Physical Science

 Class 10

    Acids, Bases and Salts

 

•        Acids: 

− Acids are substances containing hydrogen and can donate a hydrogen ion to another substance.

                              − They have sour taste.

                              − They turn blue litmus paper red.

− They do not change the colour of red litmus paper. − E.g. -Hydrochloric acid (HCl)

       -Sulfuric acid (H₂SO₄)

     -Nitric acid (HNO₃)        

    -Acetic acid (CH₃COOH)

 

•        Bases:

− Bases are substances which accepts hydrogen ion.

− They have bitter taste.

− They feel soapy or slipper on the skin.

− They turn red litmus paper blue.

− They do not change the colour of blue litmus paper. − E.g. -Sodium hydroxide (NaOH)

       -Ammonia (NH₃)

       -Potassium hydroxide (KOH)       

 -Magnesium hydroxide (Mg(OH)₂) 

 

 

•        Salts:

− Salts are substances which is obtained by the reaction of an acid and a base.

− The general formula for a salt is, Acid + Base → Salt + Water

− E.g. -Sodium chloride (NaCl)

  -Potassium chloride (KCl)   -Calcium chloride (CaCl₂)

 

•        Indicators:

− An indicator is a substance that changes colour to indicate the presence or absence of acid or base in a solution.

− E.g. 

1.    Litmus paper -It is a natural indicator.

                 -It is extracted from a plant, lichen.

                -Blue litmus turns red in acidic medium.                 -Red litmus turns blue in basic medium.

 

2.    Turmeric -It is natural indicator.

 -Yellow coloured turmeric becomes reddish-brown in basic medium.

3.    Phenolphthalein -Chemical compound of formula C₂₀H₁₄O₄.

 -It turns colourless in acidic solution. -It turns pink in basic solution.

4.    Methyl orange -It is chemical compound.

-It turns from orange to red in acidic medium. -It turns from orange to yellow in base.

 

 

 

•        Chemical properties of acids and bases:

 

S.No	Properties	Acids	Bases
1.	Taste	Sour	Bitter
2.	Touch	Do not feel slippery	Feels slipper
3.	pH	pH < 7	pH > &
4.	Corrosion	Corrode metals	Do not corrode metals
5.	Reacts with metals	React with metals to produce a compound and hydrogen gas	Do not react with metals.
6.	Litmus	Blue to red	Red to blue

 

•        Reaction of Acids and Bases:

1. With metals o Acids react with metals, which results in the formation of hydrogen gas and salt.

i.e. Acid + Metal → Salt + Hydrogen gas

E.g.   H₂SO₄ + Zn → ZnSO₄ + H₂ o Bases react with metals to form salt and hydrogen gas.

i.e. Base + Metal → Salt + Hydrogen Gas

E.g.  2NaOH + Zn → Na₂ZnO₂ + H₂

 

 

2. With each other o Neutralisation reaction – the react ion between an acid and a base to form a salt and water is known as neutralisation reaction.

i.e. Acid + Base → Salt + Water

E.g.  HCl + NaOH → NaCl + H₂O

 

•        Chemicals from salts:

1. Sodium chloride (NaCl) 

-  It is the raw material for chemicals. - Chemicals used in daily life are made from sodium chloride.

-  Also known as ‘brine’.

2. Sodium hydroxide (NaOH)

-                  Formed when electricity is passed through aqueous solution of brine.

-                  This process is called ‘Chlor-alkali’ process. - 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂

3. Baking soda (NaHCO₃)

-  Chemical name is sodium hydrogencarbonate.

-  Commonly used in the kitchen.

-  Its formation is given as,

NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃

 

 

•        Strength of Acids and bases:

− pH scale- It is a scale used to measure the hydrogen ion concentration in a solution.

-  The pH of acidic solution is 0-7, Basic solution is 7-14, and of neutral solution is 7.

− Strength of acids and bases depends on the number of hydrogen ions and hydronium ions produced, respectively.

 

− pH of,

-  Human body- 7.0 to 7.8

-  Acid rain- 5.6

-  Salts of strong acid and strong base- 7

-  Salts of strong acid and weak base- less than 7

-  salts of strong base and weak acid- more than 7