Preparation of salts: the decision chart
Which method you use to make a salt depends on one thing: whether the salt is soluble, and if so whether the other reactant is. Get the solubility right and the method — titration, react-and-filter, or precipitation — follows automatically.
Key facts
| Topic | Acid-Base Chemistry |
| Step 1 | is the salt soluble? |
| Soluble + soluble base | titration |
| Insoluble salt | precipitation |
Start with solubility
Recall the solubility rules: all nitrates and most chlorides and sulfates are soluble; most carbonates and many hydroxides are insoluble. Knowing whether your target salt is soluble — and whether the base you'd react with the acid is soluble — decides the method before you touch any apparatus.
Soluble salt from a soluble base (titration)
If both the salt and the alkali are soluble, you can't simply add excess and filter (nothing to filter off). Instead use titration: find the exact volume of acid that neutralises a measured volume of alkali (using an indicator), then repeat without indicator, and crystallise the pure salt from the resulting solution.
Soluble salt from an insoluble reactant (excess and filter)
If the salt is soluble but you react the acid with an insoluble base, metal or carbonate, add the solid in excess until no more reacts, then filter off the leftover solid. Evaporate and crystallise the filtrate to get the salt. The excess solid guarantees all the acid is used up.
Insoluble salt (precipitation)
If the salt itself is insoluble, mix two soluble solutions that contain the right ions; the salt drops out as a precipitate. Filter, wash and dry it. This is the method for salts like barium sulfate or silver chloride.
Frequently asked questions
How do I choose a method to prepare a salt?
Decide from solubility: insoluble salt → precipitation; soluble salt from a soluble base → titration; soluble salt from an insoluble base/metal/carbonate → add excess and filter.
Why use titration for a soluble base?
Because both reactants are soluble, there's no leftover solid to filter off — so you measure the exact neutralising volume with an indicator, then crystallise.
What does 'add in excess and filter' achieve?
Adding the insoluble solid in excess ensures all the acid reacts; filtering then removes the unreacted solid, leaving a pure salt solution.
How do you make an insoluble salt?
By precipitation — mixing two soluble solutions containing the required ions so the insoluble salt forms as a solid you can filter, wash and dry.
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