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What is Photosynthesis ?

By Sachin Joshi
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Acid-base in water / Dilution / pH scale( universal indicator )

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By Sachin Joshi



 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 concentrated nitric acid or sulphuric acid with water. During this process the acid must added slowly to water with constant stirring.  
If water is added to concentrated acid, the heat generated cause the mixture to splesh out and cause burn. The glass container may also break due to excessive heating.  The warning sign ( shown below) on the can of concentrated Acids and on concentrated Bases are labelled.


- > Mixing an acid or base with water results in the decrease in the concentration of ions (H3O+/OH-) per unit volume and the process is called dilution and the acid or base is said to be diluted.

IV) How strong are  acid or base solution ?

- > Acid - Base indicators are used to distinguish between an acid or base(like Litmus paper, Methylorange, Phenolphthalein etc).
- > We can quantify and measure the strength of acid or base by measuring the ions present in a solution using universal indicator.

•What is universal indicator ?
-> Universal indicator is the mixture of several indicators which shows different colour at different concentrations of hydrogen ions in a solution.

•What is pH scale ?
- > A scale for measuring hydrogen ion concentration in a solution is called as pH scale. Where p stands for 'potenz' in German, meaning power.
- > On pH scale we measure pH generally from 0 ( very acidic) to 14 ( very alkaline). 
- >It is a simply as number on pH scale which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration , lower is the pH value.
- > Reading 7 on pH scale indicates neutral Solution.
- > Value less then 7 on pH scale represents an acidic solution and increase in H+ ion concentration.
-  >Reading more then 7 to 14 on pH scale represents an basic solution which also represents increase in OH- ion concentration in the solution ( alkali)

•Strong acids:-
       - > The acids that give rise more H+ ions are said to be strong acids.
Example:- Hydrochloric acid (HCl), Nitric acid (HNO3), Sulphuric acid (H2SO4) etc 
•Weak acid:-
      - >  The acids that give rise to less H+ ions are said to be weak acids.
Example:- Formic acid (HCOOH), Acetic acid (CH3COOH), Benzoic acid ( C6H5COOH) etc.

•Strong base:-
       - >  The bases that give rise to more OH- ions are said to be strong Base.
Example:- Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Calcium hydroxide(CaOH) etc.
 •Weak base:- 
       - >  The bases that give rise to less OH- ions are said to be weak Base.
Example:- Ammonia (NH3), Trimethylamine (N(CH3)3), Pyridine (C5H5N) etc.
 

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