ACIDS, BASES AND SALTS

 

Acids
Acids is defined as the one which produces hydrogen ions in water. For Example, Sulphuric Acid, Hydrochloric Acid etc.
They give sour taste.
Acids turn blue litmus to red. This is used as confirmation test for the presence of acid.
When acids react with metals, gases are evolved.                                                                             
Reactions with Acids
1. Reaction of Acid with Metal
Acid + Metal → Salt + Hydrogen gas
Mg + H2 SO4 → H2 + Mg SO4.                                                                                                                                                                                                         2. Reaction of Acid with Carbonates
Na2 CO3 (s) + 2 HCl (aq) → 2NaCl (aq) +H2O(l) + CO2(g)
 Classification of Acids
Acids are classified as Organic Acids and Mineral Acids. Acids which are derived from plants and animals, they are known as Organic Acids. For Example, Citric Acid from fruit. Mineral acids are inorganic acids such as Sulphuric Acid. They are dangerous to be used, so need more precautions.
Acids are also classified as Strong Acids or Weak Acids. Strong acid is an acid, that completely dissociates into ions in aqueous solutions. For Example, Sulphuric Acid, Hydrochloric Acid.
Weak acid is the one which does not dissociate completely into ions in aqueous solutions. For Example, Acetic Acid.
Acids can also be as Dilute Acid and Concentrated Acids. The one which has low concentration of acids in aqueous solution, they are known as Dilute Acids whereas the one which has high concentration of acids in aqueous solution, are known as Concentrated Acids.                                   
Bases
Bases are the one which produces hydroxide ions in aqueous solutions. Bases which are water soluble they are known as Alkalis.
They turn red litmus to blue.
They have a bitter taste.
They also produced carbon-dioxide when reacted with carbonates.
They also evolved hydrogen gas when bases react with metals.                                                  
Reactions of Bases
1. Reaction with Metals
Base reacts with metals and produce hydrogen gas.
2NaOH + Zn → Na2 → Na2ZnO2 + H2.                                                                                                     2. Reaction of Acid with Carbonates
  Na2 CO3 (s) + 2 HCl (aq) → 2NaCl (aq) + H2O(l) + CO                                                                                          2(g)                                                                   

Classification of Bases
Bases are classified as Strong Base and Weak Base. Strong base is the one which dissociates completely into its ions in aqueous solution. For Example, NaOH.
Weak base is the one which does not dissociate completely into its ions in aqueous solutions. For Example, Ammonium Hydroxide, NH4OH.                          
Similarity between Acids and Bases
Both acids and base react with water. They produce ions in water
Both acids and bases acts as electrolytes, so are good conductors of electricity.
Both of them changes the colour of the litmus paper.                                                                                   
Strength of Acid or Base Solutions                                  Strength of an acid or base can be determined using a pH scale. It is a scale to measure the hydrogen ion concentration in a solution. The p stands for ‘potenz’, it is a German word which means power.
If pH is equal to 7, means the solution is neutral.
If pH is greater then 7 means alkaline solution.
If pH is less then 7 means the solution is acidic.  
    
Salts
When acid and base neutralize, salts are formed. Strong acid and strong base combines to form neutral salt.
NaOH + HCl → NaCl + H2Oq.                                 1. Formation of Neutral Salt
Strong acid and weak base combine to form acidic salt. For Example, Hydrochloric Acid and ammonium hydroxide combine to form ammonium chloride. Other examples, sodium hydrogen carbonate, sodium hydrogen sulphate etc.
HCl + NH4OH → NH4Cl + H2O
Eq.2. Formation of Acidic Salt
Similarly, weak acid and strong base combine to form basic salt. For Example, Acetic Acid and sodium hydroxide combine to form sodium acetate. Other examples are calcium carbonate, potassium cyanide etc.
CH3COOH + NaOH → CH3COONa + H2O
Eq.3. Formation of Basic Salt
The most common salt is table salt or sodium chloride (NaCl).                                        
                                                   
Indicators
They are the substances that which indicate acidic or basic nature of the solution using colour change. For Example, litmus solution, methyl orange, phenolphthalein, methyl red etc. Acids convert blue litmus paper red in colour. Bases turn red litmus blue. Phenolphthalein remains colourless in presence of acids but turn pink in presence of bases.                                         
Indicator
Original Colour
Acid
Base
Red litmus
Red
No Change
Blue
Blue litmus
Blue
Red
No change
Turmeric
Yellow
No Change
Reddish brown
Red cabbage juice
Purple
Reddish
Greenish yellow
Phenolphthalein
Colourless
Colourless
Pink
Methyl Orange
Orange
Red
Yellow
Onion
n/a
No change
Smell vanishes
Vanilla
n/a
No change
Smell vanishes