C7.01 Rules for solubility
| substance | solubility | example | formula | exceptions |
| most sodium, potassium and ammonium salts | soluble | sodium chloride | NaCl | |
| all nitrates | soluble | lead nitrate | PbNO3 | none |
| most ethanoates | soluble | sodium ethanoate | CH3COONa | |
| most chlorides | soluble | copper chloride | CuCl2 | silver chloride AgCl, lead chloride PbCl2 |
| most sulfates | soluble | magnesium sulfate | MgSO4 | lead sulfate PbSO4, barium sulfate BaSO4, calcium sulfate CaSO4 |
| carbonates | insoluble | calcium carbonate | CaCO3 | sodium carbonate Na2CO3, potassium carbonate K2CO3, ammonium carbonate (NH4)2CO3 |
| hydroxides | insoluble | iron III hydroxide | Fe(OH)3 | sodium hydroxide NaOH,
potassium hydroxide KOH, ammonium hydroxide NH4OH |
learning activity - Use the table to
name and give formulae of 10 salts.
Use the table to give the formulae of 5 soluble compounds and 5 insoluble ones.
Use rules to name 5 different soluble compounds - give formulae as extension.
Use rules to name 5 different insoluble compounds - give formulae as extension.
C7.02 Choosing a method for salt preparation
Salts can be made by the following methods:
direct combination
not normally used in school labs
e.g. iron + sulphur ----> iron sulphide
adding a carbonate to an acid
carbonate + acid ---> salt + water + carbon dioxide
calcium carbonate + hydrochloric acid ---> callcium chloride + water + carbon
dioxide
normally used to make soluble salts from insoluble carbonate, the reaction is
complete (the acid is neutralised) when the effervescence (fizzing) finishes and
some undissolved solid remains, filter, crystallise, filter again, wash and dry
to obtain salt
adding a metal to an acid
metal + acid ---> salt + hydrogen
iron + sulfuric acid ---> iron II sulfate + hydrogen
normally used to make soluble salts, the reaction is complete (the acid is
neutralised) when the effervescence (fizzing) finishes and some undissolved
solid remains, filter and crystallise, filter again, wash and dry to obtain salt
adding an base to an acid
acid + base ---> salt + water
normally used to make soluble salts from an insoluble base (most oxides and
hydroxides),
nitric acid + copper oxide ---> copper nitrate + water
the reaction is complete (the acid is neutralised) when some undissolved solid
remains, filter and crystallise, filter again, wash and dry to obtain salt
If a solution of a soluble base (an alkali e.g. soluble hydroxide) is used
titration is carried out first to find out how alkali to add, crystallise,
filter, wash and dry to obtain salt
learning activity - complete and extend the table below:
| salt | solubility | method- choose from (acid-carbonate, acid-metal, acid-base) | what to mix |
| copper sulfate | soluble | acid-base | copper oxide, sulfuric acid |
| zinc nitrate | |||
| calcium chloride |
C7.03 Forming precipitates
precipitation
soluble salt1 + soluble salt2 ----> insoluble
salt + soluble salt3
sodium chloride + lead nitrate ----> lead chloride + sodium nitrate
used to make insoluble salts from two solutions of soluble salts
learning activity - choose suitable pairs of solutions to
make the following insoluble salts:
calcium carbonate, barium sulfate, silver chloride, zinc carbonate, and lead
chloride.
C7.04 Purification of insoluble salts
When made an insoluble salt made is filtered, washed with distilled water
and dried.
learning activity - draw a set of labelled diagrams to
show how a pure dry sample of the insoluble salt calcium sulfate can be made
from solutions of calcium nitrate and sodium sulfate.