An acid is a substance that dissolves in water to form H+/H3O+ as the only positive ion/cation.

This is called the Arrhenius definition of an acid.

From this definition, an acid dissociate/ionize in water releasing H+ thus:

HCl(aq)  ->  H⁺ (aq)   +    Cl^- (aq)

HNO₃ (aq)  -> H⁺(aq)   +    NO₃ ^- (aq)

CH₃ COOH(aq)  ->    H⁺ (aq)  +    CH₃ COO^- (aq)

H₂ SO₄ (aq)  ->  2H⁺ (aq)  +    SO₄ ^2- (aq)

H₂ CO₃ (aq)  ->  2H⁺ (aq)  +    CO₃ ^2- (aq)

H₃ PO₄ (aq)  ->  3H⁺ (aq)  +    PO₄ ^3- (aq)

A base is a substance which dissolves in water to form OH- as the only negatively charged ion/anion..

This is called Arrhenius definition of a base.

 From this definition, a base dissociate/ionize in water releasing OH- thus:

KOH(aq)   ->   K+(aq)   +   OH-(aq)

NaOH(aq)   ->   Na+(aq)   +   OH-(aq)

NH4OH(aq)   ->   NH4+(aq)   +   OH-(aq)

Ca(OH)2(aq)   ->   Ca2+(aq)   +   2OH-(aq)

Mg(OH)2(aq)   ->   Mg2+(aq)   +   2OH-(aq)

Fe(OH)2(s)         ->   Fe2+(aq)   +   2OH-(aq)

Al(OH)3(s)   ->   Al3+(aq)   +   3OH-(aq)

Fe(OH)3(s)   ->   Fe3+(aq)   +   3OH-(aq)

An acid is a proton donor.

A base is a proton acceptor.

This is called Bronsted-Lowry definition of acids and bases.

From this definition, an acid donates H+.

H+ has no electrons and neutrons .It contains only a proton.

Examples

1. From the equation:

 HCl(aq)   +  H2O(l)   ===    H3O+(aq) +   Cl- (aq)

(a)(i)For the forward reaction from left to right, H2O  gains a proton to form H3O+  and thus H2O is a proton acceptor .It is a Bronsted-Lowry base 

(ii) For the backward reaction from right to left, H3O+   donates a proton to    form H2O and thus H3O+  is an ‘opposite’ proton donor.

It is a Bronsted-Lowry conjugate acid

For the forward reaction from left to right, HCl  donates a proton to form Cl-  and thus HCl is a proton donor .

It is a Bronsted-Lowry acid 

(ii) For the backward reaction from right to left, Cl-   gains a proton to form HCl and thus Cl-  is an ‘opposite’ proton acceptor.

 It is a Bronsted-Lowry conjugate base.

Every base /acid from Bronsted-Lowry definition thus must have a conjugate product/reactant

From the equation:

HCl(aq)   +    NH3(aq)  ===    NH4+(aq)   +   Cl- (aq)

For the forward reaction from left to right, NH3  gains a proton to form NH4+ and thus NH3 is a proton acceptor .It is a Bronsted-Lowry base 

(ii) For the backward reaction from right to left, NH4+   donates a proton to form NH3 and thus NH4+  is an ‘opposite’ proton donor.

It is a Bronsted-Lowry conjugate acid

(b)(i)For the forward reaction from left to right, HCl  donates a proton to form Cl-  and thus HCl is a proton donor .It is a Bronsted-Lowry acid 

(ii) For the backward reaction from right to left, Cl-   gains a proton to form HCl and thus Cl-  is an ‘opposite’ proton acceptor.

It is a Bronsted-Lowry conjugate base.

Hydrogen chloride gas dissolves in water to form hydrochloric acid. Hydrochloric acid dissociates/ionizes in water to free  H+(aq)/H3O+(aq) ions.

The free H3O+(aq) / H+(aq)  ions are responsible for:

   (i)turning blue litmus paper/solution red.

  (ii)show pH value 1/2/3/4/5/6

  (iii)are good electrolytes/conductors of electricity/undergo electrolysis.

  (iv)react with metals to produce /evolve hydrogen gas and a salt. i.e.

  Ionically:

-For a monovalent metal: 2M(s)  +2H+(aq)-> 2M+(aq) + H2(g)

-For a divalent metal:        M(s) +2H+(aq)-> M2+(aq)  + H2(g)

-For a trivalent metal:        2M(s)+6H+(aq)->2M3+(aq) +3H2(g)

Examples:

-For a monovalent metal: 2Na(s) + 2H+(aq) ->2Na+(aq)+H2(g)

-For a divalent metal:   Ca(s)+2H+(aq)->Ca2+(aq)+H2(g)

-For a trivalent metal:   2Al(s) +6H+(aq)->2Al3+(aq) +3H2(g)

   (v)react with metal carbonates and hydrogen carbonates  to produce /evolve carbon(IV)oxide gas ,water and a salt. i.e.

  Ionically:

  -For a monovalent metal:

 M2CO3(s) + 2H+(aq) -> 2M+(aq) + H2O (l) + CO2(g)

MHCO3(s) + H+(aq)   -> M+(aq)   + H2O (l) + CO2(g)

  -For a divalent metal:

 MCO3(s) + 2H+(aq)  ->  M2+(aq)  + H2O (l) + CO2(g)

M(HCO3) 2(aq) + 2H+(aq)  -> M2+(aq)+2H2O(l) + 2CO2(g)

Examples:

  -For a monovalent metal:

 K2O(s)   +   2H+(aq)    ->   2K+(aq)    +  H2O (l)

 NH4OH(aq)   +    H+(aq)    ->  NH4+(aq)    +  H2O (l)

  -For a divalent metal:

 ZnO (s)   +  2H+(aq)    ->    Zn2+(aq)    +   H2O (l)

 Pb(OH) 2(s)    + 2H+(aq)    ->   Pb2+(aq)   +   2H2O(l)

(b)Hydrogen chloride gas dissolves in methylbenzene /benzene but does not dissociate /ionize into free ions.

 It exists in molecular state showing none of the above properties.

(c)Ammonia gas dissolves in water to form aqueous ammonia which dissociate/ionize to free NH4+ (aq) and OH-(aq) ions.

This dissociation/ionization makes aqueous ammonia to:

  (i)turn litmus paper/solution blue.

  (ii)have pH 8/9/10/11

  (iii)be a good electrical conductor

  (iv)react with acids to form ammonium salt and water only.

  NH4OH(aq)  +   HCl(aq)  ->   NH4Cl(aq)   +  H2O(l)

 (d)Ammonia gas dissolves in methylbenzene/benzene /kerosene but does not dissociate into free ions therefore existing as molecules.

6. Solvents are either polar or non-polar. A polar solvent is one which dissolves ionic compounds and other polar solvents. Water is polar solvent that dissolves ionic and polar substance by surrounding the free ions as below:

   Water is Polar. It is made up of:

   (i)Oxygen atoms which is partially (O ð-) negative

   (ii)Two Hydrogen  atoms which are partially (H ð+ ) positive

   A non polar solvent is one which dissolved non-polar substances and covalent compounds.

    If a polar ionic compound is dissolved in non-polar solvent ,it does not ionize/dissociate into free ions

   Some acids and bases are strong while others are weak.

   (a)A strong acid/base is one which is fully/wholly/completely dissociated / ionized into many free H+ /OH- ions i.e. 

   1. Strong acids exists more as free H+ ions than molecules. e.g.

     HCl(aq)  H+(aq)         +           Cl- (aq)   (molecules)                          (cation)              (anion)

     HNO3(aq)         H+(aq)      +          NO3- (aq)    (molecules)                         (cation)                           (anion)

      H2SO4(aq)  2H+(aq)      +          SO42- (aq)   (molecules)                          (cation)             (anion)

      KOH(aq)  K+(aq)      +          OH- (aq)   (molecules)                          (cation)             (anion) 

     NaOH(aq)  Na+(aq)      +          OH-(aq)   (molecules)                          (cation)             (anion)

   Strong bases/alkalis exists more as free OH- ions than molecules.

   A weak base/acid is one which is partially /partly dissociated /ionized in water into free OH- (aq) and H+(aq) ions.

   I.Weak acids exists more as molecules than as free H+ ions. e.g.

   CH3COOH(aq)  H+(aq)      +          CH3COO- (aq)

    (molecules)                        (cation)               (anion)

   H3PO4(aq)  3H+(aq)      +          PO43-(aq) (molecules)                        (cation)               (anion)

    H2CO3(aq)  2H+(aq)      +          CO32-(aq) (molecules)                        (cation)               (anion)

   1. Weak bases/alkalis exists more as molecules than free OH- ions. e.g.

   NH4OH(aq)           NH4+(aq)      +          OH- (aq) (molecules)                      (cation)                          (anion) 

   Ca(OH)2(aq)            Ca2+(aq)      +          2OH-(aq)     (molecules)                      (cation)               (anion)

   Mg(OH)2(aq)  Mg2+(aq)      +          2OH-(aq)      (molecules)                      (cation)               (anion)

1. Name some ampoteric oxides and hydroxides