How to decide when to use this method?
Examples:
- acid + metal → salt + hydrogen gas
- acid + insoluble base → salt + water
- acid + insoluble carbonate → salt + water +carbon dixoide
Step by Step for Adding to Excess Method
Objective: Prepare Zinc Sulfate (ZnSO₄)
Step 1:
- Use the solubility table to determine whether the salt is soluble in water.
- Zinc Sulfate is soluble in water
Step 2:
- Identify the starting materials for adding to excess method
Step 3:
- Select the starting materials for adding to excess method
- Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
Step 4: Prepare the Salt
- Add the Zn powder to the acid little by little, until no more reaction takes place. (No more effervescence)
- There will be some solid remaining behind. To remove this excess solid, filtration is performed. Collect the filtrate, this is zinc sulfate solution.
- Heat the filtrate in an evaporating dish.
- Stop the heating until one-third of the solution remains to get a saturated solution.
- Leave the saturated solution to cool and for crystallization to take place.
- Filter to collect the crystals formed. Wash with distilled water and dry the crystals with filter paper.
