شرح درس
Acids and Bases
CHEMISTRY - Secondary 1
In This part we will study
 The Arrhenius' theory in 1887:
 Arrhenius observed that the aqueous solutions of acids and bases conduct electricity.
 This observation proves that acids and bases are ionized in water.
Dissolving of hydrogen chloride in water
When hydrogen chloride gas dissolves in water, it is ionized into hydrogen ions (H+) and chloride ions (Cl- ).
HCl □(→┴"H2O(l)" ) H+(aq) + Cl-(aq)
Arrhenius acid: It is the substance that dissolves in water and ionized or dissociated giving one or more hydrogen ions (H+).
According to Arrhenius' theory we observe that
Arrhenius acid must contain a source of hydrogen ions (H+).
So;
Arrhenius acid works on increasing the concentration of (H+) ions in the aqueous solutions.
H2SO4 □(→┴Water ) H+(aq) + 〖HSO〗_4^-

Dissolving of sodium hydroxide in water
When sodium hydroxide dissolves in water, it is dissociated to sodium ions (Na+) and hydroxide ions (OH-).
NaOH □(→┴"H2O(l)" ) Na+(aq) + OH-(aq)

Arrhenius Base: It is the substance that dissolves in water and ionized or dissociated giving one or more hydroxide ions (OH- ).
According to Arrhenius' theory we observe that
Arrhenius base must contain a source of hydroxide ions (OH-).
So;
Arrhenius base works on increasing the concentration of (OH-) ions in the aqueous solutions.
KOH(s) □(→┴Water ) K+(aq) + OH-(aq)

Examples:
Classify the following substances into Arrhenius acid or Arrhenius base, giving reasons :
(1) HNO3(l)
(2) Mg(OH)2(s)
Solution

(1) HNO3(l) HNO3(l) □(→┴"H2O(l)" ) H+(aq) + 〖"NO" 〗_"3" ^"-" (aq)
- HNO3 is an Arrhenius acid, because it dissolves in water giving H+ ions.

(2) Mg(OH)2(s) Mg(OH)2(s) □(→┴"H2O(l)" ) Mg2+(aq) + 2〖"OH" 〗_((aq))^"-"
- Mg(OH)2 is an Arrhenius base, because it dissolves in water giving OH- ions.

Neutralization reaction: is the reaction between an acid and a base to produce salt and water.
Observations on (Defects of) Arrhenius' theory
Arrhenius' theory is deficient, as it cannot define all types of acids and bases, for example it cannot explain the fact that:
 Carbon dioxide CO2 doesn't contain a source of (H+) ions, but it dissolves in water giving an aqueous acidic solution.
 Ammonia NH3 doesn't contain a source of (OH-) ions, but it dissolves in water giving an aqueous basic solution.

Best wishes to you
Mr.Ahmed Elbasha

كيمياء الصف الاول الثانوي لغات - الفصل الدراسي الاول
شرح كيمياء لغات اولي ثانوي - مستر احمد الباشا
كيمياء لغات - الصف الاول الثانوي - كيمياء اولي ثانوي الترم الاول - كيمستري اولي ثانوي الترم الاول