMULA AS IT IS;
3) Net Ionic Equation : cancel out any identical ions that appear on both sides of the reactant and product sides of the Total Ionic Equation. What remains is the Net Ionic Equation, showing the ions involved in forming the precipitate.
Ex. Determine the Net Ionic Equation for the double displacement reaction between aqueous solutions of barium sulphide and sodium sulphate.