Chemistry salt preparation Flashcards
Salt reactions
1) Acid + metal carbonate ➡️ salt + water + carbon dioxide
2) acid + metal hydrogen carbonate ➡️ salt + water + carbon dioxide
3) acid + metal hydroxide ➡️ salt + water
4) acid + metal oxide ➡️ salt + water
5) acid + metal ➡️ salt + hydrogen
Salt preparation 1
Soluble acid + soluble base ➡️ soluble salt + water
Purification - evaporation
Since a salt solution is produced, the solid salt needs to be isolated.
This is done by evaporation, to remove MOST of the water.
The crystalline salt can be dried on paper or left in a warm place/oven.
Salt preparation 2
Soluble acid + insoluble base ➡️ soluble salt + water (+ CO2)
Procedure - neutralisation
Add excess insoluble base/carbonate so that all acid fully reacts
Forms a salt solution (dissolved in water)
Salt preparation 2 - part 2
Purification- filtration THEN evaporation
Filtering the final solution removes any unreacted solid base.
Evaporating removes MOST of the water, as in the first method.
Salt preparation 3
Soluble acid + soluble base ➡️ insoluble salt + soluble salt
Procedure - precipitation
When two soluble ionic salts are combined, they can form an insoluble salt; a precipitate
Salt preparation 3 - part 2
Soluble acid + soluble base ➡️ insoluble salt + soluble salt
Purification - filtration
Filtering the mixture separates the insoluble salt, as the precipitate.
Salt preparation 3 - part 3
Soluble acid + soluble base ➡️ insoluble salt + soluble salt
Purification- washing THEN drying
Washing the precipitate to remove soluble impurities.
Oven drying to obtain dry salt.
Salt preparation 3 - part 4 example
Soluble acid + soluble base ➡️ insoluble salt + soluble salt
Write the balanced equation to show the formation of solid lead iodide from two solutions of lead nitrate and potassium iodide.
Pb(NO3)2(aq) + 2KI(aq) ➡️ Pbl2(s) + 2KNO3(aq)
Convert this into an ionic equation - remove any spectator ions
Pb2+(aq) +2l-(aq) ➡️ Pbl2(s)
Water of crystallisation
In both examples, a crystalline salt is produced which is hydrated or chemically combined with water. This is called water of crystallisation, e.g CuSO4.5H2O
If the salt is heated to complete dryness, it will be anhydrous with no water, e.g CuSO4
Define a hydrated substance
As a substance that is chemically combined with water and an anhydrous substance as a substance containing no water
Solubility rules - nitrate
All nitrates are soluble
Solubility rules - chloride
All chlorides are soluble except AgCl, PbCl2
Solubility rules - sulfates
All sulfates are soluble except CaSO4, PbSO4, BaSO4
Solubility rules hydroxides
All hydroxides are insoluble except those in group 1 and those of group 2 are slightly soluble
Solubility rules - carbonates
All carbonates are insoluble except those of group 1 and (NH4)2CO3
