Salts Flashcards
Define salt
A salt is formed when hydrogen ions of an acid is partially or completely replaced by a metal ion or ammonium ion
Define water of crystallisation
Loosely associated water molecules with salts
Which method should be used to produce insoluble salt
Precipitation
Which method should be used to produce salts with less reactive ions
Reaction of acids with excess insoluble carbonates, bases or metals
Which method should be used to produce salts of group 1 metals or ammonium salts
Titration
Describe precipitation reaction
Mix two aqueous solutions in a beaker. Stir well and a (colour) precipitate will be formed. Filter mixture to obtain __ as residue. Wash residue with deionised water and dry residue between sheets of filter paper
Why is insoluble reactant unsuitable for preparing insoluble salt(e.g. calcium carbonate + sulfuric acid)
Calcium carbonate reacts with sulfuric acid to form insoluble salt, calcium sulfate which will coat onto surface of calcium carbonate, preventing further reaction between calcium carbonate and sulfuric acid.
Describe preparation of zinc sulfate using zinc metal and dilute sulfuric acid
Heat acid in beaker. Add excess insoluble zinc to acid and stir mixture well. Filter mixture to remove excess zinc as residue and collect zinc sulfate solution as filtrate. (+ crystallisation of solution)
Why is dilute acid heated during preparation of soluble salt
To speed up the reaction
Why is excess solid reactant is used in preparation of soluble salt
To ensure that all the acid has completely reacted with insoluble base/carbonate/reactive metal. This will ensure resulting salt solution is free from acid contamination
Why is stirring necessary in preparation of soluble salt
To mix reactants well for complete reaction
Why must hot solution be cooled to form crystals during crystallisation
As temperature decreases, solubility of salt decreases, hence salt will crystallise from the solution
Why cant evap to dryness be used to obtain the crystals after preparation of soluble salt
Upon heating, hydrated salt may lose water of crystallisation and become anhydrous salt. Some salts may also decompose
Why should sodium sulfate not be prepared the same way as zinc sulfate
Reaction between group 1 metals and acids is highly explosive and not experimentally feasible to carry out safely
Describe titration
Pipette known value of alkali into conical flask and add a few drops of indicator. Add acid from burette to alkali until end-point where indicator changes color. Record volume of acid needed to neutralise alkali and repeat titration until consistent results are obtained. Repeat expt without adding indicator by adding recorded vol of acid into acid containing known volume of acid(+ crystallisation)
