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Solubility of salts
Carbonates: Sodium, potassium and ammonium carbonates are soluble. All other carbonates are insoluble.
Chlorides: All chlorides are soluble except for silver and lead chlorides are insoluble.
Nitrates: All nitrates are soluble.
Sulphates: All sulphates are soluble except for barium and lead sulphates are insoluble. Calcium sulphate is only slightly soluble.
All sodium, potassium and ammonium salts are soluble.
After identifying which types of salts are soluble and which types are not, we can then proceed to prepare a particular salt (be it a soluble or insoluble one) by selecting an appropriate method out of the different methods described below.
**Note that remembering solubility of salts is very very important. It not only help one to answer questions on this topic on preparation of salts, but also help one to be able to write the state symbols in chemical equations and also help in determining the identity of an unknown substance in the topic on qualitative analysis (both theory and practical papers).
Chlorides: All chlorides are soluble except for silver and lead chlorides are insoluble.
Nitrates: All nitrates are soluble.
Sulphates: All sulphates are soluble except for barium and lead sulphates are insoluble. Calcium sulphate is only slightly soluble.
All sodium, potassium and ammonium salts are soluble.
After identifying which types of salts are soluble and which types are not, we can then proceed to prepare a particular salt (be it a soluble or insoluble one) by selecting an appropriate method out of the different methods described below.
**Note that remembering solubility of salts is very very important. It not only help one to answer questions on this topic on preparation of salts, but also help one to be able to write the state symbols in chemical equations and also help in determining the identity of an unknown substance in the topic on qualitative analysis (both theory and practical papers).
How to prepare INSOLUBLE SALT (precipitation method)
1. Place a known volume of one soluble salt solution in a beaker .
2. Keep adding the other soluble salt solution and stir to mix until no more precipitate forms.
3. Filter out the precipitate.
4. The residue is the insoluble salt you are trying to get.
5. Wash residue with water.
6. Dry the insoluble salt crystals.
Watch the following video for an experiment on preparing insoluble salt by precipitation method.
2. Keep adding the other soluble salt solution and stir to mix until no more precipitate forms.
3. Filter out the precipitate.
4. The residue is the insoluble salt you are trying to get.
5. Wash residue with water.
6. Dry the insoluble salt crystals.
Watch the following video for an experiment on preparing insoluble salt by precipitation method.
How to prepare SOLUBLE SALT by titration method (using acid + alkali).
1. Place a known volume of acid (e.g. HCl) in a conical flask.
2. Add an indicator to the acid (if phenolphthalein is added, the colour will be colourless).
3. Add alkali (e.g. NaOH) from a burette until indictaor changes colour (phenolphthalein will change colour from colourless to pink). This is the end point of titration and neutralisation is completed.
4. Record volume of alkali used.
5. Repeat whole process again with the known volumes of acid and alkali to produce salt solution (but do not add indicator).
6. Heat salt solution by evaporation method to evaporate all water and obtain salt crystals. If salt is not heat stable, crystallisation method is used instead to obtain salt cystals.
7. Dry the salt cystals.
Watch the following video on a titration experiment to prepare sodium chloride (a soluble salt) from using hydrochloric acid (an acid) and sodium hydroxide (an alkali).
2. Add an indicator to the acid (if phenolphthalein is added, the colour will be colourless).
3. Add alkali (e.g. NaOH) from a burette until indictaor changes colour (phenolphthalein will change colour from colourless to pink). This is the end point of titration and neutralisation is completed.
4. Record volume of alkali used.
5. Repeat whole process again with the known volumes of acid and alkali to produce salt solution (but do not add indicator).
6. Heat salt solution by evaporation method to evaporate all water and obtain salt crystals. If salt is not heat stable, crystallisation method is used instead to obtain salt cystals.
7. Dry the salt cystals.
Watch the following video on a titration experiment to prepare sodium chloride (a soluble salt) from using hydrochloric acid (an acid) and sodium hydroxide (an alkali).
How to prepare SOLUBLE SALT using acid to react with excess metal/ insoluble metal oxide/ insoluble metal carbonate
1. Heat some acid in a beaker.
2. Keep adding metal/ insoluble metal oxide/ insoluble metal carbonate and stir at same time until excess metal/ metal oxide/ metal carbonate remains.
3. Filter mixture and throw away the residue which is the excess metal/ metal oxide/ metal carbonate.
4. Keep the filtrate which is the soluble salt solution.
5. Heat filtrate to evaporate most of the water until a saturated solution is formed by crystallisation.
6. Leave to cool and dry until salt crystals are formed.
7. Dry the salt crystals.
Acid + Metal → Soluble salt + Hydrogen
2HCl + Zn → ZnCl2 + H2
Acid + Insoluble metal oxide → Soluble salt + Water
2HCl + FeO → FeCl2 + H2O
Acid + Insoluble carbonate → Soluble salt + Carbon dioxide + Water
2HCl + ZnCO3 → ZnCl2 + CO2 + H2O
Watch the following video which focuses on the reaction acid with excess metal to prepare a soluble salt. Hydrogen gas is also given off in this reaction. **Take note that Group I very reactive metals (e.g. sodium and potassium) SHOULD NEVER BE USED in this reaction to prepare soluble salt as the reaction is highly explosive (check the video to understand the danger of this explosive reaction).
2. Keep adding metal/ insoluble metal oxide/ insoluble metal carbonate and stir at same time until excess metal/ metal oxide/ metal carbonate remains.
3. Filter mixture and throw away the residue which is the excess metal/ metal oxide/ metal carbonate.
4. Keep the filtrate which is the soluble salt solution.
5. Heat filtrate to evaporate most of the water until a saturated solution is formed by crystallisation.
6. Leave to cool and dry until salt crystals are formed.
7. Dry the salt crystals.
Acid + Metal → Soluble salt + Hydrogen
2HCl + Zn → ZnCl2 + H2
Acid + Insoluble metal oxide → Soluble salt + Water
2HCl + FeO → FeCl2 + H2O
Acid + Insoluble carbonate → Soluble salt + Carbon dioxide + Water
2HCl + ZnCO3 → ZnCl2 + CO2 + H2O
Watch the following video which focuses on the reaction acid with excess metal to prepare a soluble salt. Hydrogen gas is also given off in this reaction. **Take note that Group I very reactive metals (e.g. sodium and potassium) SHOULD NEVER BE USED in this reaction to prepare soluble salt as the reaction is highly explosive (check the video to understand the danger of this explosive reaction).
Watch the following video on reaction of acid (sulphuric acid) with insoluble metal carbonate (copper (II) carbonate) to prepare a SOLUBLE SALT (copper (II) sulphate). Carbon dioxide and water are also produced.
Acid + Insoluble carbonate → Soluble salt + Carbon dioxide + Water
Acid + Insoluble carbonate → Soluble salt + Carbon dioxide + Water