Salts Flashcards
Salts can exist in which forms at room temp?
- Dissolved
- aqueous solution - Solid crystals
- hydrated salt - Solid powder
- anhydrous salt
What is a salt?
Ionic compound which is formed when a metallic ion or an ammonium ion replaces one or more hydrogen ions in an acid.
How can we obtain an anhydrous salt?
Heating till dryness in an evaporating dish.
Which nitrates(NO3 -) are soluble?
ALL NITRATES ARE SOLUBLE.
Describe the solubility of halides? (Chlorides, iodides)
ALL SOLUBLE Except Lead(II) and silver.
Describe the solubility of sulfates. (SO4 2-)
ALL SOLUBLE except Calcium, barium and lead(II)
Describe the solubility of bases. (Hydroxides, oxides)
ALL INSOLUBLE except sodium, ammonium, calcium, potassium, barium.
Describe the solubility of carbonates. (CO3 2-)
ALL INSOLUBLE except sodium , ammonium, potassium.
What are hydrated salts?
Salts which combine with water to form aqueous solutions.
What happens when hydrated salts are heated gently?
They form anhydrous salts and water is given off.
When is titration used?
When salt is soluble, and it is either a sodium, ammonium or potassium salt.
Which salts are soluble?
Sodium, potassium and ammonium salts.
When is precipitation used?
For ALL INSOLUBLE SALTS.
Describe the precipitation process
- Mix the 2 solutions in beaker. Stir with glass rod. Precipitate of salt would have been formed.
- Filter out precipitate using funnel and filter paper.
- Wash residue by running distilled water through it.
- Allow salt to dry between sheets of filter paper.
When is reaction of an acid with an insoluble reactant used ?
- All soluble salts except SAP.
- Base, carbonate or metal must be insoluble(the cation)
- Copper and silver metal cannot be used.
Describe the process of the reaction of an acid with an insoluble reactant.
- Add excess carbonate/metal/ base to warm acid until no further acid.
- Filter mixture to remove unreacted solid.
- Heat filtrate in evaporating dish till saturated.
- Cool solution to obtain salt.
- Dry salts between sheets of filter paper.
Why is reaction of acid with insoluble reactant only suitable for soluble salts?
If this method were to be used to prepare an insoluble salt, insoluble salt produced will form a ‘protective layer’ over insoluble reactant, preventing any further reaction and hence a lower yield.
Why must an excess of insoluble reactant be added for RAIR?
Ensure all acid completely reacted, prevent any excess acid which will contaminate the aqueous salt formed. Excess reactant on the other hand can be removed easily though filtration.
Suggest why group I salts may not be prepared through RAIR with an excess of a group I base or carbonate.
They are all soluble in water, hence any excess reactant will not be able to be removed through filtration.
Suggest why group I salts may not be prepared through RAIR with excess of group I metals.
They are very reactive, hence react violently with acids, causing experiment to be too dangerous to perform.
Suggest why titration needs to be repeated a second time without using an indicator.
During first titration, salt sample produced has been contaminated by indicator added. Repeating without indicator will produce pure salt sample without contamination.
Why an alkali or carbonate must be used in titration, instead of a metal salt?
Only by product is water for alkali and carbonate. If metal salt used, by product will contaminate salt.
Describe the process of titration.
- Meade out fixed volume of acid using pipettes. Transfer this solution into comical flask.
- Add few drops of indicator.
- Add alkali/carbonate drop by drop until indicator changes color using burette.
- Note down volume of alkali/carbonate required for complete neutralization.
- Repeat titration without indicator. Stop burette when reading reached same level as earlier noted.
