Get premium membership and access revision papers with marking schemes, video lessons and live classes.

Processing. Please wait.

Types of salts and laboratory preparation of salts

Answer Text:
Salts
- Is a compound formed when cations derived from a base combine with anions derived from an acid.
- Salts are usually formed when an acid reacts with a base i.e. when the hydrogen ions in an acid re wholly or partially by a metal ion or ammonium (NH4+) radical.
Laboratory preparations of salts
- Salts are prepared in the laboratory using various depending on property of the salt especially solubility
Examples
(a). Preparations by direct synthesis
Equation:
Fe(s) + Cl2(g) 2FeCl3(s)
(b). Reactions of acids with metals, metal oxides,
metal hydroxides and metal carbonate
Equations:
#Zn(s) + H_2SO_4(aq) to ZnSO_4(aq) + H_2(g)#
#CuO(s) + H_2SO_4(aq) to CuSO_4(aq) + H_2O(l)#
#NaOH(aq) + HCl(aq) NaCl(aq) + H_2O(l)#
#PbCO_3(s) + 2NHO_3(aq) Pb(NO3)_2(aq) + CO_2(g) + H_2O(l)#
Note:
-Acid + metal method will not be suitable if:
- The metal is too reactive e.g. sodium or potassium.
-The salt formed is insoluble; as it will form an insoluble layer on the metal surface preventing further reaction.
- The metal is below hydrogen in the reactivity series.
(c). Double decomposition/ precipitation
- Mainly for preparations of insoluble salts
- Involves formation (precipitation) of insoluble salts by the reaction between two solutions of soluble salts.
Equations:
#Pb(NO3)_2(aq) + 2NaCl(aq) to PbCl_2(s) + 2NaNO_3(aq)#
#AgNO_3(aq) + HCl(aq) to AgCl(s) + HNO_3(aq)#
Types of salts:
- Are categorized into three main categories:
-Normal salts
-Acid salts
-Double salts
-Solubility of salts: - a summary
- All common salts of sodium, potassium and ammonium are soluble.
- All common nitrates are soluble.
- All chlorides are soluble except silver, mercury and lead chlorides.
- All sulphates are soluble except calcium, barium, lead and stomium sulphates.
- All carbonates are insoluble except sodium, potassium and ammonium carbonates.
- All hydroxides are insoluble except sodium, potassium ammonium and calcium hydroxides is sparingly soluble.
Note:
- Lead(II) chloride is soluble in hot water.
- Calcium hydroxide is sparingly soluble in water.