Salts formation methods & types of aqueous solutions of salts
Salts formation methods
Salts can be practically prepared by Reaction of active metals with diluted acids , Reaction of metal oxides with acids , Reaction of metal hydroxides with acids and Reaction of metal carbonates or bicarbonates with some acids .
Reaction of active metals with diluted acids
Active metal + acid ( dil ) → Salt of acid + Hydrogen gas ↑
Example : Reaction of zinc with diluted sulphuric acid .
Zn ( s ) + H2SO4 ( aq ) → ZnSO4 ( aq ) + H2 (g) ↑
Reaction of metal oxides with acids
Metal oxide + Acid ( dil ) → Salt of acid + Water
This method is used if there is a difficulty in the direct reaction of metal with acid because the reaction is dangerous ( e.g. the reaction of sodium with hydrochloric acid is vigorous ) , The metal doesn’t react with the acid , because it is less reactive than hydrogen ( e.g. copper doesn’t react with hydrochloric acid ) .
Example : Reaction of copper oxide with sulphuric acid .
CuO( s ) + H2SO4 ( aq ) → CuSO4 ( aq ) + H2O (l) ↑
Reaction of metal hydroxides with acids
This method is suitable in the case of metal hydroxides , that are dissolving in the water and considered as alkalis , These types of reactions are known as Neutralization reactions .
Neutralization reactions can be used in analytical chemistry to calculate the concentration of an acid ( or an alkali ) using a known concentration of a base ( or an acid ) in the presence of a suitable indicator .
Neutralization point ( End point ) is the moment at which the amount of acid is equivalent to the amount of alkali .
Metal hydroxide ( alkali ) + Acid ( dil ) → Salt of acid + Water
NaOH ( aq ) + HCl ( aq ) → NaCl ( aq ) + H2O ( l )
Reaction of metal carbonates or bicarbonates with some acids
Metal carbonates ( or bicarbonates ) + Acid → Salt of acid + Water + Carbon dioxide gas ↑
Metal carbonates or bicarbonates are salts of carbonic acid which is an unstable acid , due to its low boiling point .
It is possible for any other acid ( that is more stable than it ) to remove it from from its salt solutions to form a new acid salt .
Example : Reaction of sodium carbonate with hydrochloric acid
Na2CO3 ( s ) + 2 HCl ( aq ) → 2NaCl ( aq ) + H2O ( l ) + CO2 ( g ) ↑
The reaction of metal carbonates or bicarbonates with some acids is called acidity test because this reaction is used to detect the presence of acids , as a strong effervescence occurs and CO2 gas evolves , which turns the clear limewater into turid .
Types of aqueous solutions of salts
The aqueous solution of sodium chloride is neutral because NaCl is produced from the reaction between a strong acid ( HCl ) and a strong base ( NaOH ) , So , the pH value is 7 .
The aqueous solution of sodium carbonate is basic because Na2CO3 is produced from the reaction between a strong base ( NaOH ) and a weak acid ( H2CO3 ) , So , its pH value > 7 .
The pH value of an aqueous solution of ammonium chloride is less than 7 because this solution is an acidic , where NH4Cl is produced from the reaction between a strong acid ( HCl ) and a weak base ( NH4OH ) .
The pH value of an aqueous solution of ammonium acetate equals 7 because this solution is a neutral , where CH3COONH4 is produced from the reaction between a weak acid ( CH3COOH ) and a weak base ( NH4OH ) .