CBSC Science

  • Importance of pH in everyday life :- --------------------------------------- I) Are plants and animals pH sensitive ?   -> Our body works within the pH range of 7.0 to 7.8 .  -> Organisms survive in this narrow pH range change.  -> When pH of rain water is less than 5.6 then it is called acid rain . It lowers the pH of river water when mix with it and the survival of aquatic life becomes difficult. II) pH of Soil :- pH of Soil   -> plants required a specific pH for their healthy growth.  -> In most plants, the optimum pH range is from 5.5 to 7.0 , but some plants will grow in more acid soil or may require a more alkaline level.   III) pH in our digestive system :- pH of digestive system   -> Our stomach produces hydrochloric acid which helps in the digestion of food without harming the stomach.   -> During indigestion stomach produces too much acid which causes pain and irritation . To get ride from thi...

 I) What happens to an Acid  in a Water Solution ? ->  The hydrogen ion produced in the presence of water in HCl. - >The separation of H+ ion from HCl molecules cannot occur in the absence of water.   HCl + H2O --------> H3O+  + Cl- - >Hydrogen ions cannot exist alone but exist after combines water molecules hence H+ (aq) or hydronium ion (H3O+) .   H+ + H2O --------> H3O+ II) What happens to an Base in a Water Solution ? - >Bases generate hydroxide (OH-) ions in water.  Bases which soluble in water are called alkalis .   Examples:-   a) NaOH(s) + H2O(l) --------> Na+(aq) + OH-(aq)  b) KOH(s) + H2O (l) ----------> K+ (aq) + OH- (aq)  c)  Mg(OH)2 (s) + H2O (l) ----------> Mg2+(aq) +2OH- (aq) III) Process of mixing of Acid or a Base with Water. - >The process of dissolving an acid or a base in water is a exothermic process .  - >We must take care when doing this process. Like mixing of c...

  I) Acids and Bases reacts with each other. - > When Acids reacts with Bases to form Salt and water as product. This reaction is also called as neutralisation reaction . Acid + Base ---------> Salt + Water  Example:- i) NaOH (aq) + HCl (aq) ---------> NaCl (aq) + H2O(l) ii) MgOH (aq) + HCl (aq) -------> Mg(OH)2 (aq) + H2O (l) iii) LiOH (aq) + HCl (aq) ---------> LiCl (aq) + H2O (l) iv) Ca(OH)2 (aq) + H2SO4 (aq) ---------> CaSO4 (aq) + H2O (l) II) Metallic Oxides reacts with Acids:- - > When Metallic Oxides reacts with Acids it gives Salt and Water as products. Metallic Oxide + Acid ------> Salt + Water Example :-  i)  CuO (s) + HCl (aq) -------> CuCl2 (aq) + H2O (aq) black colour                     blue-green colour ->We notice that tht the colour of the solution becomes blue-green due to the formation of copper(II) chloride in the reaction . ii) CuO (s) + H2SO4 (aq) -------> CuSO4 ...

                             • When Acids reacts with Metal.  ->  Acid + Metal ---------> Salt + Hydrogen gas. -> When Acids react with Metals it gives salt and liberate hydrogen gas. Example:- i) 2HCl (l)+ 2Na(s) ---------> 2NaCl(s)+ H2(g) ii) H2SO4 (l) + Mg (s) ----------> MgSO4(s) + H2 (g)  iii) 2CH3COOH (l) + 2Na(s) -------> 2CH3COONa (s) + H2 (g) • When Bases reacts with Metals: -> When bases reacts with metals it gives salt and Hydrogen gas . Base + Metal ---------> Salt + Hydrogen gas Example:-  I) 2NaOH (aq) + Zn (s) ----------> Na2ZnO2 (s) + H2 (s) II) NaOH (aq) + Al (s)  ----------> NaAlO2 + H2 (s) • Metal carbonate and metal hydrogen carbonate reacts with acids. -> When Metal carbonate/ Metal hydrogen carbonate reacts with acids to give Salt, Water and  releases Carbon dioxide gas. Metal carbonate/Metal hydrogen carbonate + Acid ------> ...