Properties of Acids and Bases & Theories defining acids and bases
The acids and bases represent a large part of human life , Acids are used in many chemical industries like Fertilizers , Medicines , Plastic & Car batteries , Bases also have many uses in chemical industries like Soap , Detergents , Dyes & Medicines .
For example , The vinegar that is used in some food and cleaning processes is an acidic solution that was early discovered .
Natural and industrial products and the acids and bases entering in their composition or preparation
Acidic plants ( lemon – oranges – tomatoes ) contain Citric acid and Ascorbic acid , Dairy products ( milk – cheese – yoghurt ) contain Lactic acid , Soft drinks contain Carbonic acid and Phosphoric acid .
Soap contains Sodium hydroxide , Baking soda contains Sodium bicarbonate , Washing soda contains Hydrated sodium carbonate .
Properties of Acids
Na OH (aq ) + HNO3 ( l ) → NaNO3 (aq ) + H2 O ( l)
Acids react with active metals producing salt of acid and hydrogen gas H2 evolves .
Zn ( s ) + 2 HCL (aq ) → ZnCl2 (aq ) + H2 ( g ) ↑
Na2 CO3 ( s ) + H2 SO4 ( aq ) → Na2 SO4(aq ) + H2 O ( l ) + CO2 ( g ) ↑
Properties of Bases
Theories defining acids and bases
The external appearance of the acid and base leads to an experimental definition for each , The experimental definition is based on observation only and doesn’t describe or explain the unseen properties .
The more overall definitions of acid and base come from the studies and experiments that were placed in the form of theories , Acid-base theories are Arrhenius’s theory , Bronsted- Lowry’s theory and Lewis’s theory .
Arrhenius’s theory in 1887
Dissolving of hydrogen chloride in the water : When hydrogen chloride gas dissolves in the water , It is ionized into hydrogen ions ( H+ ) and chloride ions ( Cl−) , Dissolvig of acid in the water produces hydrogen ions .
Dissolving of sodium hydroxide in the water : When sodium hydroxide dissolves in the water , It is dissociated to sodium ions ( Na+ ) and hydroxide ions ( OH− ) , Dissolving of base in the water produces hydroxide ions .
Arrhenius base is the substance that dissolves in the water and ionized or dissociated giving one or more hydroxide ions ( OH− ) .
According to Arrhenius’s theory we observe that Arrhenius acid must contain a source of hydrogen ions ( H+ ) , Arrhenius base must contain a source of hydroxide ions ( OH− ) .
Explaining neutralization reaction according to Arrhenius’s theory
HCl ( aq ) + NaOH ( aq ) → NaCl ( aq ) + H2 O ( l )
The ionic equation of this reaction according to Arrhenius’s theory is :
H+(aq) + Cl−(aq) + Na+ (aq) + OH−( aq ) → Na+ (aq) + Cl−(aq) + H2 O ( l )
Na+ (aq) and Cl−(aq) ions are present in both sides of the equation without changing , So , they can be neglected ( cancelled ) from the both sides of the chemical equation , So , the neutralization reaction can be represented by the following equation :
H+(aq) + OH−( aq ) → H2 O ( l )
Observations on ( Deffects of ) Arrhenius’s theory
Ammonia NH3 doesn’t contain a source of ( OH− ) ions , but it dissolves in water giving an aqueous basic solution .
These observations do not agree with Arrhenius’s theory .
The Bronsted- Lowry’s theory in 1923
The Danish Scientist Bronsted and the British one Lowry proposed a new acid-base theory .
Bronsted-Lowry acid is the substance that give up the proton ( H+ ) , Proton donor .
Bronsted-Lowry base is the substance that accepts the proton ( H+ ) , Proton acceptor .
Bronsted-Lowry theory describes the behavior of ammonia as a base .
H2 O ( l ) + NH3 ( g ) → NH+4 (aq) + OH– (aq)
When ammonia gas dissolves in the water , H2 O acts as an acid because it gives up a proton ( H+ ) to ammonia molecule ( NH3 ) .
As a result of this transfer , OH– formed and it is called Conjugate base , Conjugate base is the substance which is formed when the acid loses a proton ( H+ ) .
, NH3 acts as a base because it accepts the proton ( H+ ) from the water molecule .
As a result of this transfer , NH+4 formed and it is called Conjugate acid , Conjugate acid is the substance which is formed when the base accepts a proton ( H+ ) .
Lewis’s theory in 1923
Lewis’s proposed an acid-base theory which depends on sharing of a lone pair of electrons between acid and base , Lewis acid is the substance that accepts an electron pair or more , Lewis base is the substance that donates an electron pair or more .
Ammonia is considered as a base , although it does not contain hydroxide group in its structure , Because according to Bronsted – Lowry’s theory , Ammonia accepts a proton from another substance ( as water ) during the reaction and according to Lewis’s theory it donates a lone pair of electrons to another substance ( as water ) during the reaction .