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salt preparation procedures (preparation of insoluble salts…
salt preparation procedures
preparation of insoluble salts (PRECIPITATION)
reaction involving mixing 2 aqueous solutions to form an insoluble solid that separates out from reaction mixture. insoluble solid is precipitate
2 solutions selected. 1 reagent contributes cation Xn+ nitrate while another contributes sodium anion Ym-
eg, to prepare insoluble salt PbSO4, can mix 2 aqueous solutions (lead (ii) nitrate --> Pb2+ cation) and (sodium sulfate --> SO42- anion)
mix 2 solutions together. 1 reagent added in excess and would be left as unreacted reagent
when lead (ii) nitrate and sodium sulfate mixed, insoluble salt (PbSO4) and aqueous solution NaNO3 formed.
insoluble salt formed as precipitate, then be separated from aqueous solution by filtration (residue is lead(ii) sulfate precipitate (need to name residue collected)
salt then washed with distilled water, wiped dry with filter paper to remove contaminant chemicals that are on surface of crystals
preparation of soluble salts
reaction of acid with insoluble substance (solid-acid reaction)
acid added to insoluble solid reactant (include carbonate, base (hydroxides or oxides) and metal (added in excess)
acid + metal --> salt + hydrogen
acid + alkali --> salt + water
acid + carbon dioxide --> salt + water + carbon dioxide
note: first reaction should not be used with highly reactive metals (eg group 1 metals) and will not work with unreactive metals (gold, silver, copper)
fill beaker with dilute ___ acid
with constant stirring, add ___ oxide (insoluble solid, a little at a time, with stirring, to acid until solid is in excess or until no more effervescence observed ( for case of carbonate and metal only)
filter mixture, to remove excess unreacted insoluble solid. collect filtrate. filtrate is (name of salt solution)
heat filtrate gently until it is saturated
allow saturated solution to cool for crystals to form
filter mixture to collect crystals
wash soluble salt crystals with small amount of cold distilled water
dry crystals between pieces of filter paper
evaporation to dryness acceptable for salts that do not decompose on heating or without water of crystallisation
titration involving acid and soluble carbonate/ alkali
used to produce ammonium salt and grp 1 ions (both are soluble)
acid + alkali -> salt + water
acid + soluble carbonate --> salt + carbon dioxide + water
after end point of reaction, experiment repeated without indicator so final products contain only salt and water. salt can then be collected by crystallization and dried with filter paper
fill burette with dilute __ acid
pipette 25.0cm3 of aqueous (name of cation which are soluble eg group 1 or ammonium) hydroxide into conical flask
add few drops of appropriate ndicator (eg methyl orange indicator) to solution in conical flask
titrate
solution with dilute
acid until indicator just changes color
note volume of dilute nitric acid added
repeat experiment without indicator
add same volume of acid (froms tep 5) from burette. this gives solution of salt, without excess acid or alkali
heat solution to saturated
allow solution to coool for crystals to form
filter mixture to remove excess solution/water
wash crystals with small amount of cold distilled water
dry crystals by pressing between sheets of filter paper