chemistry salt preparations

making insoluble salts

precipitation reaction, using two soluble salts

making soluble salts

acid + insoluble base (metal oxide/metal hydroxide), base is in excess

or

acid + base with titration

compounds of sodium (Na⁺)

all soluble

compounds of potassium (K⁺)

all soluble

compounds of ammonium (NH₄⁺)

all soluble

all nitrates (NO₃⁻)

all soluble

all chlorides (Cl⁻)

all soluble except

lead (II) chloride (PbCl₂)

& silver chloride (AgCl)

all sulfates (SO₄²⁻)

all soluble except

barium sulfate (BaSO₄),

lead (II) sulfate (PbSO₄),

calcium sulfate (CaSO₄),

& silver sulfate (Ag₂SO₄)

all carbonates (CO₃²⁻)

all insoluble except

sodium carbonate (Na₂CO₃),

potassium carbonate (K₂CO₃),

& ammonium carbonate ((NH₄)₂CO₃),

all hydroxides (OH⁻)

all insoluble except

sodium hydroxide (NaOH),

potassium hydroxide (KOH),

ammonium hydroxide (NH₄OH),

& calcium hydroxide (Ca(OH)₂)

making soluble salts (except sodium, potassium, ammonium)

react a acid with excess of insoluble solid metal (base)

- acid + metal (only for metals from magnesium to iron)

- acid + metal oxide or hydroxide

- acid + carbonate

making soluble salts (for sodium, potassium, ammonium)

use titration method, react acid with solution of sodium/potassium hydroxide/carbonate or ammonia solution

[sodium, potassium, ammonium compounds are soluble in water -> will react with acid and will dissolve in water present]

how to prepare a soluble salt (not sodium, potassium, ammonium salts)

- made from reaction of acid with insoluble base

- insoluble base added in excess, ensure all acid reacts (if step is not completed, unreacted acid would become dangerously concentrated during evaporation & crystallisation)

- excess reactant removed by filtration (ensures only salt & water remain)

- heat solution with bunsen burner to evaporate water

- leave solution to cool and allow to crystallise

- filter off solid salt

- acid could also be reacted with a metal to produce salt (if metal is more reactive than hydrogen and is not too reactive so that a dangerous reaction doesn't take place)

how to prepare sodium, potassium, ammonium salts with titration

- made from titration of acid with alkali (soluble)

- use pipette to alkali into conical flask and add a few drops of indicator

- add acid into burette, not starting volume

- add acid slowly from burette into conical flask until indicator changes colour

- record final volume of acid in burette, calculate volume of acid added

- add same volume of acid into same volume of alkali without indicator

- leave to crystallise, leave crystals to dry

how to prepare an insoluble salt

- made using precipitation reaction

= uses 2 soluble salts (soluble salt 1 + soluble salt 2 -> insoluble salt + soluble salt 3)

- measuring fixed volume of 1 solution then adding second salt solution until it is in slight excess -> ensures maximum precipitate obtained

- precipitate recovered by filtration and washed with distilled (deionised) water and is left to dry

- starting material will usually be nitrate of silver/lead